Mader's Understanding Human Anatomy & Physiology 9th Edition PDF
Mader's Understanding Human Anatomy & Physiology 9th Edition PDF
Mader's Understanding Human Anatomy & Physiology 9th Edition PDF
Mader’s Understanding
Human Anatomy & Physiology
Published by McGraw-Hill Education, 2 Penn Plaza, New York, NY 10121. Copyright © 2017 by
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ISBN 978-1-259-29643-7
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5 The Integumentary
5.3 Functions of the Skin
5.4 Disorders of the Skin
92
93
System 86
I.C.E.—In Case of Emergency: Burns 96
5.1 Structure of the Skin 87 5.5 Effects of Aging 97
Medical Focus: Decubitus Ulcers 89 5.6 Homeostasis 97
5.2 Accessory Structures of the Skin 89 Medical Focus: Body Art: Buyer Beware! 98
iii
8 The Nervous
Medical Focus: Eye Diseases and Disorders 206
Focus on Forensics: Retinal Hemorrhage in Shaken Baby
System 162 Syndrome 208
8.1 Nervous System 163
9.4 Sense of Hearing 208
Visual Focus: Synapse Structure
9.5 Sense of Equilibrium 210
and Function 169
Medical Focus: Hearing Damage and Deafness 212
Medical Focus: Research on Alzheimer Disease: Causes,
Treatments, Prevention, and Hope for a Cure 170 9.6 Effects of Aging 213
8.2 Central Nervous System 171
What’s New: Epidural Stimulation in Spinal Cord Injuries: Cause
for Hope: In Memoriam: Christopher Reeve, 1952–2004 177 10 The Endocrine
What’s New: Brain in a Petri Dish: A Human Model for System 217
Alzheimer Research 178 10.1 Endocrine Glands 218
I.C.E.—In Case of Emergency: Traumatic Brain Injury 179 10.2 Hypothalamus and Pituitary
8.3 Peripheral Nervous System 180 Gland 222
Visual Focus: Autonomic System Structure and Function 185 Visual Focus: The Hypothalamus and the Pituitary 223
8.4 Effects of Aging 186 10.3 Thyroid and Parathyroid Glands 225
8.5 Homeostasis 187 10.4 Adrenal Glands 227
Medical Focus: Parkinson’s Disease 189 10.5 Pancreas 229
I.C.E.—In Case of Emergency: Insulin Shock and Diabetic
Ketoacidosis 232
9 The Sensory 10.6 Additional Endocrine Glands 232
System 193 What’s New: Options for Type I Diabetics: The Artificial Pancreas
9.1 General Senses 194 System, Beta Cell Transplants, and the BioHub 233
9.2 Senses of Taste and Medical Focus: Side Effects of Anabolic Steroids 234
Smell 196 10.7 The Importance of Chemical Signals 236
9.3 Sense of Vision 198 10.8 Effects of Aging 237
What’s New: Detecting Alzheimer Disease with Eye Exams 201 10.9 Homeostasis 237
Medical Focus: Corrective Lenses 205
iv Contents
11 Blood 242
13.4 Creating an Immune Response 305
Medical Focus: AIDS Epidemic 307
11.1 The Composition and Functions
of Blood 243 Medical Focus: Immunization: The Great
Protector 309
11.2 Components of Blood 244
Medical Focus: Influenza: A Constant Threat of
Visual Focus: Hematopoiesis 246 Pandemic 311
Medical Focus: Abnormal Red and White Blood Cell What's New: Parasite Prescription for Autoimmune
Counts 249 Disease 313
11.3 Platelets and Hemostasis 250 13.5 Effects of Aging 313
I.C.E.—In Case of Emergency: Hemorrhage 252 13.6 Homeostasis 315
11.4 Blood Typing and Transfusions 252
11.5 Effects of Aging 254
What’s New: Improvements in Transfusion Technology 255 14 The Respiratory
Focus on Forensics: Blood at the Crime Scene 256 System 318
14.1 The Respiratory System 319
I.C.E.—In Case of Emergency:
12 The Cardiovascular Lung Collapse 323
System 259 14.2 Mechanism of Breathing 325
12.1 Anatomy of the Heart 260 14.3 Gas Exchange and Transport 328
12.2 Physiology of the Heart 264 14.4 Respiration and Health 330
Medical Focus: Arteriosclerosis, Atherosclerosis, Medical Focus: The Most-Often-Asked Questions
and Coronary Artery Disease 267 About Tobacco and Health 333
Medical Focus: The Electrocardiogram 269 What's New: Bronchial Thermoplasty:
12.3 Anatomy of Blood Vessels 271 A Surgical Treatment for Asthma 336
12.4 Physiology of Circulation 274 14.5 Effects of Aging 336
I.C.E.—In Case of Emergency: Cardiopulmonary Resuscitation 14.6 Homeostasis 337
and Automated External Defibrillation 278
12.5 Circulatory Routes 278
Medical Focus: Preventing Cardiovascular Disease 285 15 The Digestive
12.6 Effects of Aging 286 System 342
What’s New: Novel Stent for the Severest Strokes 287 15.1 Anatomy of the Digestive
System 343
12.7 Homeostasis 287
Focus on Forensics: The Stories That Teeth
Can Tell 345
15.2 Accessory Organs of Digestion 353
13 The Lymphatic
Medical Focus: Disorders of the Digestive Tract 356
System and Body
Defenses 293 15.3 Chemical Digestion 358
13.1 Lymphatic System 294 15.4 Effects of Aging 360
13.2 Organs, Tissues, and Cells 15.5 Homeostasis 361
of the Immune System 294 15.6 Nutrition 361
Medical Focus: The Lymphatic System and Illness 297 Medical Focus: Tips for Effectively Using
13.3 Nonspecific and Specific Defenses 298 Nutrition Labels 364
Visual Focus: Steps of the Inflammatory Reaction 299 Medical Focus: Bariatric Surgery for Obesity 367
Contents v
17
The Reproductive 18
Human Development
System 392 and Birth 425
17.1 Human Life Cycle 393 18.1 Fertilization 426
17.2 Male Reproductive 18.2 Development 427
System 395
Medical Focus: Therapeutic
17.3 Female Reproductive System 401 Cloning 430
Visual Focus: Anatomy of Ovary and Follicle 402 18.3 Birth 437
Medical Focus: Ovarian Cancer 405 Medical Focus: Premature Babies 439
17.4 Control of Reproduction and Sexually Transmitted Medical Focus: Preventing Birth Defects 440
Infections 410
Medical Focus: Breast and Testicular
Self-Exams for Cancer 413 19 Human
Medical Focus: Endocrine-Disrupting Genetics 445
Contaminants 414
19.1 Chromosomal
Medical Focus: Preventing Transmission Inheritance 446
of STIs 418
19.2 Genetic Inheritance 450
17.5 Effects of Aging 419
19.3 DNA Technology 454
17.6 Homeostasis 419
Medical Focus: Preimplantation Genetic Studies 455
Focus on Forensics: Rape 421
What's New: A Profound Dilemma: Bioengineered Babies 457
Focus on Forensics: The Innocence Project 458
Appendix A A-1
Photo Credits C-1
Glossary/Index GI-1
vi Contents
Indiana) and a master’s degree in physiology from the Ohio State University, Susannah
Nelson Longenbaker began her teaching career at Columbus State Community College
in Columbus, Ohio. She continues to teach anatomy and physiology courses there, as
she has for over 30 years. During that time, she earned the college’s Distinguished
Teaching Award and Ohio Magazine’s Excellence in Education award. She founded and
serves as co-coordinator for Columbus State Community College Fantastic Fridays and
middle school and high school students to the fun and excitement of laboratory science.
In 2015, she was awarded the Columbus City Schools Community Excellence Award in
In 2006, Sue was offered a unique opportunity by Dr. Sylvia Mader: to become the
primary author for Understanding Human Anatomy and Physiology. Dr. Mader began
her long career as a college biology professor, then left the classroom to become one of
the most prolific authors of biology and human biology textbooks in the country. Her
works are well known for their direct writing style and carefully crafted pedagogy.
Dr. Mader’s many titles have been published and enjoyed by students worldwide for
almost 40 years.
Sue is honored to continue Dr. Mader’s legacy to education, as the writer for this
ninth edition of the textbook. She looks forward to and appreciates suggestions or
comments from instructors and students alike. Feel free to contact her at the following
address:
Sue Longenbaker
Department of Biological and Physical Sciences
Columbus State Community College
Columbus, Ohio 43215 (614) 287-2430
slongenb@cscc.edu
vii
viii
Reviewers
Melody Bell Barry Markillie Rebecca Roush
Vernon College Cape Fear Community College Sandhills Community College
Rolfe Bryant Craig Mauk Deborah Sanderson
Phillips Community College–Stuttgart KCTCS Gateway Community & Technical Piedmont Virginia Community College
Kim Zahn (Demnicki) College Hope Sasway
Thomas Nelson Community College Payman Nasr Suffolk CCC–BRENTWOOD
Cindy Hansen Kent State University–Ashtabula Jackie Spencer
Community College of Rhode Island– Jennifer Presley Thomas Nelson Community College
Warwick Ohio Valley University
Jaime Malcore Tjossem Susan Rainone
Rochester Community & Technical Community College of Rhode Island–
College Warwick
Preface ix
Learning Outcomes
at the beginning of every chapter will Learning Outcomes After you have studied this chapter, you should be able to:
help students understand what they 6.1 Skeleton: Overview 10. Name the bones of the vertebral possible steps for
column and the thoracic cage. Be damage prevention.
should know after studying the chapter. 1. Name at least five functions of the
skeleton.
able to label diagrams of them.
6.5 Effects of Aging
11. Describe a typical vertebra, the atlas
2. Explain a classification of bones and axis, and the sacrum and 19. Describe the anatomical and
based on their shapes. coccyx. physiological changes that occur in
3. Describe the anatomy of bone. 12. Name the three types of ribs and the the skeletal system as we age.
Describe long bone structure, and three parts of the sternum.
compare/contrast compact bone 6.6 Homeostasis
and spongy bone. 6.3 Appendicular Skeleton 20. List and discuss six ways the skeletal
4. Describe the physiology of bone,
13. Name the bones of the pectoral system contributes to homeostasis.
including the cells involved in growth
girdle and the pelvic girdle. Be able Discuss ways the other systems
and repair, and the process of bone
to label diagrams of them. assist the skeletal system.
growth, development, and
remodeling. 14. Name the bones of the upper limb
(arm and forearm) and the lower limb I.C.E.—In Case of Emergency
5. Name and describe six types of
(thigh and leg). Be able to label
fractures, and state the four steps in Broken Bones
diagrams that include surface
fracture repair.
features.
6. List the surface features of bones,
15. Cite at least five differences between Medical Focus
and give examples where each can Osteoporosis
the female and male pelvises.
be found. Oh, My Aching Back: Surgical Options for Back
6.4 Joints (Articulations) Injuries
6.2 Axial Skeleton 16. Explain how joints are classified, and
7. Distinguish between the axial and give examples of each type of joint. Focus on Forensics
appendicular skeletons.
17. List the types of movements that Skeletal Remains
calcitonin 8. Name the bones of the skull, and state occur at synovial joints.
Figure 10.8 the important features of each bone.
Congenital hypothyroid- 18. Explain how damage and Human Systems Work Together
ism. Individuals who have
9. Describe the structure and function degeneration occurs at joints and
of the hyoid bone. Skeletal System
hypothyroidism since how it can be treated. Outline
infancy or childhood do not
grow and develop as oth-
ers do. Unless medical
treatment is begun, the Thyroid gland
body is short and stocky. secretes 102
Developmental delay is calcitonin
into blood. Bones
also likely. take up Ca2+
from blood.
Blood Ca2+
lowers.
hig
hb
loo
dC
a 2+
er tissues incorporate so little iodine in
can also be caused by a thyroid tumor,
a lump during physical examination.
Homeostasis (normal blood Ca2+)
Accessible Writing Style More important than any other component of a
textbook, the writing must be appropriate for the level of the reader. Mader’s Under-
low
ry in combination with administration blo
od
ognosis for most patients is excellent. Ca 2+
standing Human Anatomy and Physiology features the perfect writing style for the
nificant role in both nervous conduc-
. It is also necessary for coagulation
one-semester course. It has always been written and designed for the one-semester
od calcium level is regulated in part
creted by the thyroid gland when the course, not adapted from a two-semester textbook. Paragraph introductions, explana-
tions, comparisons, and relevant, everyday examples are used with these students in
ig. 10.9). The primary effect of calci- Blood Ca2+
rises.
eposit of calcium in the bones. It does Parathyroid
the activity and number of osteoclasts.
mind. The flow of the text is logical and accessible without being overly “chatty”
glands
these cells break down bone. When release PTH
into blood.
normal, the release of calcitonin by
a low calcium level stimulates the re-
ne (PTH) by the parathyroid glands. activated
and consistently makes use of relevant examples and analogies.
vitamin D
hormone in children, whose skeleton
. By contrast, calcitonin is of minor
se parathyroid hormone is the major
parathyroid
hormone
Easy-to-Understand Art covers what’s important but leaves out unnecessary,
confusing detail.
stasis. However, calcitonin can be used (PTH)
educe the effects of osteoporosis (see
xxx). Intestines
absorb Ca2+
Kidneys
reabsorb Ca2+
Bones
release Ca2+
into blood.
Good examples of this are the homeostasis illustrations – instead of lots of
from digestive from kidney
The appendicular skeleton contains the bones of the pectoral girdle, scapula
upper limbs, pelvic girdle, and lower limbs. sternum
secretion
Pectoral Girdle rib
1 plasma
The pectoral
membrane girdle (shoulder girdle) contains four bones: two
costal
clavicles and two scapulae (Fig. 6.12). It supports the arms and cartilage
3 serves as a place of attachment for muscles that move the arms.
The bones of this girdle are held in place by ligaments and muscles. ulna
This arrangement allows great flexibility but means that the arm is radius
secretory
vesicle prone to dislocation at the shoulder joint.
incoming vesicle
a. Pectoral girdle, frontal view
2
2
Clavicles coracoid
enzyme
process
The clavicles (collarbones) are slender and S-shaped (Fig. 6.12a).
Each clavicle articulates medially with the manubrium of the ster-
Golgi apparatus acromion
3 modifies lipids and proteins
lysosome num.
from theThis is the
ER; sorts only place where the pectoral girdle is attached to
and packages process
contains digestive enzymes
that break down macromolecules the axial skeleton.
them in vesicles
entering by vesicles glenoid
proteinEach clavicle also articulates with a scapula. The clavicle cavity
serves as a brace for the scapula and helps stabilize the shoulder. It spine of
transport vesicle
transport vesicle
istakes
structurally
proteins to weak, however, and if undue force is applied to the scapula
1
takes lipids to shoulder,
Golgi apparatusthe clavicle will fracture.
Golgi apparatus
lipid
Scapulae
rough endoplasmic
smooth endoplasmic
reticulum Thereticulum
scapulae
synthesizes (sing.,
proteins and scapula), also called the shoulder blades, are
synthesizes lipids and has
various other functions Nucleus
broad bones
packages that
them somewhat resemble triangles (Figs. 6.12b and c).
in vesicles
One reason for the pectoral girdle’s flexibility is that the scapulae
ribosome b. Right scapula, posterior view
are not joined to each other (see Fig. 6.4).
Each scapula has a spine, a thick ridge of bone found on its acromion
process
a. Endocytosis
posterior surface. Note the following features as well:
b. Exocytosis
Figure 3.5 The endomembrane system. (a) Endocytosis and lysosome function. (1) A vesicle coracoid
∙ acromion process, which articulates with a clavicle and
formed by endocytosis,
process
containing macromolecules, fuses with (2) the lysosome made at the Golgi apparatus, and (3) lysosome enzymes digest the macro-
molecules in the vesicle. (b) Exocytosis and the secretory vesicle. (1) Transport vesicles from the ER bringprovides a place
proteins and lipidsof
to attachment
the for arm and upper back
muscles;
Golgi apparatus, where (2) the molecules are packaged in a secretory vesicle, which (3) travels to the plasma membrane, releasing glenoid
its contents by exocytosis.
∙ coracoid process, which serves as a place of attachment for cavity
arm and chest muscles;
∙ glenoid cavity, which articulates with the head of the arm
bone (humerus). The arm joint’s flexibility is also a result
of the glenoid cavity being smaller than the head of the
Macro to micro figures give the students an overall humerus.
48 PART I Human Organization
perspective.
Upper Limb
Visual Focus The upper limb includes the bones of the arm (humerus), the fore-
Visual Focus arm (radius and ulna), and the hand (carpals, metacarpals, and c. Right scapula, anterior view
Figure 7.3 Anatomy of a muscle 1
phalanges).
fiber. (a) A muscle
fiber contains many myofibrils with the components shown. (b) A
myofibril has many sarcomeres that contain myosin and actin fila- Figure 6.12 The pectoral girdle. (a) Frontal view of
tendon ments whose arrangement gives rise to the striations so charac- the pectoral girdles with the upper limbs attached. (b) Posterior
teristic of skeletal muscle. (c), (d) Muscle contraction
1 occurs when
deep fascia
sarcomeres contract and thin filaments slide past
The term
thick
upper extremity is used to include a clavicle and scapula (of the pectoral view of the right scapula. (c) Anterior view of the right scapula.
epimysium girdle), an filaments.
arm, forearm, wrist, and hand.
fascicle of muscle cells (fibers)
surrounded by perimysium
muscle fiber surrounded
by endomysium
myofibril 118 PART II Support, Movement, and Protection
myofilament
a. diaphysis.
that specific section is
c. periosteum.
bone.
9. Describe the structure and function of the hyoid bone.
covering.d. articular cartilage.
muscle
cell 10. Name the bones of the vertebral column and the thoracic cage. Be
b. epiphysis.
(fiber)
able to label diagrams of them.
Z line one sarcomere Z line 2. Osteons are associated with _____ bone. 11. Describe a typical vertebra, the atlas and axis, and the sacrum and coccyx.
3. Which type of bone cell breaks down bone and deposits 12. Name the three types of ribs and the three parts of the sternum.
T tubule sarcoplasmic nucleus calcium calcium into the blood?
reticulum storage site
a. osteoblast c. osteoprogenitor The skeleton is divided into the axial skeleton and the appendicular
b. A myofibril has many sarcomeres.
b. osteocyte d. osteoclast skeleton. The tissues of the axial and appendicular skeletons are
6,0003
myosin head bone (both compact and spongy), cartilage (hyaline, fibrocartilage,
4. The region in a long bone where growth occurs is
thick
the ____________.
and elastic cartilage), and dense connective tissue, a type of fibrous
filament
connective tissue. (The various types of connective tissues were
5. Imagine that an artery has to pass through bone to enter the
thin
filament extensively discussed in Chapter 4.)
skull. What is the feature through which the artery will pass?
Z line
H zone
A band I band (Refer to Table 6.1.)
In Figure 6.4, the bones of the axial skeleton are colored gray,
c. Sarcomeres are relaxed. d. Sarcomeres are contracted. and the bones of the appendicular skeleton are colored tan for easy
Answers in Appendix A.
distinction. Notice that the axial skeleton lies in the midline of
the body and contains the bones of the skull, the hyoid bone, the
Myofibrils and Sarcomeres stripes, or striations, of skeletal muscle fibers are formed by the
Myofibrils are cylindrical and run the length of the muscle fiber. placement of myofilaments within the sarcomeres. A sarcomere
Each myofibril is composed of numerous sarcomeres, which are contains two types of protein myofilaments: The thick filaments
microscopic repeating units (Fig. 7.3). Each sarcomere extends are made up of a single protein called myosin. Thin filaments are
between two dark, vertical lines called Z lines. The horizontal made up of three proteins: a globular protein called actin, Skull:
plus Skull:
frontal bone
parietal bone
Chapter 7 The Muscular System
zygomatic
137 bone
temporal bone xi
maxilla occipital bone
mandible
hyoid bone
clavicle
Pectoral girdle: scapula
clavicle
humerus
scapula
lon96431_fm_i-xx.indd 11 Rib cage: vertebral column 19/11/15 5:20 PM
Sphenoid Bone The sphenoid bone helps form the sides and floor Nasal Bones The two nasal bones are small, rectangular bones
of the cranium and the rear wall of the orbits. The sphenoid bone that form the bridge of the nose (see Fig. 6.5). The anterior distal
is shaped like a butterfly. Its complex shape allows it to articulate portion of the nose is cartilage, which explains why the nose is not
with and hold together the other cranial bones (Fig. 6.7). Within seen on a skull.
the cranial cavity, the sphenoid bone has a saddle-shaped midpor-
tion called the sella turcica (Fig. 6.7b), which houses the pituitary Vomer Bone The vomer bone joins with the perpendicular plate of
gland in a depression. the ethmoid bone to form the nasal septum (see Figs. 6.5 and 6.6a).
a. diaphysis.
abduction (ăb-dŭk9shŭn), p. 124 fontanel (fŏntŭh-nĕl9), p. 110
c. periosteum.
foramen magnum (fŏr-ā9-mĕn măg9nŭm), p. 110
rotation (rō-tā9shŭn), p. 125
sacrum (sā9krŭm), p. 116
9. Describe the structure and function of the hyoid bone.
adduction (ăd-dŭk9shŭn), p. 124
amphiarthrosis (ămfē-ăr-thrō9sĭs), p. 123 gliding joint (glīd9ĭng jōynt), p. 124 saddle joint (săd9ĕl jōynt), p. 124
10. Name the bones of the vertebral column and the thoracic cage. Be
Bones ofb.the epiphysis. d. articular cartilage. Begin Thinking
diagrams Clinically
hard palate (hărd păl9ut), p. 113 scapulae (skăp9yŭh-lā), p. 118
Face
appendicular skeleton (ăpĕn-dĭk9yū-lĕr
skĕl9ĕ-tŭn), p. 110 hematopoiesis (hēmăh-tō-pōy-ĕ9sĭs), p. 103 sella turcica (sĕl9ŭh tŭr9sĭk-ŭh), p. 113 able to label of them.
2. Osteons are associated with _____ bone.
appositional growth (ăpŭh-zĭsh9ŭn-ŭl grōth), hinge joint (hĭnj jōynt), p. 124 sinus (sī9nŭs), p. 110
11.
Maxillae The two maxillae form the upper jaw. Aside from con-
p. 107
articular cartilage (ăr-tĭk9yū-lĕr kăr9tĭ-lĭj), p. 103
humerus (hyū9mŭr-ŭs), p. 119
ilium (ĭl9ē-ŭm), p. 120
spongy bone (spŭnj9ē bōn), p. 103
sternum (stŭr9nŭm), p. 116
You’re treating an 11-year-oldthe
Describe a typical vertebra, atlas and
patient in axis, and the sacrum and coccyx.
the emergency
12. Name the three types of ribs and the three parts of the sternum.
tributing3.toWhich type of
the floors of bone cell breaks
the orbits
atlas (ăt-lŭhs), p. 115 and to down boneofand
the sides
articulation (ăr-tĭkyū-lā9shŭn), p. 103
the deposits
floor of
intervertebral disk (ĭntĕr-vĕr9tĕ-brŭl dĭsk), p. 113
intramembranous ossification (ĭntrŭh-
room. His right eye was struck by a baseball bat, and he’s
supination (sūpĭ-nā9shŭn), p. 125
suture (sū9chĕr), p. 110
calcium into the blood? rapidly developing a nasty black eye. What bones might
the nasal cavity, each maxilla has the following processes:
axial skeleton (ăk9sē-ăl skĕl9ĕ-tŭn), p. 109 mĕm9brān-ŭs ŏsŭ-fĭ-kā9shŭn), p. 105 synarthrosis (sĭn-ăr-thrō9sĭs), p. 123
axis (ăk9sĭs), p. 115 inversion (ĭn-vĕr9zhŭn), p. 125 synovial fluid (sĭ-nō9vē-ăl flū9ĭd), p. 123
a. osteoblast
ball-and-socket joint (băwl and sŏk9ĭt
jōynt), p. 124
c. osteoprogenitor
ischium (ĭs9kē-ŭm), p. 120
ligament (lĭg9ŭh-mĕnt), p. 123
Thebeen
have skeleton is divided
broken into the axial skeleton and the appendicular
by the injury?
synovial joint (sĭ-nō9vē-ăl jōynt), p. 123
synovial membrane (sĭ-nō9vē-ăl mĕm9brān), p. 123
∙ alveolar process (Fig.
bony pelvis (bō9nē pĕl9vĭs), p. 120
b. osteocyte 6.6a). The alveolar processes contain
medullary cavity (mĕd9ū-lārē kăv9ĭ-tē), p. 103
d. osteoclast skeleton. The tissues
talus (tă9lŭs), p. 123 of the axial and appendicular skeletons are
bursae (bŭr9sā), p. 123 menisci (mĕ-nĭs9kī), p. 123
Answer and discussion in Appendix A.
tarsal bones (tăr9sŭl bōns), p. 123
the tooth sockets for teeth: incisors, canines, premolars, and
calcaneus (kăl-kā9nē-ŭhs), p. 123 metatarsal bones (mĕt9ŭh-tăr9sŭl bōnz), p. 123
bone (both compact and spongy), cartilage (hyaline, fibrocartilage,
temporal process (tĕm9pō-rŭl prŏh9sĕs), p. 113
4. The region in a long bone where growth occurs is
cartilaginous joints (kăr9tŭl-ăj9ŭh-nŭs jōyntz), p. 123 occipital condyle (ŏk9sĭp-ĭ-tŭl kŏn-dīl), p. 110 tibia (tĭb9ē-ŭh), p. 121
molars.
circumduction (sĕrkŭm-dŭk9shŭn), p. 124 ossification (ŏs99ĭ-fĭ-kā9shŭn), p. 105
and elastic cartilage), and dense connective tissue, a type of fibrous
ulna (ŭl9nŭh), p. 119
the ____________.
clavicles (klăv9ĭ-kŭls), p. 118 osteoblast (ŏs9tē-ō-blăst),
occipital bone, twop. 105
temporal C. The (vĕr9tŭh-brā),
vertebrae pelvic girdle p. contains
113 two VI. Homeostasis
∙ palatine process (Fig. 6.7a). The left and right palatine pro-
coccyx (kŏk9sĭks), p. 116 bones,
osteoclast one sphenoid
(ŏs9tē-ō-klăst),
one(ŏs9tē-ō-sīt),
ethmoid bone.
bone, and
p. 105
The facial connective tissue. (The various types of connective tissues were
coxal
vertebral bones,
column and formskŏh9lŭm),
(vĕr9tĕ-brăl
vis when joined to the sacrum
the pel- p. 113 A. The bones protect the internal
organs: The rib cage protects the
5. Imagine that an artery has to pass through bone to enter the Hyoid Bone
compact bone (kŏm9păkt bōn), p. 103 osteocyte p. 105
cesses form the anterior portion of the hard palate (roof of osteon bones
extensively discussed in Chapter 4.)
condyloid joint (kŏn9dīl-ōyd jōynt), p. 124 include
(ŏ9stē-ŏn), p. 103two maxillae, two and coccyx.
Clinical Key Terms The female pelvis is heart, lungs, and kidneys; the skull
palatine bones, two zygomatic generally wider and more shal- protects the brain; and the verte-
skull. What is the feature through which the artery will pass?
coxal bone (kŏk9săl bōn), p. 120 osteoprogenitor cells (ŏstē-ō-prō-jĕn9ĭ-tŭr
bones, two lacrimal bones, two arthritis (ăr-thri9 tĭs), p.
low than the male pelvis.126 brae protect the spinal cord. The
the mouth). In Figure
hyoid6.4, the(see
bonesFig.of6.4)
the is
axial skeleton are colored
to the gray,
depression (dĭ-prĕsh9ŭn), p. 125 sĕlz), p. 105
The U-shaped bone located superior
nasal bones, the vomer bone, bursitis
D. The (bŭr-sī9tĭs),
lower limb p. 123
contains the femur, bones assist all phases of respira-
(Refer to Table 6.1.)
diaphysis (dī-ăf9ĭ-sĭs), p. 103 patella two
(pŭh-tĕl9 ŭh),nasal
inferior p. 121conchae, and fracturethe(frăk9chĕr),
patella, the p.tibia,
108 the fibula, tion. The rib cage assists the
Palatine
elevation (ĕlŭh-vā9shŭn), p. 125
Bones
Answers The two palatine
in Appendix A.
B. girdle
pelvic The U-shaped hyoid bone
(pĕl9vĭk gĕr9dŭl),
bones contribute to the floor and
cated in p.
pelvis (pĕl9-vĭs), the120
p. 120is lo-
neck. It anchors the
larynx (voicesals,disk
herniated metatarsals,
It
(hĕr9nē-ā-tĕd
IV. Joints (Articulations)
Is the only
and phalanges).
bone
dĭsk), p. 114 in the body that
marrow produces the red blood
cells that transport oxygen. The
distinction. Notice that the with
axialanother
skeleton liesInstead,
in the midline of
endochondral ossification (ĕndō-kŏn9drŭl kyphosis (kī-fō9sĭs), p. 114
ŏsŭh-fĭ-kā9shŭn), p. 105
lateral wall of the nasal cavity (Fig. 6.5). The horizontal plates of
epiphyseal plate (ĕpĭ-fĭz9ē-ăl plāt), p. 106
tongue
periosteum and does not p.
(pĕrē-ŏs9tē-ŭm),
with any other bone.
phalanges (fŭh-lăn9jēz), p. 123
articulate
103
does not articulate
lordosis (form
tween(lŏr-dō9sĭs),
bones. Theya joint)
Joints are regions of articulation be-
p. 114
are classified ac- bone. it is
bones store and release calcium.
Calcium ions play a major role in
the body and contains the bones of the skull, the hyoid bone, the
C. The typical vertebra has a body, mastoiditis (măstōy-dī9tĭs),
cording to their structure and/or p. 110 muscle contraction and nerve
epiphysis (ĕ-pĭf9ĭ-sĭs), p. 103
the palatine bones form the posterior portion of the hard palate
eversion (ē-vĕr9zhŭn), p. 125
pivot joint
pronation
(pĭv9ŭt jōynt),
a vertebral arch p.
(prō-nā9shŭn),
vertebral foramen,
124
surrounding
p. and
the
125 a spinous
suspended from
osteoarthritisthe styloid
degree of movement. processes
(ŏstē-ō-ăr-thri9
are typically(ŏstē-ō-pō-rō9sĭs),
osteoporosis
Fibrous
immovable, cartilagi-
tĭs), p. temporal
126
joints
p. 107
bones by
conduction. Calcium ions also
help regulate cellular metabolism.
extension (ĕk-stĕn9shŭn), p. 124 process. The
pubic symphysis first two
(pyū9bĭk vertebrae
sĭm9fĭ-sĭs),
the stylohyoid muscles and ligaments. It anchors the tongue and
p. 120 nous joints are generally
reduction (rĭ-dŭk9shŭn), p. 108 slightly The bones assist the lymphatic
(Fig. 6.7a).
femur (fē9mŭr), p. 121 are the atlas
pubis (pyū9bĭs), p. 120and axis. The verte-
End of Chapter
movable, and synovial joints usually
rheumatoid arthritis (RA), p. 126
system and immunity. Red bone
illae (i.e.,Summary
the palatine processes)
geal vertebrae. Cervical,
and (2) horizontal plates of the with swallowing.their sockets. gestion. The bones used for
thoracic, and lumbar vertebrae
are separated by intervertebral organized with the Summary updated for
B. Cartilaginous joints occur where
bones are connected by hyaline
chewing break food into pieces
small enough for chemical diges-
palatine I.bones. A
Skeleton: Overview cleft
Skull:palateD. results
A. The skeleton supports and pro-
disks.
The aribmedullary
racicmarrow
when
cavitythe
cage contains
andribs
with
is bounded
either
yellow
tho-
by com-
(1) or (2) have C. The
Skull: jointssurface
every chapter. Key terms are divided into basic
or fibrocartilage.
C. different
Table 6.1kinds describes
are ball features
of synovialthe different
of bones.
tion. The skeleton is necessary for
locomotion. Humans have a
process.
scapula.
bone.
and the
osteoblasts build
A zygomatic arch, the
elevation,
every chapter.
and depression).
The cranium includes the frontal
of fibrocartilage called the intervertebral disks (Fig. 6.8). The
D. The most bone,common typesbones,
two parietal of ar- one
crine system regulates calcium
storage and growth of bones.
B. The upper limb contains the thritis are osteoarthritis, rheuma- 14. Whatsystem
The cardiovascular are thetrans-
bones of the lower limb? 16. How can joint movements permitted 18. What functions of the skeletal system
Pectoral girdle:
phalanges). on the skeletal system are arthritis
and osteoporosis. scapula
of each type of joint. (pp. XXX–XXX) 17. How does aging affect the skeletal sys-
tem? (p. XXX)
clavicle
humerus
Learning Outcome Questions
scapula Study Questions
I. Match the items in the key to the Chapter 6 The Skeletal
e. olecranon process girdleSystem
is specialized 113
Rib cage: vertebral column
1. What are five functions of the skeleton? 6. List the bones of the axial and appen- 10. What are the bones bonesof the listed in questions 1–6.
pectoral f. acetabulum for ________.
(p. XX) dicular skeletons. (p.103 and Fig. 6.4, girdle? Give examples Key:to demon- g. greater and lesser trochanters 19. The term phalanges is used for the
sternum2. What are five major categories of p. XXX) strate the flexibility of thea. pectoral
forehead 7. scapula bones of both the ________ and
bones based on their shapes? (p. 98) 7. What are the bones of the cranium and girdle. What are the special b. chin
features 8. sternum the ________.
c. cheekbone 20. The knee is a freely movable (syno-
ribs 3. What are the parts of a long bone?
What are some differences between
the face? Describe the special features
of the temporal bones, sphenoid bone,
of a scapula? (p. XXX)
d. elbow
11. Name the bones of the upper limb,
9.
10.
femur
temporal bone vial) joint of the ________ type.
e. shoulder blade 11. coxal bone
costal cartilages
compact bone and spongy bone? and ethmoid bone. (pp. XXX–XXX) then outline the special features of
f. hip
IV. Match the movement with the descrip-
ulna
(pp. XX–XX) 8. What are the parts of the vertebral col- these bones. (pp. XXX–XXX) 12. ethmoid bone tion in questions 21–25.
g. leg 13. ulna
4. How does bone grow in children, and umn, and what are its curvatures? Dis- 12. What are the bones of the pelvic girdle, a. extension
how is it remodeled in all age groups? tinguish between the atlas, axis, 1. temporal
and what are their functions? (p. XXX) and zygomatic bones b. circumduction
Pelvic girdle: (pp. XXX–XXX) sacrum, and coccyx. (pp. XXX–XXX) radius
2. tibia and fibula
13. What are the false and true pelvises,
3. frontal bone
III. Fill in the blanks.
14. Long bones are ________ than c. adduction
5. What are the various types of frac- 9. What are the bones of the rib and what are several differences they are wide. d. flexion
coxal bones tures? Outline the four steps that are cage? List several functions of the rib
4. ulna
between the male and female pel-
5. coxal bone
15. The epiphysis of a long bone con- e. abduction
21. moving a body part toward the
required for fracture repair. (p. XXX) cage. (pp. XXX–XXX) vises? (p. XXX)
carpals
6. scapula
tains ________ bone, where red
blood cells are produced. midline
22. moving a body part away from the
sacrum II. Match the items in the key to the
metacarpals
bones listed in questions 7–13.
16. The ________ are the air-filled
spaces in the cranium. midline
131 23. moving a body part in a circle
coccyx
Chapter 6 The Skeletal
Key: System 17. The sacrum is a part of the
a. external acoustic meatus ________, and the sternum is a 24. decreasing the angle of a joint
b. cribriform plate part of the ________. 25. increasing the angle of the joint
c. xiphoid process 18. The pectoral girdle is specialized
phalanges d. glenoid cavity for ________, while the pelvic
opments in applied aspects of anatomy and physiol- joints, and muscles about the present position of body parts.
tau that causes neurofibrils to tangle—are known to be involved in
a loud sound). The word pons means “bridge” in Latin, and
the disease process. However, hundreds of questions about the pro-
described in the Chapter 4 opening reading). Next, these cells were
successfully grown in a gel medium, where they formed three-
It also receives motor output from the cerebral cortex about true to its name, the pons contains bundles of axons traveling
ogy to important concepts in the text. Examples where these parts should be located. After integrating this in-
cess remain. Why do some people form the proteins, but show no
signs of disease? Does plaque formation cause tangle formation?
between the cerebellum and the rest of the CNS. In addition, the
dimensional neural networks, much like those of a human brain.
Researchers then induced the same gene mutations found in auto-
Do the proteins themselves cause the disease symptoms, or do they somal dominant Alzheimer disease (ADAD). For the first time, the
include “Novel Stent for the Severest Strokes,” “Brainformation, the cerebellum sends motor signals by way of the pons functions with the medulla oblongata to regulate breath-
result when the immune system destroys damaged cells? Why do neurons grown in these cell cultures formed complex networks
brain stem to the skeletal muscles. In this way, the cerebel- ing rate. specific mutations always doom some people to die from the dis- that showed the two distinct pathological changes of Alzheimer
in a Petri Dish: A Human Model for Alzheimer lum maintains posture and balance. It also ensures that all of
ease? Why does disease risk increase with age? To date, research
The medulla oblongata contains a number of reflex cen-
into these and other questions has used mice equipped with human
disease: first, amyloid plaques and then the resulting neurofibril-
lary tangles. Thus, this cell culture technique has created a power-
the muscles work together to produce smooth, coordinated ters for regulating heartbeat, breathing, and vasoconstriction.
Research,” “Improvements in Transfusion Technology,”
Alzheimer genes as the mammalian study model. However, this ful new research tool: a working reproduction of an “Alzheimer
type of study has had serious limitations. Obviously, mice aren’t brain” in a petri dish. Scientists hope that having this replica will
voluntary movements. In addition, the cerebellum assists the It also contains the reflex centers for vomiting, coughing,
humans. The animal brains grow amyloid plaques, but not the allow possible drugs for Alzheimer disease to be rapidly tested. In
“Necrotizing Fasciitis,” and “Influenza: A Constant learning of new motor skills, such as playing the piano or hit- sneezing, hiccupping, and swallowing. The medulla oblongata
resulting neurofibrillary tangles seen in human brains. Further,
experimental drugs that cured mice failed to show any benefits in
addition, this 3-D neural network “brain” could also be used to
investigate other neurodegenerative disorders such as Parkinson’s
ting a baseball. lies just superior to the spinal cord, and it contains tracts that
Threat of Pandemic.” The Focus on Forensics and humans.
ascend or descend between the spinal cord and higher brain
disease.
centers.
I.C.E.: In Case of Emergency readings engage stu- The Brain Stem The entire brain stem is critically important for control of the
dents in real-life scenarios that challenge them to use,
The brain stem is the structure that joins the
Limbic System upper brain re- parasympathetic division of theof autonomic
Stimulation motor
different areas of nervous
the limbic system.
system causes
subject to experience rage, pain, pleasure, or sorrow. By causing
the
gions to the spinal cord. The brain stem contains
The limbic the mid-
system (illustrated in purple in Cranial nerves
the following figure) whose neuron cell bodies are found in this area
and expand upon, their recently acquired knowledge. brain, the pons, and the medulla oblongata (see
is a collection Fig. 8.8a).
of structures travel and
from both the cerebrum to the
thedien-
cephalon. It lies just inferior to the cerebral cortex and contains
pleasant or unpleasant feelings about experiences, the limbic sys-
eyes, tem
facial glands,
apparently guidesand internal
the individual intoorgans in isboth
behavior that likely the
to
Running through all of these structuresneural
is a pathways
web ofthat gray matter
connect portions of thethorax
cerebral and
cortexabdominopelvic
and regions.
increase the chance of survival.
The limbic system is also involved in learning and memory.
called the reticular formation. The midbrain
the temporal acts as the
lobes with a thalamus
relay and the hypothalamus:
The reticularInformation assists
particular, the most thestructure
inferior cerebellum in system,
of the limbic main-
station for tracts passing between the cerebrum and the spi- taining muscle tone; the it also assists
hippocampus, theinpons
is vital and ofmedulla
processing short-termin regu-
memory
to become long-term memory. Learning requires memory, and
nal cord or cerebellum. It also has reflex centers for visual, lating respiration, memory
heart israte,
storedand
in theblood
sensorypressure.
regions of theThe sensory
cerebrum, but
thalamus just what permits memory development is not definitely known.
The involvement of the limbic system in memory explains why
emotionally charged events result in our most vivid memories.
The fact that the limbic system communicates with the sen-
sory areas for touch, smell, vision, and so forth accounts for the
hypothalamus ability of any particular sensory stimulus to awaken a complex
The Cerebellum
MEDICAL FOCUS Traumatic Brain Injury
hippocampus The cerebellum is separated from the brain stem by the
fourth ventricle (see Fig. 8.8a). The cerebellum has two
hemispheres, which are joined by a narrow median portion.
Research on Alzheimer Disease: Causes, Treatments, Prevention, and Hope for a Cure Each portion is primarily composed of white matter, which
In March 2009, Natasha Richardson, actress and wife of actor Liam Patients who have had a concussion
in longitudinal should
section has always
a treelike be examined
pattern. Overlying the
Alzheimer disease (AD) is an irreversible, fatal disorder characterized Alzheimer cell protein is another possible avenue Neeson, lost At
for research. consciousness
this while she was on the beginner slope of a by an emergency room physician to rule out a critical injury. Before
by a gradual loss of reason that begins with memory lapses and ends with MontrealOneskicategory,
time, only five drugs are accepted for disease treatment. resort, after a seemingly minor fall. After regaining con- first responders transport the person to the hospital, they should
the inability to perform any activities. Personality changes such agitation cholinesterase inhibitors (Aricept®, Razadynesciousness,
®
, Exelon®, Reminyl ®
),
she insisted that she was fine, even
178 turning
PART III away EMS
Integration per-
and Coordination quickly assess whether the patient is alert and able to respond to per-
and hostility, and memory deficits that affect daily routines often signal works at neuron synapses in the brain, slowing the activity of the enzyme
the onset of AD. For example, a normal 60- to 70-year-old might forget
sonnel. However, she complained of a severe headache hours later, and
that breaks down acetylcholine (ACh). Allowing ACh to accumulate in
son, place, and time—in the language of the emergency room, “ori-
the name of a friend not seen for years, but someone with AD forgets the synapses keeps memory pathways in the brainher condition
functional rapidly deteriorated. After being declared brain dead,
for a longer ented times three.” The individual should be able to identify himself
®
name of a neighbor who visits daily. Likewise, a healthy senior might period of time. The newest drug, memantine (NamendaRichardson ), blocksdied in a New York hospital two days later.
excito- (person), tell where he is (place), and correctly name the day of the
forget where he placed his car keys, while a person with AD will forget toxicity: the tendency of diseased neurons to self-destruct. This medicamedica-
Richardson’s accident focused attention on the need for immedi- week (time). Next, the victim’s pupillary reflex is tested to ensure that
what those keys are for. People afflicted with AD become confused and tion is used only in moderately to severely affected patients. Using the
tend to repeat the same question. Signs of mental disturbance eventually drug allows neurons involved in memory pathways ate medical attention
to survive longer in when a traumatic brain injury (TBI) is suspected. both pupils react similarly and quickly in response to light. Emergency
appear, and patients gradually become bedridden and die of a complica- affected patients. However, it’s important to note Traumatic brain ofinjuries cause swelling of the brain and meninges,
that neither category care providers and family members must be aware of the signs of brain
tion, such as pneumonia. At the cellular level, AD is characterized by the medication cures AD. Both merely slow the progress of disease symp symp-
which reduces blood supply to the brain. Concussion is often the first damage: severe headache, nausea and vomiting, slow heartbeat and
presence of abnormally structured neurons and a reduced amount of the toms, allowing the patient to function independently for a longer period
neurotransmitter acetylcholine (see p. xxx). These defective neurons are of time. Additional research is currently underway symptom
to test theofeffective
TBI. Patients who suffer a concussion become dizzy, con-
effective- breathing rate, and decreasing consciousness. In babies and small chil-
especially seen in the portions of the brain involved in reason and mem- fused or disoriented,
ness of anticholesterol statin drugs, as well as anti-inflammatory medica- suffer short-term memory loss, or lose conscious-
medica dren, the early signs of TBI include crying inconsolably and refusal to
ory. The AD neuron has two pathological features. The first consists of tions, in slowing the progress of the disease. ness. Bleeding inside the brain or skull, called hematoma, or bruising nurse or eat. In these situations, immediate medical and surgical treat-
bundles of fibrous protein, called neurofibrillary tangles, which surround
Research on Prevention of the brain, called a contusion, may follow concussion. These are ment will hopefully lessen or prevent brain damage.
the nucleus in the cells. The tangles are due to an abnormal form of tau, a
protein molecule that normally helps to stabilize microtubules that form Much of current research on AD focuses on prevention. Early findings
life-threatening and often fatal injuries that may not be immediately Athletes (and their parents and coaches) must be aware that no con-
the cell’s cytoskeleton. In addition to these tangles, protein-rich accumu- have shown that risk factors for cardiovascular disease—heart attacks and
evident, but develop in the hours to days after the initial loss of con-
stroke—also contribute to an increased incidence of AD. These include
cussion should be considered minor; each is a traumatic brain injury. Fur-
lations, called amyloid plaques, envelop the axon branches. Over time,
affected neurons will die. The cortex and hippocampus shrivel, the brain
sciousness. In seden- Richardson’s case, her fall resulted in an epidural
elevated blood cholesterol and blood pressure, smoking, obesity, seden Ms. ther, repeated concussions in young people can result in permanent brain
shrinks in volume, and the ventricles become enlarged. tary lifestyle, and diabetes mellitus (see Chapterhematoma: bleeding between the skull and dura mater. Had she re-
12). Low-level infection damage and predispose the victim to neurodegenerative diseases, includ-
caused by gum disease has also been shown to increase the probability of
Research Regarding Its Causes ceived prompt medical treatment, the hematoma could have been sur- ing Alzheimer and Parkinson’s disease. Under no circumstances should an
developing heart disease, and by extension, Alzheimer disease. Thus,
As techniques for genetic study continue to improve, several genetic muta- gically
evidence suggests that a lifestyle tailored for good repaired.
cardiovascular health athlete be returned to play in that day’s game following a concussion.
tions specific to Alzheimer have been identified. One set, designated by may also prevent AD. Slight changes in diet may also lessen the threat of
the acronyms APP, PS1, and PS2, are termed deterministic. People who developing AD: boosting vitamins B and D, eating fatty fish such as
inherit one of these three mutated genes will always develop the disease, salmon, and drinking coffee. Further, younger people must try to prevent
called autosomal dominant Alzheimer disease (ADAD). It’s interesting to blows to the head. It’s been shown that head injuries (such as those expe-
expe
note that APP, the first of these defective genes to be discovered, is found
on chromosome 21. Down syndrome results from the inheritance of three
rienced by football players) can increase the risk of developing AD in
later life 19-fold. Wearing seat belts and helmets and taking steps to pre-
FOCUS on FORENSICS
copies of chromosome 21, and people with Down syndrome tend to vent falls are commonsense, easy ways to prevent head injury. Finally, Chapter 8 The Nervous System 179
develop AD. (You will learn more about autosomal dominant disorders in staying mentally, physically, and socially active—as long as possible— Retinal Hemorrhage in Shaken Baby Syndrome
Chapter 19.) Mutation of a fourth gene, designated APO, puts patients at will help to slow the course of mental impairment for AD sufferers.
risk but does not always result in disease. Scientists are now studying vic-
tims with mutations to try to discover the exact cause for the disease. Early Detection and Hope for a Cure It’s one of the fastest-growing epidemics in children in North One key to making a correct diagnosis of SBS is a retinal exam.
Recent findings have led researchers to believe that the neuron deteriora- Currently, researchers are testing vaccines for AD that would target the America, and the fifteenth-leading cause of death to young children— The retina is a highly vascular tissue with a complex system of blood
tion seen in Alzheimer disease patients may be caused by the spread of the patient’s immune system to destroy amyloid protein. Early study results
child abuse. Approximately 1,600 American children die every year vessels. A healthy retina shows distinct blood vessels in a lacy net-
tau protein from one cell to the next, much as a virus is spread from one show some promising outcomes of this treatment in early-stage patients.
at the hands of a parent or other caregiver, and 75% of those fatalities work. The retina of an infant with SBS shows irregular, blotchy areas
infected cell to another. Other studies have implicated a second protein, However, scientists believe that curing AD will require an early diagnosis
because it’s thought that the disease may begin in the brain 15 to 20 years occur in children four years old or younger. In babies up to a year old, of hemorrhaged blood. Evidence of retinal hemorrhage should
striatal-enriched tyrosine phosphatase, or STEP, in the cell destruction
found in Alzheimer sufferers. Further, other investigators are exploring the before symptoms ever develop. At present, diagnosis can’t be made with the leading cause of child abuse death is a phenomenon called “shaken always lead to suspicion of abuse—this injury does not occur in a
role of cell lysosomes in AD, suspecting that these essential organelles absolute certainty until the brain is examined at autopsy. In the future, baby syndrome,” or SBS. As the name implies, the affected infant has typical accidental fall.
may be failing to destroy the abnormal proteins found in diseased cells. cerebrospinal fluid testing may allow amyloid proteins to be detected been shaken violently by a caregiver. As little as 5 seconds of violent Studies of adult abusers have shown that child abuse is rarely
before disease symptoms appear. Researchers are also developing ways shaking can permanently injure or kill a baby. premeditated; the adult simply loses control while trying to stop a
Research into Its Treatment to tag the amyloid protein with radioactive molecules, which will allow Shaking an infant produces the same effect as whiplash in an particular behavior, such as excessive crying. Because adult caregiv-
Each new finding about what causes Alzheimer disease creates new pos- detection of the protein using a PET scan. (You learned about PET and adult because an infant’s head is very large in proportion to the rest of ers routinely deny involvement in a child’s injury, health-care workers
sibilities for its treatment as well. Researchers are now conducting clini- other imaging techniques in Chapter 1.) The Medical Focus reading in
cal testing on antibodies that block cell-to-cell transmission of the tau
its body and the neck muscles are weak. However, in the infant the must be vigilant and observant to detect and stop SBS. Unexplained
Chapter 9 describes an eye scan technique that might allow an earlier
protein. (You can read more about antibodies in Chapter 13.) A second whiplash effect occurs over and over. Like an adult whiplash injury, a drowsiness, unconciousness, or seizures in an infant should always be
diagnosis, and the What’s New reading on page XXX describes an
treatment might involve the creation of drugs that block formation of the exciting breakthrough in cell culture that will create new options for shaken baby’s brain slams back and forth inside the skull. This investigated with an eye exam, using eye drops to dilate the pupil and
STEP protein. Boosting lysosomal degradation of the abnormal studying neurons and drug therapies in the laboratory. extreme force damages nerve tissue and tears delicate blood vessels examine the retina.
throughout the brain and in the eyes.
9.4 Sense of Hearing which extends from each middle ear to the nasopharynx (area at
the back of the throat, which joins the nasal cavity), allows us to
10. Detail the anatomy of the ear, and give a function of each part.
equalize air pressure. Chewing gum, yawning, and swallowing in
11. Describe the sensory receptors for hearing and their mechanism
of action. elevators and on airplanes help to move air through the auditory
tubes upon ascent and descent. As this occurs, we often hear our
The ear has two sensory functions: hearing and equilibrium (bal- ears “pop.”
ance). The sensory receptors for both of these are located in the inner The inner ear lies in the bony labyrinth, a delicately carved
cavity within the temporal bone of the skull. Lining the bone is
xiii
ear, and each consists of hair cells with stereocilia (long micro-
villi) that are sensitive to mechanical stimulation. The hair cells are a tube of tissue called the membranous labyrinth. Two distinct
mechanoreceptors, which respond to pressure or body movement. fluids are found in the inner ear: The space between the bony
labyrinth and the membranous labyrinth contains perilymph (a
fluid similar to cerebrospinal fluid) and the membranous laby-
Anatomy and Physiology of the Ear rinth is filled with endolymph. The inner ear is divided into three
Figure 9.12 shows that the ear has three divisions: outer, middle, areas: the semicircular canals, the vestibule, and the cochlea. The
and inner. The outer ear consists of the pinna (external flap) and semicircular canals and the vestibule are both concerned with
lon96431_fm_i-xx.indd 13 the external auditory canal. The opening of the auditory canal is equilibrium and the cochlea is involved with hearing. The 19/11/15
cochlea 5:20 PM
lined with fine hairs and sweat glands. Modified sweat glands are resembles the shell of a snail because it spirals.
Changes to This Edition
Each chapter contains updated and improved line art and new, ∙ New Reading: What’s New: 3-D Printing to Create
more current photos. Images from McGraw-Hill Education’s Complex Tissues.
award-winning interactive learning software, Anatomy and Phys- ∙ Updated the story of Henrietta Lacks, the subject of the
iology REVEALED®, have been incorporated throughout the text. chapter introduction. Her gravesite has recently been located,
All information regarding signs, symptoms, diagnosis, and and after many decades has been permanently identified with
treatment of disease has been carefully investigated using Up To an appropriate grave marker.
Date®, a professional peer-reviewed overview of current research in ∙ Based on heat map analysis, revised description of epithelial
each respective field. This service is utilized throughout the nation
tissues to make it more complete.
by many universities and hospitals, including the Mayo Clinic.
Each section of a chapter ends with a Content Check-Up!
to test student knowledge. In response to reviewer requests, Chapter 5:
selected Content Check-Up! questions throughout the chapters
have been replaced with higher-level questions requiring critical ∙ New chapter opener, featuring new photos.
thinking and assimilation of ideas. ∙ Per reviewer request, relocated and revised the section on
Functions of the Skin.
Chapter 1: ∙ Completely revised sections on homeostasis to improve
readability.
∙ Updated Medical Focus: Imaging the Body to include latest ∙ Based on heat map analysis, revised description of sebaceous
technologies used for imaging, including functional magnetic gland function.
resonance imaging and diffusion tensor imaging.
∙ Based on heat map analysis, revised descriptions of
temperature regulation.
Chapter 2:
∙ New chapter opener about toxins as medication, with new Chapter 6:
photographs.
∙ New artwork throughout, incorporating multiple images from
∙ Updated Medical Focus: Prions: Malicious Proteins? to
Anatomy and Physiology REVEALED®.
incorporate latest diagnostic technology.
∙ Updated Medical Focus: Osteoporosis to reflect state-of-
∙ Updated Medical Focus: The Deadly Effects of High-Level
the-art knowledge about medical research in the field.
Radiation to contain current information regarding the
∙ Reviewed current findings on causes and therapies to update
effects of radiation on cell-cell junctions.
Medical Focus: Oh, My Aching Back—Options for Back
∙ In response to reviewer commentary: revised explanations
Injuries.
for mass number; low levels of radiation; atomic structure,
∙ Based on heat map analysis, revised description of lacunae
ionization, buffers.
and canaliculi.
∙ Based on heat map analysis, revised discussion of dehydration
∙ Based on heat map analysis, revised description of transverse
reaction, cation and anion structure, disaccharides, glycogen
foramina.
storage, phospholipid cell membrane structure, protein
function.
Chapter 7:
Chapter 3: ∙ Completely reworked Figure 7.6.
∙ Based on heat map analysis: revised description of chromatin ∙ Researched current findings and professional recommendations
and chromosomes, simple diffusion. to overhaul Medical Focus: Benefits of Exercise. The article
features a table of practical, real-world recommendations about
incorporating exercise into daily living.
Chapter 4: ∙ Based on reviewer feedback, updated discussion of all-or-
∙ Updated What’s New: Targeting the Traitor Inside, which none law, recruitment, muscle tone.
now features the most current available information ∙ Based on reviewer feedback, updated discussion of twitch,
regarding cancer therapies. tetanus, fatigue.
xiv
xv
xvi
xvii
Required=Results
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PART I
R ecognize anything familiar? The little face, chest, and hands shown here
belong to a baby in the womb, detailed using ultrasound, one of several
imaging techniques described on page 16. All modern imaging methods have
evolved from simple two-dimensional X rays, invented in 1895. The three-
dimensional ultrasound procedure used to create this photo reveals structures
with great detail and clarity. Ultrasound technology can monitor the infant’s
development and help to ensure a safe delivery for baby and mother. It can
even enable physicians to diagnose fetal abnormalities and treat the baby
while still in the womb!
Learning Outcomes After you have studied this chapter, you should be able to:
1.1 The Human Body 1.3 Body Cavities and Membranes 8. Describe in general the functions of
each organ system.
1. Define anatomy and physiology, and 4. List the cavities of the body, and
explain how they are related. state their locations.
1.5 Homeostasis
2. Describe and give examples for each 5. Name the organs located in each of
level of organization of the body. the body cavities. 9. Describe how a feedback system
maintains homeostasis.
6. Name the membranes that line each
1.2 Anatomical Terms body cavity, and the membranes that 10. Describe the role of each body
cover the organs. system in the maintenance of
3. Use anatomical terms to describe homeostasis.
the relative positions of the body
parts, the regions of the body, and 1.4 Organ Systems
the planes that can be used to 7. List the organ systems of the body, Medical Focus
section the body. and state the major organs Meningitis and Serositis
associated with each. Imaging the Body
atom
organ system
molecule
macromolecule
G
T
organ
C
A
G
A
organism
organelle
tissue
cell
Figure 1.1 Levels of organization of the human body. Each level is more complex than the previous level.
anterior
(ventral)
posterior
(dorsal)
ipsilateral contralateral
Figure 1.2 Directional terms. Directional terms tell us where body parts are located with reference to the body in
anatomical position.
cephalic (head)
ophthalmic (eye) cranial
frontal (forehead) (surrounding the brain)
orbital (eye cavity) occipital (back of head)
nasal (nose) auricular, otic (ear)
buccal (cheek)
oral (mouth)
cervical (neck) mental (chin)
acromial,
deltoid (shoulder) sternal (sternum) deltoid
pectoral (chest) thoracic (shoulder)
axillary (armpit) mammary (breast)
vertebral brachial (arm)
brachial (arm) (spinal
column)
antecubital
(front of elbow) abdominal (abdomen) cubital,
olecranal abdominal
umbilical (navel)
antebrachial (elbow) lumbar
(forearm) pelvic (lower back)
sacral
coxal (hip) inguinal (groin) antebrachial
carpal (wrist) gluteal
pubic, genital (buttock)
palmar (palm) (reproductive organs) dorsum
of the manus
hand (hand)
digital (finger)
tarsal (ankle)
pes, pedal (foot) dorsum of the foot
calcaneal (heel)
digital (toe) plantar (sole of foot)
a. Anterior view b. Posterior view
Figure 1.3 Terms for body parts and areas. (a) Anterior. (b) Posterior.
Median Parasagittal
(midsagittal) plane
plane
Transverse
a. A section along the (horizontal)
median plane plane
Frontal
b. A section along a frontal (coronal)
plane plane
Figure 1.4 Body planes and sections. Observation of internal parts requires sectioning the body along various planes.
cranial
cavity:
contains brain
posterior
(dorsal) body
vertebral
cavity
canal:
contains
thoracic spinal cord
cavity:
contains heart,
lungs, and
diaphragm
esophagus
spinal cord
abdominal
cavity:
anterior contains stomach,
(ventral) liver, spleen,
body pancreas,
cavity gallbladder,
abdominopelvic and intestines
cavity
pelvic
cavity:
contains
reproductive
and other
organs
a.
parietal
pleura
pleural cavity
pericardial cavity thoracic cavity:
parietal contains esophagus,
pericardium mediastinum heart, and lungs
abdominal cavity:
parietal contains digestive
peritoneum and other organs
abdominopelvic
cavity
pelvic cavity:
contains
reproductive and
b. other organs
Figure 1.5 The two major body cavities and their subdivisions. (a) Left lateral view (b) Frontal view.
stomach
right left
iliac hypogastric iliac
region region region
urinary bladder
Figure 1.7 The abdominopelvic cavity. The abdominopelvic cavity can be subdivided into (a) nine regions or (b) four quadrants.
The anterior and posterior body cavities are enclosed areas that are Pleurisy is an inflammation of the pleurae—linings of the tho-
protected by bone, muscle, connective tissues, and skin. Inflammation of racic cavity that also cover the lungs. It is often caused by a cold virus,
the membranes lining these cavities is a fairly rare, but serious, illness. If although it can signal the presence of more serious infections or even
body defenses are overcome by bacteria, viruses, or other microbes, the lung cancer. Its symptoms include chest pain that worsens with deep
result is a serious, potentially fatal infection and inflammation of the breathing, and pleural friction rub—a rough, grating sound in the chest
meninges (meningitis) or the serous membranes (serositis). Pleurisy, that can be heard with a stethoscope placed over the painful area. Treat-
pericarditis, and peritonitis are all forms of serositis. ment for pleurisy depends on its cause; most often, pleurisy that results
Meningitis is the term for inflammation of the meninges— from a common cold requires only pain medication such as aspirin or
linings of the posterior body cavity that cover the brain and spinal ibuprofen. Treatment for bacterial infection requires antibiotics.
cord. The most dangerous form is caused by bacteria that commonly Pericarditis affects the linings surrounding the heart. Like menin-
inhabit the nose. In the bacterial meningitis patient, a previous viral gitis, it often results from previous infections and can be extremely dan-
infection (which may be a simple common cold) allows these bacteria gerous. It is a common complication in drug abusers who use dirty needles
to enter the bloodstream and infect the meninges. Symptoms of bacte- for injections. Symptoms include severe chest pain (which may be mis-
rial meningitis include a severe headache and stiff neck, sensitivity to taken for a heart attack), fever, and weakness. Physicians can hear pericar-
light, fever, weakness, and fatigue. Even with aggressive antibiotic dial friction rub by placing a stethoscope over the patient’s heart. Fluid
treatment, bacterial meningitis is fatal in 25% of adults. The best treat- accumulation inside the pericardial sac surrounding the heart may inter-
ment is prevention by immunization—especially important for young fere with blood flow to and from the heart. Bacterial pericarditis is treated
college students living in the close quarters of a college dorm. with antibiotics, pain medications, and drugs that reduce swelling.
Peritonitis affects the lining of the abdominopelvic cavity. It
usually results from bacterial infection; a common cause of infection
is a ruptured appendix from appendicitis. Severe pain, fever, elevated
white blood cell counts, and tenderness are common symptoms.
site for possible Aggressive treatment with antibiotics is necessary to prevent bacteria
meningitis from invading the blood.
pelvic cavity
Figure 1A Meningitis and serositis. (a) Meningitis is infection or inflammation of the linings of the cranial cavity and vertebral
canal. (b) Serositis is infection or inflammation of the ventral body cavities. Pleurisy affects the pleural cavities, pericarditis affects
the pericardial cavity, and peritonitis affects the abdominopelvic cavities.
The internal environment of the body is the blood within the blood
vessels and the tissue fluid that surrounds the cells. Five systems Homeostasis is the relative constancy of the body’s internal envi-
add substances to and/or remove substances from the blood and ronment. Because of homeostasis, even though external conditions
tissue fluid: the cardiovascular, lymphatic, respiratory, digestive, may change dramatically, internal conditions stay within a narrow
and urinary systems. range. For example, regardless of how cold or hot one’s environ-
The cardiovascular system, discussed in Chapters 11 and 12, ment gets, the temperature of the body stays around 37°C (97° to
consists of the heart and the blood vessels that carry blood through 99°F). Likewise, no matter how acidic your meal, the blood’s acid-
the body. Blood transports nutrients and oxygen to the cells and ity remains relatively constant, and even if you eat a candy bar, the
removes waste molecules to be excreted from the body. Blood also amount of sugar in your blood is just about 0.1%.
contains cells produced by the lymphatic system, discussed in It is important to realize that internal conditions are not abso-
Chapter 13. The lymphatic system protects the body from disease. lutely constant; they tend to fluctuate above and below a particular
The respiratory system, discussed in Chapter 14, consists value. Therefore, the internal state of the body is often described
of the lungs and the tubes that take air to and from the lungs. The as one of dynamic equilibrium. If internal conditions change to any
respiratory system brings oxygen into the lungs and takes carbon great degree, illness results. This makes the study of homeostatic
dioxide out of the lungs. mechanisms medically important.
50
80
in room temperature activates the thermostat, which starts up the sends data to directs furnace
0 80
furnace. The heat given off by the furnace raises the temperature
5
60 70
thermostat to turn off
of the room to 68°F. Once the room is warmed, the furnace turns 688F set point
70°F
80
because warmth inactivates the system. 5 furnace off
0 80
too hot
5
60 70
too m
uch
Sensor Effect Homeostasis
too litt
le
negative feedback
and return to
negative feedback normal temperature
and return to normal stimulus
stimulus
too m Sensor
uch furnace on 60 70
0
Homeostasis 66°F
80
5
60 70
a.
Control center
Figure 1.8 Negative feedback. In both examples, an internal directs furnace 60 70
or external stimulus (pink) activates a sensor (green). In turn, the to turn on 0
80
5
sends data to
sensor signals a control center (tan) which causes an effect (blue). 50
60 80
thermostat
70
The effect reverses the starting stimulus, and the system returns
688F set point
to homeostasis. (a) The general pattern. (b) A mechanical example. b.
1 Head of fetus
pushes against
cervix
3 Brain stimulates
pituitary gland to
secrete oxytocin
Figure 1.10 Positive feedback. Positive feedback loops help the body to complete a process with a definite cutoff point, like labor
and delivery.
direction of
blood flow
Lymphatic System—Transportation and defense. The lymphatic
system assists the cardiovascular system. Lymphatic capillar-
ies collect excess tissue fluid, which is returned via lymphatic
vessels to the cardiovascular veins. Lymph nodes help to
purify lymph and keep it free of pathogens (disease-causing
agents such as bacteria and viruses). This action is assisted by
the white blood cells that are housed within lymph nodes.
Respiratory System—Gas exchange. The respiratory system
adds oxygen to and removes carbon dioxide from the blood.
It also plays a role in regulating acid-base balance in blood
and tissue fluid. Removal of CO2 helps to prevent excessive
acidity of the blood.
Digestive System—Nourishment and waste removal. The digestive
system takes in and digests food, providing nutrient molecules
to replace the nutrients that are constantly being used by the
arteriole tissue oxygen and carbon dioxide venule
cells nutrients and wastes
body cells. Substances that cannot be digested are eliminated.
The liver, an accessory digestive organ, also manufactures urea,
blood capillary a waste product of protein digestion. The liver also removes
Figure 1.11 Regulation of tissue fluid composition. Cells are toxic chemicals such as alcohol and other drugs. Additionally,
surrounded by tissue fluid (blue), which is continually refreshed the liver regulates blood glucose (sugar). As glucose enters the
because oxygen and nutrient molecules constantly exit the blood after a meal, any excess is removed by the liver and
bloodstream, and carbon dioxide and waste molecules continu- stored as glycogen. Later, the glycogen can be broken down to
ally enter the bloodstream. replace the glucose used by the body cells. In this way, the
glucose composition of blood remains constant.
Urinary System—Waste removal. Urea and other metabolic
Endocrine System—Control. Endocrine glands secrete
waste molecules are excreted by the kidneys, which are a
hormones into the blood. Endocrine hormones bring about
part of the urinary system. Urine formation by the kidneys is
a slower, more lasting change that keeps the internal
extremely critical to the body, not only because it rids the
environment relatively stable.
body of unwanted substances but also because urine forma-
Blood and Cardiovascular System—Transportation and defense.
tion offers an opportunity to carefully regulate blood volume,
Red blood cells and blood plasma (the liquid fraction of blood)
salt balance, and acid-base balance.
transport oxygen, carbon dioxide, nutrients, and wastes.
Reproductive System—Survival of the species. Although
Platelets in blood participate in the clotting process, preventing
individuals can survive and thrive without reproducing, the
excess blood loss. White blood cells defend against infection.
human species cannot continue without this vital system.
The cardiovascular system conducts blood to and away from
capillaries, where exchange occurs. The heart pumps the blood The contributions of each of the body’s systems are summarized
and thereby keeps it moving toward the capillaries. in the Human Systems Work Together illustration on pages 14 and 15.
Imaging the body for diagnosis of disease has certainly changed since
the accidental invention of the X ray by Wilhelm Roentgen in 1895.
Many new techniques allow clinicians to visualize internal structures
with great accuracy. The most widely used imaging technique remains
the X ray, which is produced when high-speed electrons strike a heavy
metal. Dense structures (such as bone) absorb X rays well, showing up
as light areas. Soft tissues absorb to a lesser extent and show up as dark
areas. Injecting opaque dye into blood vessels allows blood vessel visu-
alization, as in a coronary angiogram (an X ray of the heart’s arteries).
Digestive tract imaging is possible on patients who have first consumed
opaque dye solutions. In the past, X-ray images had to be developed on
photographic film for study. Now images can be digitized and projected
on a computer, making it possible to easily store and share an X ray.
A bone density scan is a specialized X ray. The patient is first
injected with a harmless radioactive tracer, which is rapidly taken up a. CT scan b. MRI
by bone. Subsequent X rays can reveal areas of increased bone metab-
olism (as in a cancerous tumor) or decreased metabolism (as in osteo-
porosis). Similarly, radioactive iodine is used to study the thyroid
gland because the thyroid is the only tissue to use the element iodine.
During computed tomography, or CT scan, a computer uses the
X ray information taken from various angles to form a series of cross
sections. CT scanning has reduced the need for exploratory surgery
and can guide the surgeon in visualizing complex body structures dur-
ing surgical procedures.
PET (positron emission tomography) and SPECT (single-photon
emission computerized tomography) are both variations on CT scan-
ning. Radioactively labeled compounds are injected into the body,
where they are taken up by metabolically active tissues. The tissues
then emit gamma rays. Again, a computer generates cross-sectional
c. fMRI d. PET scan
images of the body, but this time the image indicates metabolic activity
in addition to structure. PET scanning is used to diagnose brain disor- Figure 1B Techniques for imaging the body. (a) a CT scan
ders, such as a brain tumor, Alzheimer disease, epilepsy, or stroke. highlights bony structures in white, while soft tissue is dark.
During MRI (magnetic resonance imaging), the patient lies in a A contrast medium has to be used to see brain tissue. (b) In
an MRI, dense bone is dark and soft tissues are illuminated
massive, hollow, cylindrical magnet and is exposed to short bursts of
in lighter shades. (c) and (d) Both fMRI and PET scan show
a powerful magnetic field. This causes the protons in the nuclei of the
areas of highest metabolic activity.
body’s billions of hydrogen atoms to align. Then, when exposed to
strong radio waves, the protons move out of alignment and produce active brain tissue, which has a greater blood supply than neighboring
signals. A computer changes these signals into an image. Tissues with inactive regions. The newest MRI technology application, called diffu-
many hydrogen atoms (such as fat) show up as bright areas, while tis- sion tensor imaging, traces water movement in brain cells. Abnormal
sues with few hydrogen atoms (bone, for example) appear black. This cells have different water movement patterns than normal cells. Both
is the opposite of an X ray, which is why MRI is more useful than an imaging techniques are used to diagnose and treat brain injury and dis-
X ray for imaging soft tissues. However, many people cannot undergo ease (such as brain damage following a stroke, or Alzheimer disease),
MRI, because the magnetic field can actually pull a metal object (like and can also help to track cancer tumor growth and plan brain surgeries.
a tooth filling or an artificial hip) out of the body! The least expensive method of creating tissue images is sonogra-
MRI technology continues to evolve, enabling scientists to study phy, or ultrasound. High-frequency sound waves are transmitted into
the active brain. In functional magnetic resonance imaging (fMRI), as tissues, which reflect the sound waves to create an image. Sonography
with traditional MRI, the patient is placed inside a magnetic field. He or avoids both radiation exposure and rare allergic reactions to dyes. Ultra-
she is then asked to do small tasks (for example, touching thumb to fin- sound is safe for imaging the fetus in a pregnant woman, and can show
gers, or answering simple questions). fMRI highlights metabolically an amazing amount of detail, as you can see in the chapter introduction.
Summary
1.1 The Human Body function of these parts. Structure molecules, macromolecules, or-
A. Anatomy is the study of the is suited to the function of a part. ganelles, cells, tissues, organs,
structure of body parts, and The body has levels of organiza- organ systems, and finally, the
physiology is the study of the tion that progress from atoms to organism.
Study Questions
1. Distinguish between the study of State at least two anatomical terms 9. Name the major organ systems, and
anatomy and the study of that pertain to the head, thorax, describe the general functions of each.
physiology. (p. 2) abdomen, and limbs. (pp. 4–5) (pp. 8, 10)
2. Give an example that shows the rela- 6. Distinguish between a midsagittal 10. List the major organs found within
tionship between the structure and the section, a parasagittal section, a each organ system. (pp. 8, 10)
function of body parts. (p. 2) transverse section, and a coronal 11. Define homeostasis, and give exam-
3. List the levels of organization within section. (p. 5) ples of negative feedback and positive
the human body in reference to a 7. Distinguish between the posterior and feedback mechanisms. (pp. 10–13)
specific organ. (p. 2) anterior body cavities, and name two 12. Discuss the contribution of each body
4. What purpose is served by directional smaller cavities that occur within each. system to homeostasis. (pp. 12–15)
terms as long as the body is in anatom- (pp. 6–7) 13. Define the term disease. Compare
ical position? (pp. 3–4) 8. Name the four quadrants and the nine and contrast local vs. systemic
5. Distinguish between the axial and regions of the abdominopelvic cavity. disease, and acute vs. chronic
appendicular portions of the body. (p. 8) disease. (p. 17)
Learning Outcomes After you have studied this chapter, you should be able to:
20
Atoms
Matter is anything that takes up space and has mass. It can be a
solid, a liquid, or a gas. Therefore, we humans are matter, just like An atom is the smallest unit of an element that still retains the
the water we drink and the air we breathe. chemical and physical properties of the element. Although it is
possible to split an atom by physical means, an atom is the smallest
unit to enter into chemical reactions. For our purposes, it’s satisfac-
Elements and Atoms tory to think of each atom as having a central nucleus and pathways
All matter is composed of basic substances called elements. It’s about the nucleus called shells (sometimes called energy levels).
quite remarkable that there are only 92 naturally occurring elements. The subatomic particles called protons and neutrons are located
It is even more surprising that over 90% of the human body is com- in the nucleus, and electrons orbit about the nucleus in the shells
posed of just four elements: carbon, nitrogen, oxygen, and hydrogen. (Fig. 2.1b). Most of an atom is empty space. If we could draw an
Every element has a name and a symbol consisting of one or atom the size of a football stadium, the nucleus would be like a
two letters. For example, carbon has been assigned the atomic sym- gumball in the center of the field, and the electrons would be tiny
bol C (Fig. 2.1a). When the symbol consists of two letters, only the specks whirling about in the upper stands.
The atomic number of an atom tells you how many pro-
tons an atom has. All atoms of any particular element have the
Common Elements in Living Things
same number of protons. Protons carry a positive (1) charge, and
electrons have a negative (2) charge. Neutrons have no charge.
Atomic Atomic Mass Atoms are electrically neutral because the numbers of protons
Element Symbol Number Number Comment
and electrons are equal. For example, the atomic number of car-
hydrogen H 1 1 These bon is 6. Therefore, carbon has six protons and six electrons.
carbon C 6 12 elements How many electrons are in each shell of an atom? The inner shell
nitrogen N 7 14 make up
oxygen O 8 16 most is the lowest energy level and can hold only two electrons; after
phosphorus P 15 31 biological that, each shell, for the atoms noted in Figure 2.1a, can hold up
sulfur S 16 32 molecules. to eight electrons. Using this information, we can calculate that
sodium Na 11 23 These carbon has two shells and that the outer shell has four electrons.
magnesium Mg 12 24 elements The number of electrons in the outer shell determines the
chlorine Cl 17 35 occur mainly
potassium K 19 39 as dissolved
chemical properties of an atom, including how readily it enters
calcium Ca 20 40 salts. into chemical reactions. As we will see, an atom is most stable
a.
when the outer shell has eight electrons. (Hydrogen and helium,
p = protons with only one shell, are exceptions to this statement. Atoms with
n = neutrons only one shell are stable when this shell contains two electrons.)
= electrons If an atom gains or loses one or more electrons, it becomes an ion.
= nucleus An atom that acquires electrons becomes negatively charged, while
6p
an atom that loses electrons becomes positively charged.
6n The mass number of an atom is generally equal to the sum of its
protons and neutrons. Both protons and neutrons are so light that their
weight is indicated by a special designation called an atomic mass unit
(amu). An atom’s protons and neutrons each weigh one atomic mass
unit, and its electrons have almost no mass. Using this knowledge, you
can determine the number of neutrons in the nucleus of an atom. For
Carbon
example, here is how you calculate the number of neutrons in carbon
mass number
12 (C): Carbon’s mass number is 12, and you know from its atomic num-
6C ber that it has six protons. Thus, its mass number (12) minus its pro-
b. atomic number
tons (6) equals its neutrons (6). Likewise, the mass number of sodium
Figure 2.1 Elements and atoms. (a) The atomic sym- (23) minus its protons (11) equals its neutrons (12). (Fig. 2.1b)
bol, number, and mass number are given for common elements Further, as shown in Figure 2.1b, the atomic number of an
in the body. (b) The structure of carbon shows that an atom atom is often written as a subscript to the lower left of the atomic
contains the subatomic particles called protons (p) and neutrons
symbol. The mass number is often written as a superscript to the
(n) in the nucleus (colored pink) and electrons (colored blue) in
upper left of the atomic symbol. Thus, determining neutron number
shells about the nucleus.
is as easy as subtracting the bottom number from the top number.
1 2 Na1 Cl2
Na Cl
Figure 2.2 Ionic reaction. (a) During the formation of sodium chloride, an electron is transferred from the sodium atom to
the chlorine atom. At the completion of the reaction, each ion formed has eight electrons in the outer shell, but each also carries a
charge as shown. (b) In a sodium chloride crystal, bonding between ions creates a three-dimensional lattice in which each Na1 ion is
surrounded by six Cl2 ions, and each Cl2 is surrounded by six Na1.
that the atoms are sharing electrons. Just as two people’s hands
participate in a handshake, each atom contributes one electron to
the pair that is shared. These electrons spend part of their time in H
the outer shell of each atom; therefore, they are counted as belong-
ing to both bonded atoms. O + O
Covalent bonds can be represented in a number of ways. In con-
H
trast to the diagrams in Figure 2.3, structural formulas use straight lines H H
to show the covalent bonds between the atoms. Each line represents a
pair of shared electrons. A molecular formula describes the molecule’s oxygen 2 hydrogen water
composition, but molecular formulas indicate only the number of each O
type of atom making up a molecule. A comparison follows: H H
Properties of Water
Content CHECK-UP!
Polarity and hydrogen bonding cause water to have many proper-
1. One particular isotope of the element potassium has the following ties beneficial to life, including the three to be mentioned here.
symbol: 39K. The atomic number (number of protons) for potas-
sium is 19. How many neutrons are contained in this isotope? 1. Water is a solvent for polar (charged) molecules and ionic
compounds, and thereby facilitates chemical reactions both
2. Fluorine gas contains two atoms of fluorine that share two elec-
trons. Draw the structural and molecular formulas for fluorine gas. outside and within our bodies.
Answers in Appendix A. When ions and molecules disperse in water, they move about
and collide, allowing reactions to occur. Therefore, water is a
The world can be a pretty dangerous place for a child. Toddlers will ex- these cases, rapid transport to the emergency room can mean the differ-
amine a new object visually at first, and then it usually goes right into ence between life and death.
their mouths, often regardless of how awful the taste or smell might be. Whenever possible, the patient’s history should be recorded to give
Small children also mimic the older people in their lives, watching as clues about the ingested substance. The victim’s caregivers, relatives,
adults consume drinks or medication. Sometimes, curiosity leads to in- friends, and co-workers can help. Partially empty containers, spilled
discriminate tasting of substances such as lipstick, crayons, hand lotion, material, and evidence of recreational drug use such as needles and sy-
shaving cream, modeling clay, and chalk (all are not toxic in small doses, ringes provide valuable information about the poison’s possible identity.
but ingesting any of them still warrants a call to a poison control center). Once the poison is identified, local and national poison control centers
Unfortunately, accidental poisoning in children happens all too fre- can help, suggesting antidotes and therapies.*
quently when toxins are accessible. EMS personnel shouldn’t attempt to cause vomiting (unless a
Accidental poisoning occurs in adults as well, especially to seniors physician orders an emetic, a drug that causes vomiting). In the emer-
who may be confused about prescription medications. Obviously, poi- gency room, clinicians often have the patient drink a solution of
soning is intentional when an older child, teen, or adult attempts suicide. ground-up charcoal, called activated charcoal, which combines with
When date rape or murder is the motive, poisoning is also deliberate (see many different types of chemicals. Stomach pumping—repeated fill-
Focus on Forensics: Rape in Chapter 17 for further discussion of ing and emptying of the stomach to wash out the poison, with or with-
date rape). out charcoal solution—may also be used. However, if the poison is a
First responders must quickly take action: first, call 911. Then, chemical like gasoline or kerosene, or a burning chemical like drain
continue with the A-B-Cs of emergency care: A → establish an Airway cleaner, these procedures can’t be used because they might further
and make sure the person is Breathing, and maintain Circulation. (The damage the nose, throat, and esophagus. In very serious poisonings,
techniques of cardiopulmonary resuscitation are described in the patient may need dialysis, a technique for cleansing blood
Chapter 12). Other effects of the poison demand a quick reaction as well. artificially.
Alkaloid poisons like nicotine often increase pulse rate and blood
pressure to dangerous levels, while other toxins will cause the opposite *The U.S. National Poison Control Center Hotline telephone number is
effect. Further, many poisons cause delirium, seizures, and coma. In 1-800-222-1222.
awater
pure water, tears
egg wh an blood,
root
nor
ites, se
bre
ids
an a,
mal
beer
ad
ch od
tac
,b
hum
ma g s
rain
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lac
sto bakin
milk
e,
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kc
L ak sia
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alt gne
er
to
t S ma
ee
m
a
at
be s e f
er, oda Gr ilk o
oe
s
vin , m
eg nia
ar
mmo
ld a
6 7 8 ho
lem
5 9 use
on j
uice ho
4 10
Neutral pH
3 11
stomach
acid
2 12 oven
cleaner
1 13
H+ OH- sodium
0 14
hydrochloric Acidic Basic hydroxide
acid (NaOH)
Figure 2.5 The pH scale. The proportionate amount of hydrogen ions to hydroxide ions is indicated by the numerical values on the
dial. Any solution with a pH above 7 is basic, while any solution with a pH below 7 is acidic.
Note that the arrows shown in this chemical equation go forward dehydration H2O
and backward. This indicates that the reaction is reversible. When reaction
hydrogen ions are added to blood (let’s say, because you drink a can
of pop) the following reaction occurs:
a.
What happens if a person takes magnesium hydroxide (often
called milk of magnesia) for an upset stomach? When hydroxide
ions (OH−) are added to blood, this reaction occurs: subunit OH H subunit
Electrolytes
As we have seen, salts, acids, and bases are molecules that disso- subunit subunit
ciate; that is, they ionize in water. For example, when a salt such b.
as sodium chloride is put in water, the Na+ ion separates from the
Cl− ion. Figure 2.6 Synthesis and decomposition of
Substances that release ions when put into water are called macromolecules. (a) In cells, synthesis often occurs when
electrolytes because the ions can conduct an electrical current. The subunits bond following a dehydration reaction (removal of
H2O). (b) Decomposition occurs when the subunits in a
electrolyte balance in the blood and body tissues is important for
macromolecule separate after a hydrolysis reaction
good health because it affects the functioning of vital organs such
(addition of H2O).
as the brain and the heart.
H OH H OH H OH H OH H OH H OH H OH H OH
branched
nonbranched
glycogen
granule
starch
granule
cell wall
Figure 2.7 Starch structure and function. Starch has straight Figure 2.8 Glycogen structure and function. Glycogen is
chains of glucose molecules. Some chains are also branched, as more branched than starch. The electron micrograph shows
indicated. The electron micrograph shows starch granules in po- glycogen granules in liver cells. Glycogen is the storage form of
tato cells. Starch is the storage form of glucose in plants. glucose in humans.
linkage from that in starch or glycogen. Although this might seem 2.5 Lipids
to be a technicality, actually it is important because humans can-
10. Describe the composition of a neutral fat, and give examples of
not digest foods containing this type of linkage. Cellulose largely how lipids function in the body.
passes through our digestive tract as fiber, or roughage. Dietary
fiber is essential to good health, and its many functions will be
Lipids contain more energy per gram than carbohydrates and pro-
discussed in Chapter 15.
teins, and some function as long-term energy storage molecules
in organisms. Other lipids are part of cell membranes that enclose
individual cells, as well as membranes that surround the organelles
found inside cells. Steroids are a large class of lipids that includes,
Content CHECK-UP! among other molecules, the sex hormones.
7. Categorize each carbohydrate as a monosaccharide, Lipids are diverse in structure and function, but they have a
disaccharide, or polysaccharide: common characteristic: They do not dissolve in water. Their low
a. glucose solubility in water is due to an absence of polar groups. They con-
tain little oxygen and consist mostly of carbon and hydrogen atoms.
b. fructose
c. sucrose
Fats and Oils
d. starch
The most familiar lipids are those found in fats and oils. Fats, which
e. glycogen
are usually of animal origin (e.g., lard and butter), are solid at room
f. cellulose
temperature. Oils, which are usually of plant origin (e.g., corn oil
8. The carbohydrate that humans eat, but cannot digest, is and soybean oil), are liquid at room temperature. Fat has several
______. functions in the body: It is used for long-term energy storage, it
Answers in Appendix A. insulates against heat loss, and it forms a protective cushion around
major organs.
H H H H H H dehydration reaction O H H H H H H
O
1 C C C C C C C H H C O C C C C C C C H
H C OH HO hydrolysis reaction
1 3 H2O
H H H H H H H H H H H H
H H H H H O H H H H H
O
C C C C C C H H C O C C C C C C H
H C OH HO
H H H H H H H
H
Figure 2.9 Synthesis and degradation of a fat molecule. Fatty acids can be saturated (no double bonds between carbon atoms) or
unsaturated (have double bonds, colored yellow, between carbon atoms). When a fat molecule forms, three fatty acids combine with
glycerol, and three water molecules are produced.
A fat or an oil forms when one glycerol molecule reacts with Fatty acids are either saturated or unsaturated. Saturated fatty
three fatty acid molecules (Fig. 2.9). Fats and oils are sometimes acids have only single covalent bonds because the carbon chain
called triglycerides because of their three-part structure. They can is saturated, or combined with all the hydrogens it can hold. Fats
also be referred to as neutral fats because the molecules are non- such as lard, bacon grease, and butter are solid at room temperature
polar and have no electrical charge. because they contain saturated fatty acids. Unsaturated fatty acids
have double bonds between carbon atoms wherever fewer than two
Emulsification hydrogens are bonded to a carbon atom. Oils such as safflower,
corn, and peanut oil are liquid at room temperature because of their
Emulsifiers can cause fats to mix with water. They contain
unsaturated fatty acids. Hydrogenation of vegetable oils can convert
molecules with a nonpolar end and a polar end. The molecules
them to margarine and products such as Crisco®. For more about
position themselves about an oil droplet so that their nonpolar
the role of fats and oils in nutrition, health, and wellness, check out
ends project. Now the droplet disperses in water, which means that
Chapter 15.
emulsification has occurred.
Phospholipids
Phospholipids, as their name implies, contain a phosphate group
polar (Fig. 2.10a). Essentially, they are constructed like fats, except that
end in place of the third fatty acid, there is a phosphate group or a
+
nonpolar grouping that contains both phosphate and nitrogen. Unlike fats and
end oils, phospholipid molecules are not electrically neutral because
emulsifier fat the phosphate and nitrogen-containing groups are ionized. They
form the so-called hydrophilic head of the molecule, while the rest
emulsion of the molecule becomes the hydrophobic tails. Because of their
unique chemistry, phospholipids form the backbone of cellular
Soaps and detergents are emulsifiers that can remove fats and membranes. When surrounded by water (as body cells are), their
oils from dirty clothes or dishes. In our bodies, fats and oils from hydrophilic phosphate heads face outward while the hydrophobic
food must be emulsified before they can be digested. Bile is the fatty acid tails are sandwiched in between. Thus, phospholipids
emulsifier produced by the liver, stored in the gallbladder, and re- spontaneously create a double layer, called a bilayer (Fig. 2.10b).
leased when you eat a fat-containing meal.
Steroids
Saturated and Unsaturated Fatty Acids Steroids are lipids that have an entirely different structure from that
A fatty acid is a carbon–hydrogen chain that ends with the acidic of fats. Steroid molecules have a backbone of four fused carbon
group —COOH (Fig. 2.9). Most of the fatty acids in cells contain rings, called the steroid nucleus. Each one differs primarily by
16 or 18 carbon atoms per molecule, although smaller ones with the side-chain molecules, called functional groups, attached to
fewer carbons are also known. the rings.
b. Primary Structure:
sequence of amino acids
H3N+
amino acid
COO–
peptide bond
c. Secondary Structure:
alpha helix or a pleated sheet C
hydrogen bond
O C C
O C
CH N N C
C R H O H O
O N C C C
CH R
C H R C N
N C O H
CH R O H R
H N C
H N
R C
O N C C O
C R O
CH O H N
C H C C R
N R
CH O N N C
H R H O H O R
N R C C C
O C
H R C N
hydrogen bond O C
CH C O H R H
N H N C
CH R N
C C
N R C O
O H
CH N
b (beta) sheet =
a (alpha) helix
pleated sheet
d. Tertiary Structure:
final shape of polypeptide disulfide bond
e. Quaternary Structure:
two or more associated
polypeptides
Figure 2.12 Levels of polypeptide structure. (a) Amino acids are the subunits of polypeptides. Note that an amino acid con-
tains nitrogen. (b) Polypeptides differ by the sequence of their amino acids, which are joined by peptide bonds. (c) A polypeptide often
twists to form a coil or folds into a sheet due to hydrogen bonding between amino acids in the primary sequence. (d) The tertiary struc-
ture of polypeptide structure is due to various types of bonding between the R groups of the amino acids. (e) The grouping of two or
more polypeptides creates the quaternary structure of a large protein molecule.
Infectious diseases are known to be caused by minute organisms that ultimately starve. Sheep with scrapie will frantically rub wool off
successfully dodge the body’s defense mechanisms. These invaders their bodies. Infected humans lose memory, muscle control, and
include parasites such as liver flukes and parasitic worms; smaller, finally stop breathing. At this time, there is no treatment—all TSEs
one-celled parasites like disease-causing strains of Amoeba; and the are fatal.
smallest unicellular organisms, the bacteria. Viruses are disease- The addition of waste brain/spinal cord tissue from slaughter-
causing particles that are even smaller than bacteria. All of these dis- houses to animal feed has been outlawed in all TSE-affected coun-
ease agents share a common trait: All contain the nucleic acids DNA tries, because researchers believe that prions were initially spread
or RNA, or both. Nucleic acids are large molecules that comprise the from sheep to cattle, and later among infected cattle, when the ani-
genetic material of parasites, bacteria, and viruses. At one time, mals ate contaminated feed. (It is interesting to note that kuru in
scientists believed that infectious organisms had to contain genetic humans was spread by cannibalism among the Fore’ tribe of New
material. Guinea, who honored dead relatives by eating their brains!) Further,
However, disease outbreaks in England, Europe, Canada, and the hunters are now being warned to protect against chronic wasting dis-
United States have demonstrated that even smaller agents, consisting ease by discarding meat from deer or elk that appear ill, to strictly
only of a protein molecule, are capable of causing disease. These pro- avoid contact with any brain or spinal cord tissue (especially con-
teinaceous infectious particles, called prions (pronounced pree- sumption of the tissue!) and to wear gloves if a carcass is butchered in
ahns), are responsible for a set of diseases termed transmissible the field.
spongiform encephalopathies (TSEs). There are numerous forms of However, human-to-human TSE transmission can occur if cer-
TSEs: Creutzfeld-Jakob (croits-feld yay-kob) disease and kuru in tain types of brain-derived matter, including brain coverings, corneas
humans, bovine spongiform encephalopathy (formerly termed “mad from the eyes, and certain hormones are transferred from an infected
cow disease”) in cattle, scrapie in sheep, and chronic wasting disease in donor into a recipient. Prion-contaminated neurosurgery instruments
wild deer and elk, among others. (In addition, some spongiform can also infect a patient.
encephalopathies are inherited.) All human and animal TSE victims To date, probable diagnosis of TSEs has relied on analysis of
show similar findings at autopsy: holes pockmark the brain, giving cerebrospinal fluid (fluid obtained from a spinal tap) and electroen-
the tissue a spongy, Swiss-cheese appearance. Currently, TSEs cephalogram, or EEG. Absolute confirmation of the disease could
affect approximately 1:1,000,000 in a given population each year. In only be determined at autopsy. Recently developed blood tests have
the U.S., this currently translates to 250 to 300 newly infected people successfully detected prion proteins in individuals with one form of
per year. Creutzfeld-Jakob disease. Perhaps early discovery could lead to an
Scientists theorize that prions cause normal brain cell proteins to effective treatment. Very early research has shown success in treating
change into prion proteins. Accumulating prions kill brain cells and prion disease in test tube cultures of nerve cells. However, many
spread throughout brain tissue. Symptoms indicate brain destruction: puzzling questions about prions remain, and much additional research
“Mad” cows (deer and elk as well) wobble, stagger, refuse food, and is needed.
Replacement (Exchange) Reactions Replacement reactions 14. What type of reaction is the digestion of glucose to form car-
involve both degradation (decomposition) and synthesis. Reactions bon dioxide and water?
between acids and bases are replacement reactions. For example, a. synthesis c. replacement
when hydrochloric acid (HCl) is reacted with sodium hydroxide b. degradation/decomposition
(NaOH), the chloride ion (Cl−) trades places with the hydroxide ion Answers in Appendix A.
(OH−). Table salt (NaCl) and water (H2O) are formed as a result.
Content CHECK-UP!
2.7 Nucleic Acids
12. The sequence of amino acids found in a protein is that pro-
12. Describe the structure and function of DNA and RNA
tein’s _______ structure. in cells.
a. primary c. tertiary 13. Explain the importance of ATP in the body.
b. secondary d. quaternary
13. What happens to a protein when it is denatured? How would Nucleic acids are huge macromolecules composed of nucleotides.
this affect biologically active proteins? Every nucleotide is a molecular complex of three types of subunit
enzyme enzyme
substrates substrate
enzyme–substrate enzyme–substrate
complex complex
enzyme enzyme
a. Synthesis b. Degradation/Decomposition
Substrates are combined A substrate is broken
to produce a larger product. down to smaller products.
Figure 2.13 Enzymatic action. An enzyme has an active site where the substrates come together and react. The products
are released, and the enzyme is free to act again. (a) In synthesis, the substrates join to produce a larger product. (b) In degradation/
decomposition, the substrate breaks down to smaller products.
molecules—a phosphate (phosphoric acid), a pentose sugar, and a have two rings (like adenine or guanine) or one ring (like thymine
nitrogen-containing base: or cytosine). In RNA, the base uracil replaces the base thymine.
The bases in DNA and RNA are nitrogen-containing bases—
nitrogen- that is, a nitrogen atom is a part of the ring. Like other bases, the
phosphate C containing
P
base
presence of the nitrogen-containing base in DNA and RNA raises
the pH of a solution.
5' O The nucleotides in DNA and RNA form a linear molecule
4' S called a strand. A strand has a backbone made up of phosphate-
1'
sugar-phosphate-sugar, with the bases projecting to one side of the
3' 2' backbone. Because the nucleotides occur in a definite order, so do
pentose sugar
the bases. Any particular DNA or RNA has a definite sequence of
Nucleic acids contain hereditary information that determines bases, although the sequence can vary between molecules. RNA
which proteins a cell will have. Two classes of nucleic acids are is usually single-stranded, while DNA is usually double-stranded,
in cells: DNA (deoxyribonucleic acid) and RNA (ribonucleic with the two strands twisted about each other in the form of a
acid). DNA makes up the hereditary units called genes. Genes double helix (like a spiral staircase). The molecular differences
pass on from generation to generation the instructions for rep- between DNA and RNA are listed in Table 2.1.
licating DNA, making RNA, and joining amino acids to form
the proteins of a cell. RNA is an intermediary in the process of
TABLE 2.1 DNA Structure Compared
protein synthesis, conveying information from DNA regarding
to RNA Structure
the amino acid sequence in proteins. As an analogy, think of
DNA as a “blueprint”—a set of instructions for assembling an DNA RNA
entire building. Using this example, RNA would be the direc-
tions, made from the blueprint, describing how to put beams Sugar Deoxyribose Ribose
together to make a wall.
Bases Adenine, guanine, thymine, Adenine, guanine,
The nucleotides in DNA contain the 5-carbon sugar deoxy- cytosine uracil, cytosine
ribose; the nucleotides in RNA contain the sugar ribose. This
difference accounts for their respective names. As indicated in Strands Double-stranded Single-stranded
Figure 2.14, there are four different types of bases in DNA: A 5 ad-
Helix Yes No
enine, T 5 thymine, G 5 guanine, and C 5 cytosine. The base can
P P
T
A
S
S
P P
C
G
S
S
C
G
A P P
T
T one A
nucleotide
C G S
S
T
A
P C P
G
S
S
P P
T
A
S
S
hydrogen bond
3' end 5' end
Figure 2.14 Overview of DNA structure. (a) Double helix. (b) Complementary base pairing between strands. (c) Ladder con-
figuration. Notice that the uprights are composed of phosphate and sugar molecules and that the rungs are complementary paired bases.
In DNA, the two strands are held together by hydrogen ATP (Adenosine Triphosphate)
bonds between the bases (Fig. 2.14). When unwound, DNA
Individual nucleotides can have metabolic functions in cells. Some
resembles a stepladder. The sides of the ladder are made entirely
nucleotides are important in energy transfer. When adenosine
of phosphate and sugar molecules, and the rungs of the lad-
(adenine plus ribose) is modified by the addition of three phos-
der are made only of complementary paired bases. Thymine (T)
phate groups, it becomes ATP (adenosine triphosphate), the pri-
always pairs with adenine (A), and guanine (G) always pairs with
mary energy carrier in cells.
cytosine (C) (Fig. 2.14). This is called complementary base
Cells require a constant supply of ATP. To obtain it, they
pairing.
continually break down glucose (and other food molecules as
Complementary bases pair because they have shapes that
well) and convert the energy that is released into ATP mol-
fit together. We’ll see that complementary base pairing allows
ecules. To give an analogy, the energy in glucose is like a $100
DNA to replicate in a way that ensures the sequence of bases will
bill, and the energy in ATP is like a $10 bill. The larger bill
remain the same. When RNA is produced, complementary base
(glucose energy), when broken down, will yield ten smaller bills
pairing occurs between DNA and RNA, but uracil takes the place
(ATP energy). Cells “spend” ATP energy when cellular reac-
of thymine. Then, the sequence of the bases in RNA determines
tions require energy. Therefore, ATP is called the energy cur-
the sequence of amino acids in a protein because every three bases
rency of cells.
code for a particular amino acid (see Chapter 3, pp. 56–58). The
However, converting food energy into ATP energy is not
code is nearly universal and is the same in other organisms as it is
100% complete. To continue the comparison, imagine that a store
in humans.
*energy available
for cell functions
energy
input*
P P + P
won’t accept your $100 bill because it’s too large. You go to a
bank and exchange your $100 bill for $10 bills. Naturally, you Content CHECK-UP!
receive ten $10 bills from the bank—but you lose six $10 bills on 15. For the following terms, indicate whether it is characteristic of
the way home. RNA, DNA, or both:
A similar situation occurs for body cells. Energy in foods must a. uracil
be released, but during the conversion about 60% of food energy is
b. single-stranded
not converted to ATP. In the body, this energy is given off as heat.
c. cytosine
Thus, energy released from the breakdown of food fuels cellular
reactions and warms the body at the same time. d. thymine
Cells use ATP energy when macromolecules such as carbohy- e. double-stranded
drates and proteins are synthesized. In muscle cells, ATP is used f. ribose
for muscle contraction. In nerve cells, it is used for the conduction 16. Suppose someone presented data from DNA analysis of a
of nerve signals. Likewise, all other body cells use ATP energy to newly discovered species showing that the relative amounts
fuel their various functions. of the DNA bases were 30% guanine, 20% thymine, 30% ad-
ATP is a high-energy molecule because the last two enine, and 20% cytosine. Based on what you know about DNA
phosphate bonds are unstable and easily broken. In cells, the structure, why doesn’t this data make sense?
terminal phosphate bond is usually hydrolyzed, releasing 17. The complimentary base sequence for TTAGC is __________.
energy for cell reactions. The terminal bond is sometimes called 18. The breakdown of ATP yields ________, a phosphate group,
a high-energy bond, symbolized by a wavy line. But this termi- and energy.
nology is misleading—the breakdown of ATP releases energy Answers in Appendix A.
because the products of hydrolysis are more stable than ATP.
Breakdown of ATP leaves one molecule of ADP (adenosine
diphosphate) and a molecule of inorganic phosphate,
(Fig. 2.15). Begin Thinking Clinically
After ATP breaks down and the energy is used for a cellu-
lar purpose, ATP is rebuilt by the addition of to ADP again The disease sickle-cell anemia results from improper substi-
(Fig. 2.15). There is enough energy in one glucose molecule tution of a single DNA base (in this case, in part of the DNA
to build roughly 36 to 40 ATP molecules in this way. Homeo- sequence that ultimately results in hemoglobin, blood’s oxy-
stasis is only possible because cells continually produce and use gen-carrying protein). If DNA’s structure is defective, what
ATP molecules. The use of ATP as the energy currency of cells are the other two types of molecules that will be affected?
also occurs in other organisms, ranging from bacteria to humans. Answer and discussion in Appendix A.
On August 6, 1945, and then again on August 9, 1945, the world However, high levels of environmental ionizing radiation can
saw the effects of massive doses of ionizing radiation as two be deadly. By reacting with molecules in the body, each damages
atomic bombs were dropped: first on Hiroshima, Japan, and subse- cells and tissues. Acute radiation poisoning occurs when a per-
quently on Nagasaki. Fast-forward to March 2011: a massive son’s entire body is exposed to 1 Gy or more, from radioactive
earthquake and subsequent tsunami in Japan damaged nuclear alpha or beta particles touching the skin, consumed in contami-
reactors in Fukushima, Japan, causing release of radioactive steam nated food or drink, or inhaled from the air. Because gamma rays
into the air. Three people were killed in this accident, and radioac- aren’t particles, they directly penetrate the body. Recent research
tive fallout will likely contaminate soil and water for centuries. has shown that radiation breaks down cell-to-cell connections in
Small-scale radiation accidents have also repeatedly happened in the small intestine, allowing bacteria to enter the bloodstream.
the decades following the discovery of radiation in the early The first signs of acute radiation poisoning are nausea, vomiting,
twentieth century. For example, there are many people who have and diarrhea, and the faster these symptoms appear, the greater
been exposed to high-level radiation by accidental contact with the dosage. Bone marrow that produces blood cells is destroyed,
radioactive waste. and the person becomes anemic (due to red blood cell death) and
What is ionizing radiation? As the name suggests, it’s an at risk for infection (due to white blood cell destruction). In the
extremely high-powered form of energy that causes ions—charged days or weeks following exposure, any tissue with a rapid growth
subatomic particles—to form when unstable radioactive chemical ele- rate—skin and digestive tract lining, for example—may be
ments fall apart. There are three forms of ionizing radiation: alpha destroyed. A dose of 6 Gy or greater is almost always fatal. Over
particles, beta particles, and gamma rays. Alpha particles consist of time, radiation exposure predisposes a person to many forms
two protons and two neutrons. When a radioactive element spits out of cancer.
an alpha particle, it actually changes into a new element. For example, Acute radiation poisoning caused by alpha or beta particles is
if radium (atomic number 88) releases its alpha particle, it changes treated by having the person consume very high doses of stable
into radon gas (atomic number 86) because it loses two protons. Beta forms of the radioactive element. For example, exposure to radio-
particles are formed when an excess neutron converts to a proton active iodine (following a nuclear reactor incident) is treated by
(which remains in the element) and an electron (which is given off as taking pills containing stable iodine compounds. However, once
a very high-speed particle). As with an alpha-particle emitter, a radio- radiation poisoning injury has occurred, the patient must receive
active element that gives off a beta particle becomes a new element— intensive supportive treatment if he or she is to live. Long-term
this time, by adding a proton. For example, radioactive strontium therapy using intravenous fluids, blood transfusions, antibiotics to
(atomic number 38) becomes yttrium (atomic number 39) by releas- fight infections, drugs to stimulate bone marrow growth, and pain
ing a beta particle. Gamma rays are pure energy. medication will all be essential to keep the person alive until dam-
Throughout our lives, we’re all exposed to many forms of low- aged organs or tissues can regrow.
level ionizing radiation: from cosmic and solar energy, radioactive There are practical ways to prevent radiation poisoning in our
material in soil and water, and radiation used for medical procedures day-to-day lives. In homes, screen for radon gas, which can be
such as dental X rays and mammograms. Absorbed radiation is mea- released from soil surrounding a basement. If you’re preparing to
sured in units called grays, abbreviated Gy. The typical person’s aver- receive an X ray, CT scan, or other medical procedure, ask to have
age annual dosage of radiation from all sources is 0.0062 Gy. As you other body areas shielded from ionizing radiation. Avoid contact
know, there are many medical and commercial uses for radioactive with radioactive waste. Contact the authorities if you discover radio-
elements. For example, radioactive material selectively destroys can- active material (for example, discarded medical or industrial waste).
cer tissue during radiation therapy, and gamma rays are used to steril- Most important, seek immediate medical attention if you’re acciden-
ize delicate surgical equipment. tally exposed.
Summary
2.1 Basic Chemistry and mass number (number of neutrons. Radioisotopes are
A. All matter is composed of ele- protons and neutrons). The used in medicine in a variety of
ments, each made up of just one isotopes of some atoms are ways, from imaging the body to
type of atom. An atom has an radioactive and have biological killing cancer cells.
atomic symbol, atomic number and medical applications. c. Atoms react with one another to
(number of protons and, there- B. Isotopes of the same element form molecules. Following an
fore, electrons when neutral), have a different number of ionic reaction, charged ions are
Study Questions
1. Name the subatomic particles of an 8. What are buffers, and how do they 14. Name two steroids that function as sex
atom. Using the carbon atom as an ex- function? (p. 28) hormones in humans. (p. 32)
ample, describe their charge, atomic 9. Name the four categories of 15. What are some functions of proteins?
mass unit, and location. (p. 22) macromolecules (polymers) in cells; Why do proteins stop functioning if
2. What is an isotope? A radioactive give an example for each category, exposed to the wrong pH or high
isotope? Discuss the clinical uses of and name the subunits (monomers) temperature? (pp. 32–33)
radioactive isotopes. (p. 23) of each. (pp. 28–29) 16. Discuss the levels of protein structure.
3. Give an example of an ionic reaction, 10. Tell how macromolecules are built up (pp. 33–34)
and explain it. (p. 23) and broken down. (p. 28) 17. How do enzymes function? Name
4. Give an example of a covalent 11. Name some monosaccharides, disac- three types of metabolic reactions.
reaction, and explain it. (pp. 23–25) charides, and polysaccharides, and give (pp. 33, 35)
5. Relate three characteristics of water the functions for each. (pp. 29–30) 18. Discuss the structure and function of
to its polarity and hydrogen bonding 12. What is a lipid? A saturated fatty acid? the nucleic acids DNA and RNA.
between water molecules. (pp. 25–26) An unsaturated fatty acid? What is the (pp. 36–37)
6. What is an acid? A base? (p. 26) function of fats? (pp. 30–31) 19. What is ATP? How does the cell use
7. On the pH scale, which numbers 13. Relate the structure of a phospholipid ATP as the energy source for cell reac-
indicate a basic solution? An acidic to that of a neutral fat. What is the tions? (pp. 37–39)
solution? Why? (pp. 26–28) function of a phospholipid? (p. 31)
Learning Outcomes After you have studied this chapter, you should be able to:
3.1 Cellular Organization 7. Describe the structures of centrioles, 12. As a part of interphase, also describe
cilia, and flagella and their roles in how cells carry out protein synthesis.
1. Name the three main parts of a cellular movement.
human cell. 13. Describe the phases of mitosis, and
8. Describe the structures and function explain the function of mitosis.
2. Describe the structure and function of the cytoskeleton.
of the plasma membrane.
3. Explain the structure and function of Visual Focus
3.2 Crossing the Plasma Membrane
the nucleus. The Cell
9. Describe how substances move
4. Describe the structures and roles of
across the plasma membrane, and
the endoplasmic reticulum and the
distinguish between passive and
Medical Focus
Golgi apparatus in the cytoplasm. Dehydration and Water Intoxication
active transport.
5. Detail the structures of lysosomes
and the role of these organelles in 3.3 The Cell Cycle Focus on Forensics
the breakdown of molecules.
10. Describe the phases of the cell cycle. DNA Fingerprinting
6. Describe the structure of
mitochondria and their role in 11. As a part of interphase, describe the
producing ATP. process of DNA replication.
42
MEMBRANOUS STRUCTURES
Plasma membrane Phospholipid bilayer with embedded proteins Cell border; selective passage of molecules into and
out of cell; location of cell markers, cell receptors
Nucleus Nuclear membrane (envelope) surrounding Storage of genetic information; control center of cell;
nucleoplasm, chromatin, and nucleolus cell replication
Nucleolus Concentrated area of chromatin, RNA, and Ribosomal formation
proteins; found in the nucleus
Ribosome Two subunits composed of protein and RNA Protein synthesis
Endoplasmic reticulum Complex system of tubules, vesicles, and sacs Synthesis and/or modification of proteins and other
substances; transport by vesicle formation
Rough endoplasmic reticulum Endoplasmic reticulum studded with ribosomes Protein synthesis for export
Smooth endoplasmic reticulum Endoplasmic reticulum without ribosomes Varies: lipid and/or steroid synthesis; calcium storage
Golgi apparatus Stacked, concentrically folded membranes Processing, packaging, and distribution of molecules
Vacuole Small membranous sac Isolates substances inside cell
Vesicle Small membranous sac Storage and transport of substances into/out of cell
Lysosome Vesicle containing digesting enzymes Intracellular digestion; self-destruction of the cell
Peroxisome Vesicle containing oxidative enzymes Detoxifies drugs, alcohol, etc.; breaks down fatty acids
Mitochondrion Inner membrane within outer membrane Cellular respiration
Cytoskeleton Microtubules, actin filaments Shape of cell and movement of its parts
Cilia and flagella 9 1 2 pattern of microtubules Movement by cell; movement of substances inside a tube
Centriole 9 1 0 pattern of microtubules Formation of basal bodies for cilia and flagella;
formation of spindle in cell division
plasma
membrane
nuclear
envelope
nucleolus
chromatin
endoplasmic
reticulum
PLASMA MEMBRANE:
outer surface that
regulates entrance and
exit of molecules
protein a. 50 nm
Figure 3.1 The Cell. (a) Transmission electron micrograph of the cell. (b) The interior of the cell, with its organelles.
carbohydrate
chain
hydrophobic hydrophilic
tails heads
phospholipid
bilayer
cholesterol
protein
Figure 3.2 Fluid-mosaic model of the plasma membrane. In the phospholipid bilayer, the hydrophilic (polar) heads are on
the inner and outer surfaces of the bilayer, and the hydrophobic (nonpolar) tails are sandwiched in between the two hydrophilic layers.
Embedded proteins are scattered throughout the bilayer. Carbohydrate molecules attach to lipids to form glycolipids. Likewise, carbohy-
drates and proteins form glycoproteins.
have particular pieces of furniture that serve a particular purpose, water, they naturally form a spherical bilayer because of the chemi-
organelles have a structure that suits their function. cal properties of the heads and the tails.
Cells also have a cytoskeleton, a network of interconnected At body temperature, the phospholipid bilayer is a liquid;
filaments and tiny hollow tubes called microtubules in the cyto- it has the consistency of olive oil, and the proteins are able to
plasm. The name cytoskeleton is convenient because it allows us change their positions by moving laterally. The fluid-mosaic
to compare the cytoskeleton to our bones and muscles. Bones and model, a working description of membrane structure, suggests
muscles give us structure and produce movement. Similarly, the that the protein molecules have a changing pattern (form a
elements of the cytoskeleton maintain cell shape and allow the mosaic2) within the fluid phospholipid bilayer (Fig. 3.2). Our
cell and its contents to move. Some cells move by using cilia and plasma membranes also contain a substantial number of cho-
flagella, which are made up of microtubules. lesterol molecules. These molecules stabilize the phospho-
lipid bilayer and prevent a drastic decrease in fluidity at low
The Plasma Membrane temperatures.
Short chains of sugars are attached to the outer surfaces of
Our cells are surrounded by an outer plasma membrane. The some proteins and lipids within the plasma membrane. This cre-
plasma membrane separates the cytoplasm and organelles inside ates molecules termed glycoproteins and glycolipids, respectively.
the cell from the outside of the cell. Plasma membrane integrity is Unique glycoprotein molecules, specific to each cell, mark the cell
necessary for the cell to live. as belonging to a particular individual. These cell markers account
The plasma membrane is a phospholipid bilayer with attached for characteristics such as blood type or why a patient’s system
(also called peripheral) or embedded (also called integral) pro- sometimes rejects an organ transplant. Some glycoproteins have
teins. As you discovered in Chapter 2, each phospholipid molecule a special configuration that allows them to act as receptors for
has a polar head and nonpolar tails (Fig. 3.2). Because the polar
heads are charged, they are hydrophilic (water-loving) and face
outward, where they are likely to encounter a watery environment.
2
A mosaic is a picture or decorative design that’s created when pieces of colored
The nonpolar tails are hydrophobic (water-fearing) and face in- glass, tile, or paper are placed in or on a surface to create a pattern. In the fluid-mosaic
ward, where there is no water. When phospholipids are placed in analogy, proteins are placed into the phospholipid layer.
nuclear
envelope
chromatin
nucleolus
rough ER
ribosome
smooth ER
Figure 3.4 Endoplasmic reticulum. Rough endoplasmic reticulum is studded with ribosomes where protein synthesis occurs.
Smooth endoplasmic reticulum, which has no attached ribosomes, produces lipids and often has other functions as well in particular cells.
secretion
1 plasma
membrane
secretory
vesicle
incoming vesicle
2
enzyme 2
Golgi apparatus
3 modifies lipids and proteins
lysosome
from the ER; sorts and packages
contains digestive enzymes
them in vesicles
that break down macromolecules
entering by vesicles
protein
transport vesicle
transport vesicle takes proteins to
1
takes lipids to Golgi apparatus
Golgi apparatus
lipid
rough endoplasmic
smooth endoplasmic reticulum
reticulum synthesizes proteins and
synthesizes lipids and has packages them in vesicles
various other functions Nucleus
ribosome
a. Endocytosis b. Exocytosis
Figure 3.5 The endomembrane system. (a) Endocytosis and lysosome function. (1) A vesicle formed by endocytosis,
containing macromolecules, fuses with (2) the lysosome made at the Golgi apparatus, and (3) lysosome enzymes digest the macro-
molecules in the vesicle. (b) Exocytosis and the secretory vesicle. (1) Transport vesicles from the ER bring proteins and lipids to the
Golgi apparatus, where (2) the molecules are packaged in a secretory vesicle, which (3) travels to the plasma membrane, releasing
its contents by exocytosis.
Mitochondria
Although the size and shape of mitochondria (sing., mitochondrion)
can vary, all are bounded by a double membrane. The inner mem-
brane is folded to form little shelves called cristae, which project
into the matrix, an inner space filled with a gel-like fluid (Fig. 3.6).
The matrix also contains mitochondrial DNA, which is distinct
from nuclear DNA.
Mitochondria are the site of ATP (adenosine triphosphate)
a.
production involving complex metabolic pathways. As described 200 nm
outer
in section 2.7, ATP molecules are the common carrier of energy in membrane matrix
cells. A shorthand way to indicate the chemical transformation that intermembrane inner cristae
involves mitochondria is as follows: space membrane
ADP + P ATP
b.
Mitochondria are often called the powerhouses of the cell: Just
as a powerhouse burns fuel to produce electricity, the mitochondria
Figure 3.6 Mitochondrion structure. Mitochondria
convert the chemical energy of carbohydrate molecules into the are involved in cellular respiration. (a) Electron micrograph of a
chemical energy of ATP molecules. In the process, mitochondria mitochondrion. (b) Generalized drawing in which the outer
use up oxygen and give off carbon dioxide and water. The oxygen membrane and portions of the inner membrane have been cut
you breathe in enters cells and then mitochondria; the carbon diox- away to reveal the cristae.
ide you breathe out is released by mitochondria. Because oxygen
is used up and carbon dioxide is released, we say that mitochondria
carry on cellular respiration. includes microtubules, intermediate filaments, and actin filaments
Fragments of digested carbohydrate, protein, and lipid enter (see Fig. 3.1).
the mitochondrial matrix from the cytoplasm. The matrix contains Microtubules are hollow cylinders whose wall is made up of
enzymes for metabolizing these fragments to carbon dioxide and 13 longitudinal rows of the globular protein tubulin. Remarkably,
water. Energy released from metabolism is used for ATP production, microtubules can assemble and disassemble. Microtubule assem-
which occurs at the cristae. The protein complexes that aid in the bly is regulated by the centrosome, which lies near the nucleus.
conversion of energy are located in an assembly-line fashion on The centrosome is the region of the cell that contains the centrioles.
these membranous shelves. (As noted in Table 3.1, centrioles help to form cilia, flagella, and
Every cell uses a certain amount of ATP energy to synthesize the spindle apparatus.) Microtubules radiate from the centrosome,
molecules, but many cells use ATP to carry out their special- helping to maintain the shape of the cell and acting as tracks along
ized functions. For example, muscle cells use ATP for muscle which organelles move. It is well known that during cell division,
contraction, which produces movement, and nerve cells use it microtubules form spindle fibers, which assist the movement of
for the conduction of nerve signals, which make us aware of our chromosomes.
environment. Intermediate filaments differ in structure and function.
Because they are tough and resist stress, intermediate filaments often
form cell-to-cell junctions. Intermediate filaments join skin cells in
The Cytoskeleton the outermost skin layer, the epidermis. Actin filaments are long,
Several types of filamentous protein structures form a cytoskeleton extremely thin fibers that usually occur in bundles or other groupings.
that helps maintain the cell’s shape and either anchors the organ- Actin filaments have been isolated from various types of cells, espe-
elles or assists their movement as appropriate. The cytoskeleton cially those in which movement occurs. Microvilli, which project
a. b.
Figure 3.7 Cilia and flagella. (a) Cilia are common on the surfaces of certain tissues, such as the one that forms the inner
lining of the respiratory tract. (b) Flagella form the tails of human sperm cells.
outer
microtubule
radial doublet
spoke
flagellum
triplets
shaft
basal body
cross section 100 nm
a. b.
Figure 3.8 Structure of basal bodies and flagella. (a) Basal bodies have a 9 1 0 pattern of microtubule triplets. (b) A flagellum
has a 9 1 2 pattern of microtubules.
3.2 Crossing the Plasma Membrane molecules move from high to low concentration, they are said to be
moving down their concentration gradient.) To illustrate diffusion,
9. Describe how substances move across the plasma membrane, and
distinguish between passive and active transport.
imagine putting a tablet of dye into water. The water eventually
takes on the color of the dye as the dye molecules diffuse (Fig. 3.9).
The chemical and physical properties of the plasma mem-
The plasma membrane keeps a cell intact. It allows only cer-
brane allow only a few types of molecules to enter and exit a cell
tain molecules and ions to enter and exit the cytoplasm freely;
by simple diffusion. Lipid-soluble molecules such as alcohols can
therefore, the plasma membrane is said to be selectively
diffuse through the membrane because lipids are the membrane’s
permeable (semipermeable). Both passive and active methods
main structural components. Gases can also diffuse through the
are used to cross the plasma membrane (Table 3.2). A passive
lipid bilayer; this is the mechanism by which oxygen enters cells
transport mechanism is one that doesn’t require cellular energy.
and carbon dioxide exits cells. For example, consider the move-
By contrast, active transport must be fueled by cellular energy
ment of oxygen from the lungs to the bloodstream. When you
(usually in the form of ATP).
inhale, oxygen fills the tiny air sacs, or alveoli, within your lungs.
Neighboring lung capillaries contain red blood cells with a very
Simple Diffusion low oxygen concentration. Oxygen diffuses from the area of high-
Simple diffusion is the random movement of simple atoms or mol- est concentration to the area of lowest concentration: first through
ecules from an area of higher concentration to an area of lower alveolar cells, then lung capillary cells, and finally into the red
concentration until they are equally distributed. (When atoms or blood cells.
1
You can observe filtration in a drip coffeemaker. Water moves Na
+
Na+
K+
from the area of high pressure (the water reservoir) to the area +
K+
Na
of low pressure (the coffee pot). Large substances (the coffee
grounds) remain behind in the coffee filter, but small molecules
(caffeine, flavor molecules) and water pass through.
Transport by Carriers
Most solutes do not simply diffuse across a plasma membrane;
P
rather, they are transported by means of protein carriers within the
ATP
membrane. During facilitated diffusion (facilitated transport), a Na +
molecule (e.g., an amino acid or glucose) is transported across the ADP
plasma membrane from the side of higher concentration to the side 2
Na + 3
of lower concentration. The cell doesn’t need to expend energy for K+
K+
this type of transport because the molecules are moving down their Inside
concentration gradient.
Figure 3.11 Active transport through a plasma mem-
brane. Active transport allows a molecule to cross the membrane
Begin Thinking Clinically from lower concentration to higher concentration. 1 Ion (or mol-
ecule) enters carrier. 2 Breakdown of ATP induces a change in
If the disease diabetes isn’t well controlled, the shape that 3 drives the molecule across the membrane.
concentration of glucose found in blood soars after meals.
The protein carriers can’t transport it all into cells. What
happens to that extra glucose? During active transport, a molecule is moving contrary to
Answer and discussion in Appendix A. the normal direction—that is, from lower to higher concentration
(Fig. 3.11). For example, iodine collects in the cells of the thyroid
gland; sugar is completely absorbed from the gut by cells that line the
digestive tract; and sodium (Na+) is sometimes almost completely
PASSIVE METHODS
Simple diffusion High to low concentration Concentration gradient Lipid-soluble molecules, gases
Osmosis High to low concentration Semipermeable membrane, water Absorption of water from
concentration gradient digestive tract to bloodstream
Facilitated diffusion High to low concentration Carrier molecule plus concentration gradient Sugars and amino acids
Filtration High to low pressure Pressure gradient Water and dissolved solutes out
of capillaries
ACTIVE METHODS
Active transport Low to high concentration Carrier molecule plus cell energy Ions, sugars, amino acids
Endocytosis
Phagocytosis Into the cell (“cell eating”) Vesicle formation Bacterial cells, viruses, cell
debris
Pinocytosis Into the cell (“cell drinking”) Vesicle formation Breast milk absorption in infants
Exocytosis Out of the cell Vesicle fuses with plasma membrane Hormones, messenger
chemicals, other
macromolecules
Dehydration is due to a loss of water. The solute concentration in The signs of moderate dehydration are a dry mouth, sunken eyes, and
extracellular fluid increases—that is, tissue fluid becomes hypertonic skin that will not bounce back after light pinching. If dehydration
to cells, and water leaves the cells, so that they crenate. A common becomes severe, the pulse and breathing rate are rapid, the hands and
cause of dehydration is excessive sweating, perhaps during exercise, feet are cold, and the lips are blue. Although dehydration leads to
without any replacement of the water lost. Dehydration can also be a weight loss, deliberately dehydrating to lose weight is extremely dan-
side effect of any illness that causes prolonged vomiting or diarrhea. gerous and can be fatal.
plasma
intracellular fluid 2 Solute
membrane
concentration
increases in
extracellular
fluid compartment.
nucleus extracellular fluid
a. 3 Water leaves
intracellular fluid
compartment
by osmosis.
plasma
2 Solute
membrane
concentration
of extracellular
fluid compartment
decreases.
nucleus
Figure 3A Dehydration versus water intoxication. (a) If extracellular fluid loses too much water, cells lose water by osmosis
and become dehydrated. (b) If extracellular fluid gains too much water, cells gain water by osmosis and water intoxication occurs.
Water intoxication may be caused by excessive consumption may be suffering from water intoxication. The cure, an intravenous
of pure water. The tissue fluid becomes hypotonic to the cells, and solution containing high amounts of sodium, is the opposite of that for
water enters the cells. Water intoxication can lead to pulmonary dehydration. Therefore, it is important that physicians be able to diag-
edema (excess tissue fluid in the lungs) and swelling in the brain. In nose water intoxication in athletes who have had an opportunity to
extreme cases, it is fatal. Water intoxication is not nearly as common drink fluids over a period of a few hours. To prevent both dehydration
in adults as is dehydration. It can result from a mental disorder termed and water intoxication, athletes should replace lost fluids continu-
psychogenic polydipsia. Another cause can be the intake of too much ously. Pure water is a good choice if the exercise period is short. Low-
pure water during vigorous exercise: for example, a marathon race. sodium solutions, such as sports drinks, are a good choice for
Marathoners who collapse and have nausea and vomiting after a race longer-duration events like marathons.
h
Cy
aph op
ph
Met
Te
Figure 3.13 Overview of DNA replication. During Figure 3.14 Ladder configuration and DNA replica-
replication, an old strand serves as a template for a new strand. tion. Use of the ladder configuration better illustrates how comple-
The new double helix is composed of an old (parental) strand and mentary nucleotides available in the cell pair with those of each old
a new (daughter) strand. strand before they are joined together to form a daughter strand.
nuclear pore
peptide
4. tRNAs with
C
C tRNA anticodons carry
7. tRNA departs and will C
C A amino acids
U
soon pick up another to mRNA.
mRNA. UG G U U U
anticodon
G G G A C C A A A G U A
6. Polypeptide synthesis
takes place one amino
acid at a time.
ribosome codon
5. Anticodon–codon
complementary
base pairing occurs.
Figure 3.15 Protein synthesis. The two steps required for protein synthesis are transcription, which occurs in the nucleus,
and translation, which occurs in the cytoplasm at the ribosomes.
nuclear centromere
envelope centromere
fragments
chromatin
condenses
nucleolus
disappears centromeric
spindle spindle fiber
fibers forming
polar spindle fiber
Early Prophase Prophase Early Metaphase
Centrosomes have duplicated. Nucleolus has disappeared, and Each chromatid is attached
Chromatin is condensing into duplicated chromosomes are visible. to a spindle fiber. Some
chromosomes, and the nuclear Centrosomes begin moving apart, spindle fibers stretch from each
envelope is fragmenting. and spindle is in process of forming. spindle pole and overlap.
nucleolus
centromeric
spindle fiber
Metaphase
Centromeres of duplicated chromosomes Anaphase Telophase
are aligned at the equator (center of Sister chromatids part and become daughter Daughter cells are forming
fully formed spindle). Spindle fibers chromosomes that move toward the spindle as nuclear envelopes and
attached to the sister chromatids poles. In this way, each pole receives the same nucleoli reappear. Chromosomes will
come from opposite spindle poles. number and kinds of chromosomes as the parental cell. become indistinct chromatin.
Figure 3.16 The mitotic stage of the cell cycle. Humans have 46 chromosomes; four are shown here. The blue
chromosomes were originally inherited from the father, and the red were originally inherited from the mother.
fibers to lengthen and shorten, and it ultimately causes the move- around the circumference of the cell. Actin filaments form a con-
ment of the chromosomes. tractile ring, and as the ring gets smaller and smaller, the cleavage
furrow pinches the cell in half. As a result, each cell becomes en-
closed by its own plasma membrane.
Telophase and Cytokinesis
Telophase begins when the chromosomes arrive at the poles.
During telophase, the chromosomes become indistinct chroma- Importance of Mitosis
tin again. The spindle disappears as nucleoli appear, and nu- Because of mitosis, each cell in our bodies is genetically identical,
clear envelope components reassemble in each cell. Telophase meaning that it has the same number and kinds of chromosomes.
is characterized by the presence of two distinct and separate Mitosis is important to the growth and repair of multicellular or-
daughter nuclei. ganisms. When a baby develops in the mother’s womb, mitosis oc-
Cytokinesis is division of the cytoplasm and organelles. In curs as a component of growth. As a wound heals, mitosis occurs,
human cells, a slight indentation called a cleavage furrow passes and the damage is repaired.
PROPHASE METAPHASE
aster
chromosomes
ANAPHASE TELOPHASE
Marker
9
PST Control
8
Suspect 2
FORENSIC TEST
7
Suspect 1
6
Marker
5
Evidence 2
4
Evidence 1
3
Victim
2
Marker
1
Figure 3B Actual DNA fingerprint, from a rape trial. Lanes 1, 2, 5, 8, and 9 are controls. Lane 2 is the victim’s DNA, taken
from a blood sample. Lanes 3 and 4 were created using semen samples taken from the victim’s body after the rape was
committed. Study lanes 6 and 7 carefully—who committed the crime—suspect 1 or suspect 2?
Summary
Cells differ in shape and function, but even chromosomes just prior to cell apparatus, the lysosomes, and
so, a generalized cell can be described. division. Genes, composed of various transport vesicles. The
3.1 Cellular Organization DNA, make up the chromo- ER is involved in protein
All human cells, despite varied somes, and they code for the synthesis (rough ER) and various
shapes and sizes, have a plasma production of proteins in the cy- other processes such as lipid
membrane. The plasma mem- toplasm. The nucleolus is in- synthesis (smooth ER). Mole-
brane is said to be selectively volved in ribosome formation. cules produced or modified in
permeable because it regulates C. Ribosomes are small organelles the ER are eventually enclosed
what goes through it to enter or where protein synthesis occurs. in vesicles that take them to the
leave the cell. Ribosomes occur in the cyto- Golgi apparatus. The Golgi ap-
A. The plasma membrane, plasm, both singly and in paratus processes and pack-
composed of phospholipid and groups. Numerous ribosomes ages molecules, distributes
protein molecules, regulates are attached to the endoplasmic them within the cell, and trans-
the entrance and exit of other reticulum. ports them out of the cell. Lyso-
molecules into and out of D. The endomembrane system somes are produced by the
the cell. consists of the nuclear Golgi apparatus, and their hy-
B. The nucleus contains envelope, endoplasmic drolytic enzymes digest macro-
chromatin, which condenses into reticulum (ER), the Golgi molecules from various sources.
Study Questions
1. What are the three main parts to any and lysosomes in your description. isotonic, hypotonic, and hypertonic
human cell? (p. 43) (pp. 47–48) solutions. (p. 52)
2. Describe the fluid-mosaic model of 8. Describe the structure and function of 13. What is the cell cycle? What stages
membrane structure. (pp. 45–46) mitochondria. Mention the energy occur during interphase? What
3. Describe the nucleus and its contents, molecule ATP in your description. happens during the mitotic stage?
and include the terms DNA and RNA in (p. 49) (pp. 55–60)
your description. (pp. 46–47) 9. What is the cytoskeleton? What role 14. Review the structure of DNA.
4. Describe the structure and function of does the cytoskeleton play in cells? How does this structure contribute
ribosomes. (p. 47) (pp. 49–50) to the process of DNA replication?
5. What is the endomembrane system? 10. Describe the structure and function (p. 56)
What organelles belong to this of centrioles. Mention the mitotic 15. Briefly describe the events of protein
system? (pp. 47–49) spindle in your description. synthesis. (pp. 56–58)
6. Describe the structure and function (pp. 50–51) 16. List the phases of mitosis. What
of endoplasmic reticulum (ER). Include 11. Contrast passive transport (diffusion, happens during each phase?
the terms smooth ER, rough ER, and osmosis, filtration) with active transport (pp. 58–60)
ribosomes in your description. of molecules across the plasma 17. Discuss the importance of mitosis in
(pp. 47–48) membrane. (pp. 51–53, 55) humans. (p. 59)
7. Describe the structure and function of 12. Define osmosis, and discuss the
the Golgi apparatus. Mention vesicles effects of placing red blood cells in
Learning Outcomes After you have studied this chapter, you should be able to:
4.1 Epithelial Tissue 6. Name the major types of muscular 10. Describe the way the body’s
tissue, and relate each one to a membranes are organized.
1. Describe the general characteristics particular organ.
and functions of epithelial tissue. 11. Name and describe the major types
of membranes in the body.
2. Name the major types of epithelial 4.4 Nervous Tissue
tissue, and relate each one to a
particular organ. 7. Describe the general characteristics Medical Focus
and functions of nervous tissue.
Necrotizing Fasciitis
4.2 Connective Tissue Cancer: The Traitor Inside
4.5 Extracellular Junctions, Glands,
3. Describe the general characteristics
and functions of connective tissue. and Membranes What’s New
4. Name the major types of connective 8. Describe the structure and function
Targeting the Traitor Inside
tissue, and relate each one to a of three types of extracellular
junctions. 3-D Printing to Create Complex Tissues
particular organ.
9. Describe the difference between an
4.3 Muscular Tissue exocrine and an endocrine gland,
and be able to give examples of
5. Describe the general characteristics
each one.
and functions of muscular tissue.
65
Cuboidal Epithelium
Simple cuboidal epithelium (Fig. 4.3) consists of a single layer of
cube-shaped cells attached to a basement membrane. This type of
epithelium is frequently found in glands, such as salivary glands,
the thyroid gland, and the pancreas, where its function is secre-
tion. Simple cuboidal epithelium also covers the ovaries and lines
most of the kidney tubules, the portion of the kidney where urine
free is formed. In one part of the kidney tubule, it absorbs substances
surface from the tubule, and in another part it secretes substances into
nucleus the tubule. Tubular absorption and secretion are both forms of
active transport. Thus, the cuboidal epithelial cells contain many
mitochondria, which supply the ATP needed for active transport.
Additionally, where the cells function in reabsorption, microvilli
basement membrane (tiny, fanlike folds in the plasma membrane) increase the surface
area of the cells.
Stratified cuboidal epithelium is mostly found lining the
Figure 4.3 Simple cuboidal epithelium. The cells are
larger ducts of certain glands, such as the mammary glands and
cube-shaped. Spherical nuclei tend to be centrally located.
the salivary glands. Often this tissue has only two layers.
Chapter 4 Body Tissues and Membranes 67
free surface
Columnar Epithelium the mucus to the back of the throat, where it may be either swal-
lowed or expectorated (spit out).
Simple columnar epithelium (Fig. 4.4) has cells that are lon-
ger than they are wide. They are modified to perform particular
functions. Some of these cells are goblet cells that secrete mucus
onto the free surface of the epithelium. Begin Thinking Clinically
This tissue is well known for lining digestive organs, including In long-term smokers, the pseudostratified ciliated
the small intestine, where microvilli expand the surface area and columnar epithelium in the bronchi is gradually converted
aid in absorbing the products of digestion. Simple columnar epithe- to stratified squamous epithelium. Why do you think this
lium also lines the uterine tubes. Here, many cilia project from the change occurs?
cells and propel the egg toward the uterus, or womb.
Answer and discussion in Appendix A.
Stratified columnar epithelium is not very common but does
exist in parts of the pharynx (back of the throat) and the male urethra.
Transitional Epithelium
Pseudostratified Columnar Epithelium The term transitional epithelium implies changeability, and this
Pseudostratified columnar epithelium is so named because it tissue changes in response to tension. It forms the lining of the uri-
appears to be layered (pseudo, false; stratified, layers). However, nary bladder, the ureters (tubes that carry urine from the kidneys
true layers do not exist because each cell touches the basement to the bladder), and part of the urethra (the single tube that carries
membrane. Each cell is tapered and narrow at one end; the opposite urine to the outside). All are structures that may need to stretch.
end contains the nucleus. The irregular placement of the nuclei cre- When the walls of the bladder are relaxed, the transitional epithe-
ates the appearance of several layers where only one really exists. lium consists of several layers of cuboidal cells. When the bladder
Pseudostratified ciliated columnar epithelium (Fig. 4.5) lines is distended because it is filled with urine, the epithelium stretches,
parts of the reproductive tract as well as the air passages of the and the outer cells take on a squamous appearance. It’s interesting
respiratory system, including the nasal cavities and the trachea to observe that the cells in transitional epithelium of the bladder
(windpipe) and its branches. Mucus-secreting goblet cells are scat- are physically able to slide in relation to one another, while at the
tered among the ciliated epithelial cells. A surface covering of same time forming a barrier that prevents any part of urine from
mucus traps foreign particles, and upward ciliary motion carries diffusing into the internal environment.
CARTILAGE
BONE
fibroblast
collagenous
fiber
elastic fiber
ground
substance
Figure 4.6 Loose (areolar) connective tissue. This tissue has a loose network of fibers.
plasma
membrane
fat within
adipose cell
nucleus of
adipose cell
Figure 4.7 Adipose tissue. The cells are filled with fat droplets.
collagenous
fibers
Figure 4.8 Dense regular connective tissue. Parallel bundles of collagenous fibers are closely packed.
fibroblast nucleus
Figure 4.9 Dense irregular connective tissue. Bundles of collagen fibers run in different directions, enabling the tissue to
resist or withstand multidirectional forces.
a. b. c.
chondrocyte elastic
matrix lacuna within lacuna perichondrium fibers chondrocytes chondrocytes collagen fibers lacuna
Figure 4.10 Three types of cartilage. (a) Hyaline cartilage is durable and flexible. (b) Elastic cartilage has the greatest
flexibility. (c) Fibrocartilage is the strongest type.
concentric
lamellae
central canal
osteon
LM 240x
b. spongy bone
osteocytes in lacunae
Figure 4.11 Bone tissue. (a) Compact bone, composed of osteons, forms the outside layer of bones. (b) Spongy bone,
composed of trabeculae, is found inside the bone.
plasma
buffy coat
4.3 Muscular Tissue
5. Describe the general characteristics and functions of muscular tissue.
formed elements 6. Name the major types of muscular tissue, and relate each one to a
particular organ.
LM 720x
TABLE 4.3 Classification of Muscular Tissue
Blood
Location: Type Fiber Appearance Location Control
In the blood vessels
Skeletal Striated and Attached to Voluntary
Function: cylindrical skeleton or skin
Supplies cells with nutrients and oxygen
and takes away their wastes; fights infection Smooth Nonstriated, Wall of hollow organs Involuntary
spindle-shaped (e.g., intestine,
Figure 4.12 Blood. When a blood sample is centri- urinary bladder,
fuged, the formed elements settle out below the plasma. White uterus, and blood
blood cells form a layer termed the “buffy coat” on top of red blood vessels)
cells. Plasma is the liquid portion of the blood. Red blood cells, Cardiac Striated, cylindrical Heart Involuntary
white blood cells, and platelets are called the formed elements. and branched
muscle fiber
250×
striation nucleus
400 3
smooth muscle cell nucleus
Figure 4.13 Skeletal muscle. The cells are long, Figure 4.14 Smooth muscle. The cells are spindle-
cylindrical, and multinucleated. shaped.
run the length of the muscle. They arise during development Cardiac Muscle
when several cells fuse, resulting in one fiber with multiple nu- Cardiac muscle (Fig. 4.15) is found only in the walls of the heart.
clei. The nuclei are located at the periphery of the cell, just in- Its contraction pumps blood and accounts for the heartbeat. Car-
side the plasma membrane. The fibers have alternating light and diac muscle combines features of both smooth muscle and skeletal
dark bands that give them a striated (striped) appearance. These muscle. Like skeletal muscle, it has striations, but the contraction of
bands are due to the placement of actin filaments and myosin the heart is involuntary (although the use of relaxation therapy does
filaments in the fiber, and they give skeletal muscle its strength.
Cardiac Muscle
Smooth Muscle Fiber appearance:
Smooth (visceral) muscle is so named because the arrange- Striated and branched,
single nucleus
ment of actin and myosin does not give the appearance of cross-
Location: Heart
striations. The spindle-shaped cells form layers in which the
Control: Involuntary
thick middle portion of one cell is opposite the thin ends of
adjacent cells. (A spindle is a long, pointed, oval structure.)
Consequently, the nuclei form an irregular pattern in the tissue
(Fig. 4.14).
Smooth muscle is not under conscious control and there-
fore is said to be involuntary. Smooth muscle is found in the
walls of hollow structures and organs, such as the blood vessels,
250 ×
intestines, stomach, uterus, and urinary bladder. This muscle intercalated disk nucleus
type contracts more slowly than skeletal muscle but can remain
contracted for a longer time. Contractility is an important char-
acteristic of smooth muscle, and it contracts rhythmically on its
own. However, its contraction can be modified by the nervous and
endocrine systems. Intestinal smooth muscle contracts in waves,
thereby moving food along its lumen (central cavity). When the
smooth muscle of blood vessels contracts, blood vessels constrict
and their diameter decreases. This helps to regulate blood flow
Figure 4.15 Cardiac muscle. The cells are cylindrical
but branched.
and blood pressure.
On June 30, 1924, 16-year-old Calvin Coolidge, Jr., son of the president,
strode out onto the tennis court at the White House. He was anxious to face
off against his older brother John, and was in a hurry. He'd forgotten his
socks, and chose to play the match without them. As happens to so many
of us, Cal left the tennis court with a blister on his foot. One week later, he
was dead, from what physicians of the day termed “blood poisoning.”
The precise cause of his death will never be known. Calvin Jr.
was never autopsied, and it would have been unlikely that testing
methods of that era would determine the bacterial organism that
infected him. However, medical records showed that surgery had been
performed before his death to try to stop the infection. Based on this
history, it's quite possible that young Coolidge may have been killed
by a condition called necrotizing fasciitis. This condition is most com-
monly caused by Streptococcus pyogenes, a group of dangerous
pathogenic bacteria that also cause “strep” throat. This strain of
Streptococcus is commonly referred to as “flesh-eating bacteria.”
As you know, fascia, or areolar connective tissue, binds tissues to
one another. Tissues are organized into groups by the fascia as well. Calvin Coolidge, Jr. (1908–1924).
For example, muscles in the upper and lower limbs are divided into
compartments by fascia. In necrotizing fasciitis, the Streptococcus shock. Surgery to remove dead tissue is frequently necessary to stop
bacteria enter the body through a break in the skin—a small abrasion, the spread of the bacteria. Limbs may need to be amputated. Plastic
a cut, an insect bite, or a broken blister. The person will notice that the surgery often must be performed after recovery to restore function, as
skin around the wound quickly becomes inflamed and painful. Once well as for cosmetic reasons.
infection starts, the bacteria travel extremely rapidly, using fascia Taking a very cautious approach to cleanliness is the best way to
channels to rapidly invade tissues all over the body. Poisons produced stop the disease from occurring. Frequent hand-washing is an obvious—
by the bacteria dissolve and kill connective tissues; thus the term but often neglected—way to prevent all forms of bacterial infection.
necrotizing, which means “causing death.” Victims experience a high Further, any damage to the skin must be taken seriously. Even small
fever, tremendous pain, and dehydration. If the condition progresses, cuts should be washed with soap and water, and bandaged for a short
the person goes into shock (you'll read more about shock in time until a scab begins to form. Resist the urge to “pop” a blister. Once
Chapter 12). The body's organ systems shut down, resulting in death. it opens on its own, disinfect the area thoroughly. If any symptoms of
Today, victims of necrotizing fasciitis are aggressively treated infection develop (high fever, inflammation, and pain around the wound
with antibiotics and the patient is carefully monitored for signs of area), seek medical attention as quickly as possible.
enable some people to consciously slow the heart). Further, like skel-
etal muscle, its contractions are strong, but like smooth muscle, the Content CHECK-UP!
contraction of the heart is inherent and rhythmical. Cardiac muscle 8. Match the muscle type with the characteristic:
contraction can be modified by the nervous and endocrine systems.
a. skeletal 1. striated and branched cells
Even though cardiac muscle fibers are striated, the cells dif-
fer from skeletal muscle fibers in that they have a single, centrally b. cardiac 2. no striations and spindle-shaped
placed nucleus. The cells are branched and seemingly fused to c. smooth 3. striated and multinucleate
one another, and the heart appears to be composed of one large, 9. Which muscle type or types contract on their own, without
interconnecting mass of muscle cells. Actually, cardiac muscle outside stimulation?
cells are separate and individual, but they are bound end-to-end 10. What feature binds cardiac muscle cells to one another so
at intercalated disks, areas where folded plasma membranes they contract as a unit?
between two cells contain adhesion junctions and gap junctions Answers in Appendix A.
(see page 75). These permit extremely rapid spread of contractile
stimuli so that the fibers contract almost simultaneously.
dendrite
Neuron
nucleus cell body
nucleus
cell body
Microglia
Astrocyte axon
Oligodendrocyte
myelin sheath
axon
Capillary
Figure 4.16 Nervous tissue. Neurons are surrounded by neuroglia, such as Schwann cells, which envelop axons. Only neu-
rons conduct nerve signals.
membrane
channels
4.5 Extracellular Junctions, Glands,
and Membranes
8. Describe the structure and function of three types of extracellular
junctions. b. Gap junction in smooth muscle
9. Describe the difference between an exocrine and an endocrine
gland, and be able to give examples of each one.
10. Describe the way the body’s membranes are organized. plasma
membranes
11. Name and describe the major types of membranes in the body.
cytoplasmic
plaque
intercellular
Extracellular Junctions filaments
cytoskeletal
fibers
The cells of a tissue can function in a coordinated manner when the c. Adhesion junction in cardiac muscle
plasma membranes of adjoining cells interact. The junctions that
occur between cells help cells function as a tissue. Figure 4.17 Extracellular junctions. Tissues are held together
A tight junction forms an impermeable barrier because ad- by (a) tight junctions that are impermeable; (b) gap junctions that
jacent plasma membrane proteins actually join, producing a zip- allow materials to pass from cell to cell; and (c) adhesion junc-
perlike fastening (Fig. 4.17a). In the stomach, digestive secretions tions that allow tissues to stretch.
are contained, and in the kidneys, the urine stays within kidney tu-
bules because epithelial cells are joined by tight junctions. A gap Glands
junction forms when two adjacent plasma membrane channels A gland consists of one or more cells that produce and secrete
join (Fig. 4.17b). This lends strength, but it also allows ions, sug- a product. Most glands are composed primarily of epithelium in
ars, and small molecules to pass between the two cells. Gap junc- which the cells secrete their product by exocytosis. During secre-
tions in heart and smooth muscle ensure synchronized contraction. tion, the contents of a vesicle are released when the vesicle fuses
In an adhesion junction (desmosome), the adjacent plasma mem- with the plasma membrane.
branes do not touch but are held together by extracellular fila- The mucus-secreting goblet cells within the columnar epithe-
ments firmly attached to cytoplasmic plaques, composed of dense lium lining the digestive tract are single cells (see Fig. 4.4). Glands
protein material (Fig. 4.17c). Desmosomes that join heart muscle with ducts that secrete their product onto the outer surface (e.g.,
cells prevent the cells from tearing apart during contraction. Simi- sweat glands and mammary glands) or into a cavity (e.g., pancreas)
larly, desmosomes in the cervix, the opening to the uterus (womb), are called exocrine glands. Ducts can be simple or compound, as
prevent the cervix from ripping when a woman gives birth. illustrated in Figure 4.18.
Figure 4.18
Multicellular exocrine glands.
Exocrine glands have ducts that
can be simple or compound.
Compound glands vary according
to the placement of secretory
portions.
Example: Example:
Sweat Mammary Example:
Simple gland Compound gland Compound Pancreas
The life of almost every person has been touched, either directly or then examined for cervical cancer cells. A biopsy is the removal of a
indirectly, by the specter of cancer. Cancer is not one disease, but suspect sample of tissue using a plunger-like device. A pathologist is
perhaps several hundred diseases, all sharing a common characteristic: a physician who is skilled at recognizing the abnormal characteristics
rapid, uncontrolled, and disorganized growth of tissue cells. Thus, any that allow for cancer diagnosis. If cancer is found and treated before
cell in any of the body’s tissues can be the starting point for cancer. metastasis occurs, chances for a complete cure are greatly increased.
Cancers are classified according to the type of tissue from which they Tumors can often be removed surgically, but there is always the
arise. Carcinomas, the most common type, are cancers of epithelial danger that they have metastasized. For this reason, surgery is often
tissues (skin and linings); sarcomas are cancers that arise in connec- preceded or followed by radiation therapy and/or chemotherapy to
tive tissue (muscle, bone, and cartilage); leukemias are cancers of the destroy rapidly dividing cancer cells. Radiation therapy using radio-
blood; and lymphomas are cancers of reticular connective tissue. The active protons is preferred over X ray because proton beams can be
chance of cancer occurring in a particular tissue is related to the rate of aimed directly at the tumor. Chemotherapy drugs kill actively grow-
cell division. As you know, epithelial cells reproduce at a high rate. ing cancer cells, but sometimes cancer cells become resistant to che-
That’s why carcinomas account for 90% of all human cancers. motherapy (even when several drugs are used in combination). The
In the body, a cancer cell divides to form a malignant neoplasm plasma membrane in resistant cells contains a carrier that pumps toxic
(“new tissue”), or a malignant tumor, that invades and destroys neigh- chemicals out of the cell. Researchers are testing drugs known to poi-
boring tissue. Cancer cells can also detach and spread to other sites by son the pump in an effort to restore sensitivity to chemotherapy.
invading the blood vessels or the lymphatic vessels. Through this pro- Unfortunately, both chemotherapy and radiation kill normal cells
cess, called metastasis, cancer tumors colonize healthy tissue else- as well as the cancer. The patient will suffer the negative side effects of
where in the body. By contrast, noncancerous, or benign tumors are therapy: nausea, vomiting, hair loss, weight loss, anemia, etc. Thus, the
encapsulated (surrounded by a connective tissue capsule) and stay in use of chemotherapy and radiation must be balanced carefully: strong
one place. To support their growth, cancer cells release a growth factor enough to kill cancer, but not so strong as to cause the person’s death.
that causes neighboring blood vessels to branch into the cancerous tis- The What’s New reading on page 80 describes emerging technologies
sue, a process called vascularization. Cancer development seems to that will specifically target cancer cells while sparing healthy cells.
occur by a two-step process involving (1) initiation and (2) promotion. Individuals should be aware of the seven danger signals for cancer
Cancer initiation is caused by a change, or a mutation, in the DNA (Table 4A) and inform their doctor when any one of these are observed.
(genes) of a cell, which results in runaway cell growth. Some muta- Further, the evidence is clear that the risk of certain types of cancer can
tions, such as those that result in certain forms of breast cancer, are be reduced by lifestyle changes. For example, avoiding excessive sun-
genetically inherited. Agents that are known to actually cause DNA light reduces the risk of skin cancer, and abstaining from cigarettes,
mutations are called carcinogens. Known carcinogens include viruses, cigars, and chewing tobacco reduces the risk of oral, throat, and lung
excessive radiation, and certain chemicals. For example, cigarette cancers, as well as other types of cancer. Exercise and a healthy diet are
smoke contains chemical carcinogens that may initiate cancers of the also believed to be important. Recommendations include:
lung, throat, mouth, and urinary bladder. A cancer promoter is any
1. Lowering total fat intake
influence that causes a mutated cell to start growing in an uncontrolled
2. Eating more high-fiber foods
manner. A promoter might cause a second mutation or provide the
3. Increasing consumption of foods rich in vitamins A and C
environment for cells to form a tumor. For example, evidence suggests
4. Reducing consumption of salt-cured and smoked foods
that a diet rich in saturated fats and cholesterol promotes colon cancer.
5. Including vegetables of the cabbage family in the diet
Considerable time may elapse between initiation and promotion, and
6. Consuming only moderate amounts of alcohol
this is one reason why cancer is seen more often in older people.
Cancer can be detected by physical examination, assisted by
various means of viewing the internal organs. Mammograms can TABLE 4.A Danger Signals for Cancer
detect early breast cancer using low-level X ray, and thyroid cancer is
diagnosed using radioactive iodine (see the Medical Focus on C hange in bowel or bladder habits
page 16). Specific blood tests exist for tumors that secrete a particular A sore that does not heal
chemical in the blood. For example, the level of prostate-specific anti- U nusual bleeding or discharge
gen (PSA) appears to increase in the blood according to the size of a T hickening or lump in breast or elsewhere
prostate tumor. Tissue samples can also detect early malignancy. Dur- I ndigestion or difficulty in swallowing
ing a Pap smear (named for George Papanicolaou, the Greek doctor O bvious change in wart or mole
who first described the test), a small sample of epithelial tissue lining
N agging cough or hoarseness
the cervix at the opening of the uterus is obtained using a cotton swab,
What's New
Targeting the Traitor Inside
“When you get into a tight place and everything goes against you, attack have also been observed to mutate over time, becoming increas-
till it seems as though you could not hang on a minute longer, ingly stronger and resistant to both chemotherapy and radiation. When
never give up then, for that is just the place and time that the this occurs, these older techniques don’t work, and the cancer returns.
tide will turn.”
—Harriet Beecher Stowe, novelist
Discovering the Enemy
A diagnosis of cancer is a terrifying event for anyone. Suddenly, life Increasingly, oncologists (doctors who specialize in cancer treatment)
is turned upside-down, and decisions must quickly be made about have new options to offer their patients. One rapidly improving tech-
treatment options. Radiation therapy and chemotherapy have existed nique is to begin the treatment process by identifying the exact genet-
for decades and continue to improve in effectiveness. However, these ics of the patient’s cancer cells. As you know from Focus on Forensics
techniques are comparable to “carpet-bombing” in wartime— in Chapter 3, cellular DNA can be studied by creating a “fingerprint.”
throwing many deadly bombs to blanket large areas and destroy as Once the cancer is precisely identified, targeted therapies can be
much as possible. As in a real-world conflict, chemotherapy and radi- developed. Targeted therapies are sometimes referred to as the result
ation therapy generally hit their cancer target, but they cause a lot of of “rational drug design,” because the treatments are tailored to dam-
collateral damage. Frequently, these types of treatments cause exten- age or destroy only one type of cells—the cancer cells. Normal cells
sive damage to other cells and tissues, which may be fatal. Further- are largely unharmed, survival rates increase, side effects are reduced,
more, cancer cells from the original tumor that survive the original and the patient’s quality of life is improved. —Continued
Targeted therapies work by directly interfering with cancer Now imagine vaccinating people for cancer, using tumor cell
growth and progression. These treatments may function externally vaccines that would work in a way similar to commonly used vac-
(directly on the plasma membrane, for example) or by obstructing cines. For example, to immunize a person for the viral diseases hepa-
internal metabolism. One of the first targeted therapies to be devel- titis (a liver disease) and influenza (flu), a person is injected with
oped is directed at the cell membrane estrogen receptors of breast pieces of virus. The virus segment can’t cause disease, but it does alert
cancer cells. You discovered in Chapter 2 that estrogens stimulate the immune system to fight the virus if you’re ever exposed. Recently,
the growth of all female structures. Unfortunately, breast cancer scientists developed a type of mouse cancer vaccine by mixing lab-
cells also increase their growth rate in response to estrogen. Selec- grown leukocytes with tumor cell cultures. Exposing the two cell types
tive estrogen receptor modulator (SERM) drugs block cancer cell to each other trained the leukocytes to recognize tumor cells, and the
estrogen receptors by binding to them in place of estrogen. Without activated defense cells were then injected into the mice. After a second
estrogen as a promoter, cancer cell growth slows and sometimes injection with more cancer cells, the resulting tumors in vaccinated
completely stops. You may have heard of Tamoxifen, a commonly mice were ten times smaller than those in unvaccinated mice. Much
used SERM. Similar drugs are used for prostate, thyroid, and uterine additional research and testing is needed, but human cancer vaccines
cancers, and new receptor blockers aimed at other cancers are in created using similar techniques might be possible in the future.
development.
What's New
3-D Printing to Create Complex Tissues
How would you construct a building? Start with a framework, or scaf- heart that was stripped of its cells, and then coated with human heart
fold, formed from a strong, rigid material such as wood or steel. cells. Not only did the cells grow, they beat in a coordinated way,
Around it, add layers: wood, brick, or metal, for example. Inside, much like the actual heart. Likewise, skeletal muscle cells grown on a
insulate and add some form of finishing material (for example, wood framework were able to contract.
or plaster). Now imagine a printer that will spray liquid materials— Now imagine that tissue layers could be crafted into organs. As
concrete, strong plastic materials, plaster—and build up that same you know from Chapter 1, organs are created from layers of tissues.
house layer by layer. That’s how a 3-D printer works, and many prod- However, to grow an actual organ from tissue culture layers, a com-
ucts such as automobile parts, tools, rocket components and house- plex network of blood vessels would have to be simultaneously cre-
hold items are currently being manufactured in this way. Now, ated to provide the organ with oxygen and nutrients, and to carry
bioengineers are now exploring this new technology of 3-D printing away waste. Bioengineers have now begun this organ creation pro-
to create functional tissues, layer by layer, using stem cells. Stem cells cess using 3-D printers and tissue-friendly inks called “bio-inks.”
are so-called undifferentiated cells that can “change their minds”— Each ink performed a different function: one created a scaffold, a
that is, they can form multiple types of different cells. second contained living cells, and when complete, the third created a
For several decades, scientists have been able to grow cells in weblike network of tiny hollow tubes. Each bio-ink created its layers
simple sheets, in a process called tissue culture. (As you know from in a 3-D process. When the printing was complete, a three-layer tissue
the chapter introduction, HeLa cells were the first to be easily grown was created. Most important, the network of tubes was lined with
in tissue culture.) Multiple applications are now widely used. For simple squamous epithelium, just like a capillary (the smallest blood
example, cultured cells can be grown from a burn patient’s remaining vessel) or a blood vessel lining.
healthy skin, then placed over the burned area as a skin graft. Bladder- Scientists continue to develop and improve stem cell culture
shaped epithelial linings can be created using a connective tissue techniques, and refinements in 3-D printing of tissue scaffolds will
framework coated with the patient’s own epithelial cells. The linings likely happen as well. In the future, it may soon be possible to com-
have been successfully transplanted into a patient’s existing bladder. pletely grow entire organs (such as a heart or a kidney) from the
More recently, researchers used a framework created from a mouse patient’s own stem cells.
Summary
4.1 Epithelial Tissue B. Simple cuboidal epithelium func- 4.2 Connective Tissue
Body tissues are categorized into tions in absorption and secre- In connective tissue, cells are sepa-
four types: epithelial, connective, tion. Stratified cuboidal rated by a matrix (organic ground
muscular, and nervous. Epithelial epithelium forms ducts in glands. substance plus fibers).
tissue is classified according to cell C. Simple columnar epithelium is A. Fibrous connective tissue can be
shape and the number of cell lay- found in mucous membranes. loose connective tissue, in which
ers. The cell shape can be squa- Stratified columnar epithelium is fibroblasts are separated by a
mous, cuboidal, or columnar. not common in the body. semisolid ground substance, or
Simple tissues have one layer of D. Pseudostratified columnar epi- dense connective tissue, which
cells, and stratified tissues have thelium appears stratified, but is contains bundles of collagenous
several layers. actually one cell layer thick. fibers. Adipose tissue is a type of
A. Simple squamous epithelium E. Transitional epithelial cells loose connective tissue in which
allows substances to diffuse, change shape from cuboidal to the fibroblasts enlarge and store
while stratified squamous is for squamous in response to ten- fat. Reticular connective tissue is
protection. sion placed on the tissue. found in lymphatic tissues.
Study Questions
1. What is a tissue? (p. 66) and central canal in your description. body are made up of nervous tissue?
2. Name the four major types of tissues. Describe the difference between (pp. 77–78)
(p. 66) compact and spongy bone. 9. Name three types of junctions, and
3. What are the functions of epithelial (pp. 72–73) state the function of each with exam-
tissue? Name the different kinds of 6. Describe the composition of blood, ples. (p. 78)
epithelial tissue, and give a location and give a function for each type of 10. Describe the structure of a gland.
for each. (pp. 66–68) blood cell. (p. 74) What is the difference between an
4. What are the functions of connective 7. What are the functions of muscular tis- exocrine gland and an endocrine
tissue? Name the different kinds of sue? Name the different kinds of mus- gland? (pp. 78, 80)
connective tissue, and give a location cular tissue, and give a location for 11. Name the different types of body
for each type. (pp. 69–71) each. (pp. 74–76) membranes, and associate each type
5. Contrast the structure of cartilage with 8. What types of cells does nervous with a particular location in the body.
that of bone, using the words lacunae tissue contain? Which organs in the (pp. 80, 82)
PART II
T he photograph you see at left is a microscopic image of a human hair
growing in a hair follicle, a tube-shaped accessory organ found in skin. All
human hair strands have the same basic chemistry—they’re formed from
keratin, the fibrous protein you first studied in Chapter 2. So what accounts for
the distinct hair colors and textures that you see here? Fundamentally, they’re
determined by genetic inheritance. Each color is made by combining the two
basic forms of melanin, the pigment produced by skin cells that also creates
skin color. Different blends of these two melanins create the infinite variations
of red, blonde, brown, and black color shades that are found in human hair. As
melanin production slows with age, a person develops gray hair; a complete
lack of melanin causes white hair. Your own hair’s texture is created by the
shape of your hair follicles. Rounded follicles result in straight hair, such as that
seen in many people of Asian descent. If the follicle is flatter, the hair becomes
more and more curly. So if you’re African, or African American, with very curly
hair, your flattened hair follicles are the reason for your curls. Don’t like your
hair the way it naturally is? By changing its chemistry, you can temporarily
straighten it, curl it, or change its color. You can read more about hair follicles,
hair growth, and hair loss on pages 89 and 90.
Learning Outcomes After you have studied this chapter, you should be able to:
5.1 Structure of the Skin 7. Explain what occurs in hyperthermia 5.6 Homeostasis
and hypothermia.
1. Describe the regions of the skin and 13. Explain how the integumentary
the hypodermis. system interacts with other body
5.4 Disorders of the Skin systems to ensure homeostasis.
2. Name the epidermal layers, and
describe their structure and function. 8. Name the three types of skin cancer,
and state their risk factors.
3. Describe the structure and function Medical Focus
of the dermis. 9. Describe several skin diseases, and
outline the steps by which a skin Decubitus Ulcers
wound heals.
5.2 Accessory Structures I.C.E—In Case of Emergency
10. Name and describe four types of
of the Skin burns with regard to depth. Burns
4. Describe the structure and growth of 11. Describe how the “rule of nines” may
hair and nails. be used to estimate the extent of a Medical Focus
5. List three glands of the skin, and burn. Body Art: Buyer Beware!
describe their structure and function.
5.5 Effects of Aging Human Systems Work Together
5.3 Functions of the Skin 12. Describe the anatomical and Integumentary System
6. List and describe the six major physiological changes that occur in
homeostatic functions of the skin. the integumentary system as we age.
86
hair shaft
stratum corneum
stratum lucidum
stratum granulosum
stratum spinosum
Epidermis stratum basale
free nerve endings
dermal papilla
Dermis
capillaries
sweat gland
vein
artery
Hypodermis nerve
Figure 5.1 Skin anatomy. Skin is composed of two regions: the epidermis and the dermis. The hypodermis, or s ubcutaneous
layer, is located beneath the skin.
the body. A well-developed hypodermis gives the body a rounded 5.2 Accessory Structures of the Skin
appearance and provides protective padding against external as-
4. Describe the structure and growth of hair and nails.
saults. Excessive development of adipose tissue in the hypodermis
5. List three glands of the skin, and d
escribe their structure
layer results in obesity. and function.
Content CHECK-UP! Hair, nails, and glands are structures of epidermal origin, even
1. Blood vessels can be found in: though some parts of hair and glands are located largely in the
a. the epidermis, dermis, and hypodermis. dermis.
b. the dermis only.
c. the hypodermis and the dermis.
Hair and Nails
2. Which of the following white blood cells found in the epider-
mis phagocytize microbes and stimulate the immune system? Hair is found on all body parts except the palms, soles, lips, nip-
ples, and portions of the external reproductive organs. Most of this
a. Merkel cells c. melanocytes
hair is fine and downy, but the hair on the head includes stronger
b. Langerhans cells
types as well. After puberty, when sex hormones are made in quan-
3. What is the deepest layer of the epidermis? What is the most tity, there is noticeable hair in the axillary and pubic regions of
superficial layer? both sexes. In males, a beard develops, and other parts of the body
Answers in Appendix A. may also become quite hairy. When women produce more male
sex hormone than usual, they can develop hirsutism, a condition
hair shaft
(beyond epidermis)
Epidermis hair
follicle
hair
root
sebaceous
(oil) gland
Dermis arrector
pili muscle
hair
matrix
dermal blood
vessels LM 70x
a. b.
region of
cell division
Figure 5.2 Hair follicle and hair shaft. (a) A hair grows from the base of a hair follicle where epidermal cells produce new
cells as older cells move outward and become keratinized. (b) A hair follicle and matrix magnified 70x.
Sweat Glands
Sweat glands, or sudoriferous glands, are present in all regions of
the skin. There can be as many as 90 glands per square centimeter
on the leg, 400 glands per square centimeter on the palms and soles,
and an even greater number on the fingertips. A sweat gland is tubu-
lar. The tubule is coiled, particularly at its origin within the dermis.
These glands become especially active when a person is under stress.
Two types of sweat glands are shown in Figure 5.4. Both
types secrete their products by exocytosis (see Chapter 3). Apo-
crine glands open into hair follicles in the anal region, groin,
finger dermis epidermis and armpits. These glands begin to secrete at puberty, and a
bone component of their secretion may act as a sex attractant. Eccrine
glands open onto the surface of the skin. They become active
Figure 5.3 Sagittal section of a nail. Cells produced when a person is hot, helping to lower body temperature as sweat
by the nail root become keratinized, forming the nail body.
evaporates. The sweat (perspiration) produced by these glands
sweat
pore
Epidermis sweat
gland duct
hair root
sebaceous
gland
Dermis eccrine
sweat gland
arrector pili
muscle
apocrine
sweat gland
hair follicle
Figure 5.4 Types of skin glands. Apocrine glands and eccrine glands are types of sweat glands.
Now that you understand the structure of the skin, consider the a. b.
many functions of this essential organ system.
Skin protects. First and foremost, the skin forms a defensive Figure 5.5 (a) X ray of a normal child. (b) X ray of a child with
shield over the entire body, safeguarding delicate underlying struc- rickets. Rickets develops from an improper diet and also from a
tures from physical trauma. The melanocytes in the stratum basale lack of ultraviolet (UV) light (sunlight). Under these conditions,
vitamin D does not form in the skin, which leads to a reduction in
protect the skin itself from UV radiation. Further, sebaceous gland
calcium u
ptake. Low calcium in bones weakens them and can
secretions, phagocytic Langerhans cells, and the outermost layer of
cause bowing.
dead cells all help to protect against invasion by pathogens.
Figure 5.6 Skin cancer. In each of the three types shown, the skin clearly has an abnormal appearance.
Epidermis
of skin
blood
vessel
white
Dermis
blood cells
of skin
fibroblast
White
blood cells
subcutaneous fat
a. b.
freshly healed
scab epidermis
regenerating
tissue regenerated
(epidermis) tissue
(epidermis)
scar tissue
regrowth of (fibrosis)
blood vessel
fibroblast
fibroblast
c. d.
Figure 5.7 The process of wound healing. (a) Tissue injury causes inflammation, with redness, swelling, heat, and pain. Deep
wounds rupture blood vessels, and blood fills the wound. (b) After a blood clot forms, a protective scab develops. Fibroblasts and
white blood cells migrate to the wound site. (c) New epidermis forms, and fibroblasts promote tissue regeneration. (d) Freshly
healed skin.
Burns are skin injuries that are usually caused by 9% A burn is a critical injury if: (1) Second-
heat but can also be caused by radioactive, chem- degree burns cover 25% or more of the patient’s
ical, and electrical agents. Burns account for ap- body; (2) third-degree burns cover 10% or more
proximately 1 million emergency department of the patient’s body; (3) any portion of the
visits yearly in the United States. Emergency body has a fourth-degree burn; or (4) third-
caregivers must quickly assess burn severity and degree burns occur on the face, hands, or feet.
take appropriate supportive action. Facial burns may be accompanied by lung dam-
Two criteria are used to estimate burn se- age from smoke inhalation. Burns to the hands
verity: depth and thickness. In first-degree or feet can scar, resulting in loss of joint
burns (a moderate sunburn, for example), only 36% movement.
the epidermis is affected. The person experi- The first responder’s reactions when caring
ences redness and pain, but no blisters or swell- 9% 9% for a burn patient (and for all other patients) can
ing. The pain subsides within 48–72 hours, and be summarized using the letters ABC:
the injury heals without further complications A—establish the airway. A tube may need
or scarring. Treatment involves pain manage- to be placed into the trachea (windpipe),
ment. The damaged skin peels off in about a especially if the patient might have suf-
18% 18%
week. perineum fered smoke inhalation. Smoke inhalation
Second-degree burns extend through the 1% should be suspected whenever there are
entire epidermis and part of the dermis. The per- facial burns, or if the patient has trouble
son experiences not only redness and pain, but breathing.
also blistering. The deeper the burn, the more B—make sure the person is breathing,
prevalent the blisters, which can enlarge after using artificial respiration when necessary.
the injury. Unless they become infected, superfi- If smoke inhalation is suspected, a para-
cial second-degree burns heal in 10–14 days medic will administer 100% oxygen.
without complications and with little scarring. If C—circulation must be maintained. The pa-
the burn extends deep into the dermis, it heals tient’s pulse is taken, and CPR is begun
more slowly over a period of 30–105 days. The when needed. The patient must be carefully
healing epidermis is extremely fragile, and observed for signs of shock—a dangerously
Figure 5B The “rule of nines” for
scarring is common. First- and second-degree estimating the extent of burns. low drop in blood pressure (see Chapter 12
burns are sometimes referred to as partial- for discussion of shock). A paramedic may
thickness burns. begin an IV (intravenous administration of a bal-
Third-degree burns, or full-thickness burns, destroy the entire anced salt solution) under a physician’s direction.
thickness of the skin. The surface of the wound is leathery and may be First responders must also act quickly to stop the burn. All clothing
brown or black. Pain receptors, blood vessels, sweat glands, sebaceous must be carefully removed from the body and any smoldering must be
glands, and hair follicles are destroyed. Fourth-degree burns involve extinguished. In the case of a chemical burn, the affected area is flushed
tissues down to the bone. Unless a very limited area of the body is af- continuously with water.
fected, the patient will likely not survive. The major complications resulting from severe burns are fluid
The extent of the burn must also be estimated when judging a loss, heat loss, and bacterial infection. Fluid loss is counteracted by
burn’s severity. The “rule of nines” is used to divide the body into continuous IV therapy. Heat loss is minimized by placing the burn
regions: the head and neck, 9% of the total body surface; each upper patient in a warm environment. Application of antibacterial dress-
limb, 9%; each lower limb, 18%; the front and back portions of the ings and isolation help prevent infection. As soon as possible, the
trunk, 18% each; and the perineum, which includes the anal and damaged tissue is removed and skin grafting is begun. The skin
urogenital regions, 1% (Fig. 5B). Physicians use the Lund-Browder needed for grafting is usually taken from other parts of the patient’s
chart to estimate the extent of burns in children. This system adjusts body. However, if the burned area is quite extensive, skin can be
for the fact that a child’s head is proportionally larger than an grown in the laboratory from only a few cells taken from the
adult’s. patient.
There’s no doubt about it: Body art is definitely mainstream. Tattoo- Metals (especially nickel) used in body jewelry are another
ing (the process of injecting inks into the dermal layer of the skin) and common cause for allergy. Once an allergic reaction develops, it
piercing the body are practices that have existed for thousands of typically persists for life. In such cases, the jewelry must be perma-
years in many different human cultures. In the past decade, both prac- nently removed if at all possible. Additionally, the jewelry may
tices have become commonplace in Western society as well. Actors, damage nerves or blood vessels as piercing occurs. Earlobes can
sports figures, and other celebrities can routinely be seen with visible be torn completely and require surgical repair if an earring is
tattoos, pierced navels, multiple earrings, or other forms of wearable snagged. Jewelry in and around the mouth may damage gums,
art. Moreover, tattoos keep getting larger. It’s no longer uncommon to break teeth or dentures, and interfere with chewing or swallowing.
see so-called sleeves—tattoos covering the entire arm—and facial Mouth jewelry that becomes loose may be aspirated (sucked into
and full-body tattoos as well. The most common sites for piercing the airways), where it can obstruct an airway and interfere with
remain the earlobes and ear cartilage, but noses, lips, eyebrows, breathing.
navels, tongues, and genitals are also common sites. Anyone considering body art must proceed with caution.
As these trends continue, more and more people are tempted to First, make sure you’re not under the influence of drugs or alcohol
get their own tattoo or piercing. But as recent reality shows like Bad when making such an important decision. If local, state, or provin-
Ink, Tattoo Nightmares, and America’s Worst Tattoos have shown, a cial law regulates tattoo and piercing artists, use an approved artist
tattoo can create big problems for its wearer. Individuals must con- or shop. Never try a “do-it-yourself” approach. Check the cleanli-
sider the decision to tattoo or pierce very carefully, and health-care ness of the shop and make sure that all equipment is steam-
providers must be prepared to give accurate information about both sterilized using a device called an autoclave, and that the tattoo
practices. With the increase in both tattooing and piercing, reports of inks are also sterile. Insist that the artist or piercer use sterile
complications have increased as well. gloves at all times. Don’t let the artist tattoo around or near a mole
Tattooing and piercing can result in infections because both prac- or other skin growth, as it may make it very difficult to diagnose a
tices can potentially introduce bacteria into the skin, blood vessels, or skin cancer in the future. For a piercing, make sure that jewelry is
lymphatic vessels. Complications from infection can range from appropriate: not too heavy, and made of inert metals such as gold,
minor skin irritations to life-threatening blood poisoning. Several titanium, niobium, or surgical stainless steel, which are less likely
cases on record have involved infection with resistant bacteria, which to cause allergic reactions. Keep the affected area scrupulously
are extremely dangerous because they are not killed by common anti- clean after piercing or tattooing, and touch jewelry as little as pos-
biotics. Fatalities have been reported from infections caused by both sible. Allow adequate time for healing. For example, pierced
piercing and tattooing. navels may require up to a year to heal completely. Finally, if com-
Further, the reaction of a person’s skin to tattoo ink is unpredict- plications develop (excessive pain, redness, swelling, fever, etc.),
able. Tattoo inks are not regulated by any form of federal agency, and seek medical attention promptly.
many color additives have not been approved for contact with the skin. Most important, anyone considering body art must remember
Some are inks used in paper printing or automobile paint. It is hardly that the decision may very likely be permanent. Piercings may
surprising that many tattooed individuals develop allergies to ingredi- never reclose completely and they may leave a large scar. Tattoos
ents in tattoo dyes. Allergies to tattoo inks can even develop years can change their appearance over time as the inks fade and the skin
after the procedure. Further, tattooed skin may develop unattractive stretches. And though your tattoo might possibly be removed by
granulomas: hard connective tissue nodules under the skin. Keloids— laser therapy, surgery, or dermabrasion (using a rotating wire
scars that grow beyond normal boundaries—may also develop as the brush to scrape off surface skin), such treatment is expensive. It
body reacts to chemicals in the ink. (African Americans are particu- may also leave large scars—and often, it cannot completely remove
larly susceptible to keloid formation, for reasons that are not clear.) the tattoo.
Endocrine System
Urinary System
Skin helps protect
endocrine glands. Skin helps regulate
water loss; sweat glands
Androgens activate carry on some excretion.
sebaceous glands and
help regulate hair Kidneys compensate for
growth. water loss due to
sweating; activate
vitamin D precursor
made by skin.
Cardiovascular System
Summary
5.1 Structure of the Skin cells and consist of keratinized The skin helps regulate body temper-
The skin has two regions, the epi- cells. ature. When the body is too hot, der-
dermis and the dermis. The hypo- B. Sweat glands are numerous and mal blood vessels dilate, and the
dermis lies below the skin. present in all regions of the skin. sweat glands are active. When the
A. The epidermis, the outer region Sweating helps lower the body body is cold, dermal blood vessels
of the skin, is made up of strati- temperature. Sebaceous glands constrict, and the sweat glands are
fied squamous epithelium. New are associated with a hair follicle inactive. Hyperthermia and hypother-
cells continually produced in the and secrete s ebum, which lubri- mia are two conditions that can result
stratum basale of the epidermis cates the hair and skin. Mam- when the body’s temperature regula-
are pushed outward and become mary glands located in the tory mechanism is overcome.
the keratinized cells of the stra- breasts produce milk after 5.4 Disorders of the Skin
tum corneum. The stratum lu- childbirth. A. Skin cancer, which is associated
cidum is found only in the thick 5.3 Functions of the Skin with ultraviolet radiation, occurs
skin of the palms and soles. Skin protects the body from physical in three forms. Basal cell carci-
B. The dermis, which is composed trauma and bacterial invasion. Skin noma and squamous cell carci-
of dense irregular connective helps regulate water loss and gain, noma can usually be removed
tissue, lies beneath the epider- which helps the urinary system. Also, surgically. Melanoma is the most
mis. It contains collagenous and sweat glands excrete some urea and dangerous form of skin cancer.
elastic fibers, blood vessels, and other wastes. The skin produces vita- B. The skin has regenerative pow-
nerve fibers. min D following exposure to UV ra- ers and can grow back on its own
C. The hypodermis is made up of diation. A hormone derived from if a wound is not too e
xtensive.
loose connective tissue and adi- vitamin D helps regulate calcium and 5.5 Effects of Aging
pose tissue, which insulates the phosphorus metabolism involved in Skin wrinkles with age because the
body from heat and cold. bone development. The skin con- epidermis is held less tightly, fibers
5.2 Accessory Structures of the Skin tains sensory receptors for touch, in the dermis are fewer, and the
Accessory structures of the skin pressure, pain, hot, and cold, which hypodermis has less padding. The
include hair, nails, and glands. help people to be aware of their skin has fewer blood vessels, sweat
A. Both hair and nails are produced surroundings. These r eceptors send glands, and hair follicles. Although
by the division of epidermal information to the n ervous system. pigment cells are fewer and the hair
Study Questions
1. In general, describe the two regions of 5. Describe in general the structure of 8. Name the three types of skin cancer,
the skin. (p. 87) a hair follicle and a nail. How do hair and cite the most frequent cause of
2. Describe the process by which epider- follicles and nails grow? (pp. 88–91) skin cancer. (pp. 93–94)
mal tissue continually renews itself. 6. Describe the structure and function of 9. Describe how a wound heals and how
(pp. 87–88) sweat glands and sebaceous glands. a scar forms. (pp. 94–95)
3. What function does the dermis have in (pp. 91–92) 10. Explain how to determine the severity
relation to the epidermis? (p. 88) 7. Name five functions of the skin, and of a burn. Describe the proper treat-
4. What primary role does adipose tell what system of the body is assisted ment for burns. (p. 96)
tissue play in the hypodermis? by these functions and how they con- 11. Explain three changes that happen to
(pp. 88–89) tribute to h omeostasis. (pp. 92–93, 97) the skin with age. (p. 97)
Learning Outcomes After you have studied this chapter, you should be able to:
6.1 Skeleton: Overview 10. Name the bones of the vertebral possible steps for
column and the thoracic cage. Be damage prevention.
1. Name at least five functions of the able to label diagrams of them.
skeleton. 6.5 Effects of Aging
11. Describe a typical vertebra, the atlas
2. Explain a classification of bones and axis, and the sacrum and 19. Describe the anatomical and
based on their shapes. coccyx. physiological changes that occur in
3. Describe the anatomy of bone. 12. Name the three types of ribs and the the skeletal system as we age.
Describe long bone structure, and three parts of the sternum.
compare/contrast compact bone 6.6 Homeostasis
and spongy bone. 6.3 Appendicular Skeleton 20. List and discuss six ways the skeletal
4. Describe the physiology of bone,
13. Name the bones of the pectoral system contributes to homeostasis.
including the cells involved in growth
girdle and the pelvic girdle. Be able Discuss ways the other systems
and repair, and the process of bone
to label diagrams of them. assist the skeletal system.
growth, development, and
remodeling. 14. Name the bones of the upper limb
(arm and forearm) and the lower limb I.C.E.—In Case of Emergency
5. Name and describe six types of
(thigh and leg). Be able to label
fractures, and state the four steps in Broken Bones
diagrams that include surface
fracture repair.
features.
6. List the surface features of bones,
15. Cite at least five differences between Medical Focus
and give examples where each can Osteoporosis
the female and male pelvises.
be found. Oh, My Aching Back: Surgical Options for Back
6.4 Joints (Articulations) Injuries
6.2 Axial Skeleton 16. Explain how joints are classified, and
7. Distinguish between the axial and give examples of each type of joint. Focus on Forensics
appendicular skeletons.
17. List the types of movements that Skeletal Remains
8. Name the bones of the skull, and state occur at synovial joints.
the important features of each bone.
18. Explain how damage and Human Systems Work Together
9. Describe the structure and function degeneration occurs at joints and
of the hyoid bone. Skeletal System
how it can be treated. Outline
102
The skeletal system consists of the bones (206 in adults) and joints,
along with the cartilage and ligaments that occur at the joints. a. b. d. e.
Figure 6.1 Classification of bones. (a) Long bones are longer than
Functions of the Skeleton they are wide. (b) Short bones are cube shaped; their lengths and
The skeleton carries out a number of vital functions in the body: widths are about equal. (c) Flat bones are platelike and have broad
surfaces. (d) Irregular bones have varied shapes with many places for
The skeleton supports the body. The bones of the lower limbs connections with other bones. (e) Round bones are circular.
support the entire body when we’re standing, and the pelvic
girdle supports the abdominal cavity.
The skeleton protects soft body parts. The bones of the skull pro-
compact bone. The epiphyses contain spongy bone. Beyond the
tect the brain; the rib cage protects the heart and lungs.
spongy bone is a thin shell of compact bone and, finally, a layer
The skeleton produces blood cells. All bones in the fetus have red
of hyaline cartilage called the articular cartilage. Articular car-
bone marrow that produces blood cells. In the adult, only
tilage is so named because it occurs where bones articulate (come
certain bones produce blood cells.
together to form a joint). Articulation is the joining together of
The skeleton stores minerals and fat. All bones have a matrix that
bones at a joint. The medullary cavity and the spaces of spongy
contains calcium phosphate, a source of calcium ions and
bone are lined with endosteum, a thin, fibrous membrane.
phosphate ions in the blood. Blood calcium is essential for
In infants, red bone marrow, a specialized tissue that pro-
nerves and muscles to function properly. Fat is stored in yel-
duces blood cells, is found in the medullary cavities of most bones.
low bone marrow.
In adults, red blood cell formation, called hematopoiesis, occurs
The skeleton, along with the muscles, permits flexible body
in the spongy bone of the skull, ribs, sternum (breastbone), and
movement. While articulations (joints) occur between all the
vertebrae, and in the ends of the long bones.
bones, we associate body movement in particular with the
bones of the limbs.
Compact Bone
Anatomy of a Long Bone Compact bone, or dense bone, contains many cylinder-shaped
units called osteons. Osteons are formed by concentric layers of
Bones are classified according to their shape. As the name im- matrix called lamellae. Between lamellae are lacunae, tiny cham-
plies, long bones are longer than they are wide. Short bones are bers where osteocytes (bone cells) can be found. Canaliculi are
cube shaped—that is, their lengths and widths are about equal. Flat small canals that connect lacunae. Oxygen and nutrients can pass
bones, such as those of the skull, are platelike with broad surfaces. through canaliculi to supply the osteocytes in each lacuna. The
Irregular bones have varied shapes that permit connections with matrix contains collagenous protein fibers and mineral deposits,
other bones. Round bones are circular in shape (Fig. 6.1). primarily of calcium and phosphorus salts.
A long bone, such as the one in Figure 6.2a, can be used to il- In each osteon, the lamellae and lacunae surround a single
lustrate certain principles of bone anatomy. The bone is enclosed in central canal. Canaliculi from adjacent lacunae open into the cen-
a tough, fibrous, connective tissue covering called the periosteum, tral canal, and blood vessels and nerves from the periosteum travel
which is continuous with the ligaments that join bones and the ten- within it. These same blood vessels and nerves can travel from one
dons that anchor muscles to bones. The periosteum contains blood central canal to another by way of perforating canals (Fig. 6.2).
vessels that enter the bone and supply its cells. At both ends of a Because osteocytes send cell extensions into the canaliculi, the
long bone is an expanded portion called an epiphysis ( pl., epiphy- osteocytes are connected to each other and also to the central canal.
ses); the portion between the epiphyses is called the diaphysis.
As shown in the section of an adult bone in Figure 6.2, the
diaphysis, or shaft, of a long bone, is not solid but has a medullary Spongy Bone
cavity containing yellow marrow. Yellow marrow contains large Spongy bone, or cancellous bone, contains numerous bony bars
amounts of fat. The medullary cavity is bounded at the sides by and plates, called trabeculae. Although lighter than compact bone,
lacuna
(with osteocyte) osteon
50 mm
chondrocytes matrix
in lacunae
central canal
hyaline cartilage
(articular cartilage) concentric
lamellae
epiphyseal line epiphysis
(epiphyseal LM 75x canalicu
canaliculi
growth plate in c. Compact bone
children/younger
people)
spongy bone
(contains red
bone marrow) concentric
lamellae nerve
compact bone vein artery
canaliculi
medullary central canal
cavity
(contains
yellow bone
marrow) osteon
periosteum
cellular fibrous
periosteum layer layer
Osteocyte canaliculus
blood vessel
a. lacuna nucleus
osteocyte
perforating canals d.
trabeculae of blood
spongy bone vessels
b.
Figure 6.2 Anatomy of a long bone. (a) The center shaft is the diaphysis, and the ends are epiphyses. The entire bone is covered
in periosteum, except at the epiphyses. Hyaline cartilage caps each epiphysis. Spongy bone of the epiphyses contains red bone mar-
row. The diaphysis contains yellow bone marrow surrounded by compact bone. (b) The detailed anatomy of spongy bone and com-
pact bone is shown in the enlargement. (c) Photomicrograph of compact bone. (d) An osteon is formed by concentric rings called
lamellae, and has a central canal with a nervous and blood supply. Bone cells, called osteocytes, live in lacunae.
articular
cartilage
secondary
ossification
centers
cartilaginous
model
epiphysis
spongy
diaphysis compact- bone
bone collar
primary medullary
ossification cavity
blood
center
vessel
a.
b.
c.
epiphysis
Figure 6.3 Endochondral ossification of a long bone.
(a) A cartilaginous model, surrounded by a periosteum, forms during fetal
development. (b) Osteoblasts that develop from the periosteum begin epiphyseal
d. growth
forming a compact bone collar around the diaphysis of the bone. secondary plate
(c) A primary ossification center contains spongy bone surrounded by ossification
compact bone. (d) The medullary cavity forms in the diaphysis, and the centers
secondary ossification centers develop in the epiphyses. (e) After birth, growth e.
is still possible as long as cartilage remains at the epiphyseal plates. When the
bone is fully formed, the remnant of the epiphyseal plates becomes a thin line.
Imagine how your world would change if you lived with severe back DEXA can be followed by blood and urine tests to detect high levels
pain. Not the kind that can be fixed with an Icy Hot® patch; rather, this of calcium and biochemicals that are associated with bone loss. Early
variety only responds to drugs whose side effects might include bone thinning, called osteopenia, should be aggressively treated to
dizziness and falling. And you’re terrified of falling, because you’ve restore bone density and reduce fracture risk. The most commonly
seen your friends and loved ones break bones after what should have used drugs, called bisphosphonates (Fosamax” Actonel”) inhibit
been a trivial misstep. For those with osteoporosis, this pain and fear bone-resorbing osteoclast cells. Hormone therapy is another option,
could be a daily reality. Osteoporosis is a condition caused by a reduc- but it is used less often simply because bisphosphonates are so effec-
tion in density of individual bones that make up the skeleton. These tive. Calcitonin and parathyroid hormone are the body’s two naturally
weakened bones are particularly susceptible to painful and debilitat- occurring hormones for calcium homeostasis. Calcitonin can be
ing fractures, especially at the hip, vertebrae, long bones, and pelvis. administered as a nasal spray or an injection to inhibit osteoclasts and
Complications of these fractures can be very dangerous and poten- to slow bone thinning. Parathyroid hormone is given by injection to
tially fatal to an older person. Simply managing pain often requires high-risk patients to stimulate osteoblast cells to build new bone. To
medication with serious side effects; some drugs can be addicting as slow bone loss, estrogen is used for postmenopausal women and tes-
well. Further, as you learned in Chapter 5, an older person immobi- tosterone can be given to men. However, sex hormone therapy must
lized by a fracture is prone to decubitus ulcers and may contract pneu- be carefully monitored because these hormones may trigger the
monia while hospitalized. Moreover, any bedridden person is at growth of certain reproductive tissue cancers. The breast cancer drugs
increased risk for forming a thromboembolism, an abnormal blood tamoxifen and raloxifene are also used occasionally to stimulate the
clot inside blood vessels. These clots can block arteries to the heart or growth of new bone tissue.
brain, resulting in heart attack or stroke. Whatever your age, race, or gender, there are steps you can take
Although osteoporosis can result from various disease processes, to avoid having osteoporosis when you get older. The most important
it’s essentially a disease of aging. Bones are continuously remodeled— thing you can do to protect your skeleton is to make sure your diet
built up, broken down, built up again—throughout life. In childhood, contains enough calcium. The U.S. National Institutes of Health
bone formation is greater than bone breakdown, and skeletal density advises that adults take in 1,000 mg of dietary calcium daily, accom-
increases until approximately age 25. Afterward, rates of bone forma- panied by 600 IU (international units) of vitamin D to promote cal-
tion and breakdown are roughly equal for the next two decades, until cium absorption. After age 65, your calcium intake should increase to
age 45 to 50. Then, reabsorption begins to exceed formation, and bone 1,200 mg. In addition, because older people have fewer vitamin D
density slowly decreases. Over time, men are apt to lose 25%, and receptors in the intestinal tract, you’ll need additional vitamin D as
women 35%, of bone mass. Male bones are generally denser than well: 800 IU are recommended. Get outside if you can, because the
female bones because testosterone (the male sex hormone) promotes ultraviolet energy from mild sunlight exposure allows your skin to
bone formation and doesn’t significantly decline until after about age synthesize vitamin D. If you live on or north of an imaginary line
65. In contrast, estrogen (female sex hormone), which promotes wom- drawn from Boston to Milwaukee, to Minneapolis, and then to Boise,
en’s bone formation, begins to decline at about age 45 with the onset chances are you’re not getting enough vitamin D during the winter
of menopause. These differences in hormone levels mean that women months. If this is the case, look for vitamin D found in fortified foods
are more likely than men to suffer osteoporosis. Women with a slight such as low-fat milk and cereal. Combine regular moderate exercise
build are at greatest risk, especially those of Caucasian and Asian such as walking, cycling or jogging with weight training to restore and
descent. maintain bone strength. And if you’re a smoker, quit! Cigarette toxins
If osteoporosis is detected early enough, treatment can slow or damage blood vessels, thus decreasing the blood supplied to bone. In
stop bone density decrease. Older at-risk individuals, especially post- addition, the nicotine and other chemicals from cigarette smoke
menopausal women, should be tested using dual-energy X-ray absorp- destroy osteoblasts. You can find tips to help you quit smoking in
tiometry (DEXA), a specialized exam used to measure bone density. Chapter 14.
After birth, the epiphyses of a long bone continue to grow, are still present. The rate of growth is controlled by hormones,
but soon secondary ossification centers appear in these regions. such as growth hormones and the sex hormones. Eventually, the
Here spongy bone forms and doesn’t break down. A band of epiphyseal plates become ossified, and the bone stops growing
cartilage called an epiphyseal plate remains between the pri- in length.
mary ossification center and each secondary center. The limbs Long bone growth ends when the epiphyseal plates are os-
keep increasing in length and width as long as epiphyseal plates sified, but it is possible for bones to increase their diameter by
ARTICULATING SURFACES
Condyle (kon-dile) A rounded knob of bone Occipital condyles at the base of the skull (Fig. 6.7)
Epicondyle Smaller knob above condyle Epicondyles of the femur (Fig. 6.17)
Head Large knob of bone that creates a Head of humerus (Fig. 6.13)
joint proximally
Process Creates a bar of bone Zygomatic and temporal processes of the skull
or (Figs. 6.6, 6.7)
forms a joint with a fossa Olecranon process of the ulna (Fig. 6.14)
Suture Immovable joint of the skull Coronal, sagittal, lambdoidal, squamosal sutures
(Figs. 6.5, 6.6, 6.7)
PROJECTIONS FOR MUSCLE ATTACHMENT
Crest A slender ridge Anterior crest of tibia (Fig. 6.18)
Malleolus Thickened, triangular knob Medial malleolus of tibia (Fig. 6.18)
Spine Slightly thickened ridge Spine of the scapula (Fig. 6.12)
Trochanter (tro-kan ter) Large, oval knob found only Greater and lesser trochanters (Fig. 6.17)
on the femur
Tubercle Small, round knob Greater tubercle of humerus (Fig. 6.13)
Tuberosity Large, irregular knob Tibial tuberosity (Fig. 6.18)
DEPRESSIONS AND OPENINGS
Foramen Hole in a bone Foramen magnum of the skull (Fig. 6.7)
Fossa Depression in bone Olecranon fossa of humerus (Fig. 6.13)
Meatus (me-ay tus) External opening in a canal External acoustic meatus of temporal bone (Fig. 6.6)
Sinus Hollow cavity in bone Frontal sinus in the frontal bone (Fig. 6.5)
Raising a child is always an adventure, but having an active, busy child Pain management should begin as soon as possible—fractures are
can bring its share of traumas. Wise parents don’t want to limit their very painful! Fractures are typically diagnosed with X rays, but a CT
children’s activities unless it’s necessary for safety. Lively children scan or MRI is sometimes necessary. The fracture is permanently im-
often require emergency care for bone fractures. When energetic chil- mobilized using a cast or splint. Bone repair occurs in a series of four
dren grow into adolescence, they often suffer sports-related fractures steps (Fig. 6A):
as well.
1. Hematoma—Within six to eight hours after a fracture, blood
A fracture is complete if the bone is broken through and incom-
escapes from ruptured blood vessels and forms a hematoma
plete if the bone isn’t separated into two parts. A fracture is simple if
(mass of clotted blood) in the space between the broken bones.
bone ends don’t pierce the skin and compound if skin is torn open by
2. Fibrocartilaginous callus—Tissue repair begins, and fibrocarti-
bone. When the broken ends are wedged into each other, the fracture is
lage fills the space between the ends of the broken bone.
impacted. A spiral fracture occurs when the break is ragged due to bone
3. Bony callus—Osteoblasts produce trabeculae of spongy bone
twisting. Repair of a fracture is called reduction. Closed reduction
and convert the fibrocartilaginous callus to a bony callus that
involves realigning the bone fragments into their normal position with-
joins the broken bones together and lasts about three to four
out surgery. Open reduction requires surgical repair of the bone using
months.
plates, screws, or pins.
4. Remodeling—Osteoblasts build new compact bone at the periph-
Parents or caregivers should always suspect a fracture if a child
ery, and osteoclasts reabsorb the spongy bone, creating a new
feels pain in a limb, or if the limb is swollen or bruised. If the child
medullary cavity.
can’t move the limb normally, or the limb appears deformed, a frac-
ture is also likely. Emergency care of a fracture involves immobiliza- In some ways, bone repair parallels the development of a bone.
tion of the limb. A temporary splint can be created using rolled-up However, a hematoma indicates that injury has occurred. Fibrocartilage
newspapers or magazines. Caregivers should constantly monitor the precedes the production of compact bone (instead of hyaline cartilage,
affected limb because nerves and blood vessels may be damaged by as in growing bone).
the injury. If tissues begin turning blue and/or a pulse can’t be felt, Parents and caregivers should also be aware that bone fractures
blood vessel damage might be occurring. Tingling or numbness indi- may sometimes indicate child/elder abuse. In cases where abuse is sus-
cate possible nerve damage. Treatment must begin immediately in pected, health-care professionals are required by law to investigate the
these situations. circumstances of the injury.
compact
bone at
hematoma break site
bony
(hard)
callus
periosteum
compact
bone fibrocartilaginous regenerating primary bone
(soft) callus blood vessels
a. b. c. d.
Figure 6A Repair of a broken bone. (a) A hematoma forms between the broken sections of the bone. (b) Fibrocartilage fills the
space for about three weeks. (c) Bony callus is formed by osteoblast cells. (d) Osteoclasts reabsorb the callus and create a new
medullary cavity.
Skull:
Skull:
frontal bone
parietal bone
zygomatic bone
temporal bone
maxilla occipital bone
mandible
hyoid bone
clavicle
Pectoral girdle: scapula
clavicle
humerus
scapula
Rib cage: vertebral column
sternum
ribs
costal cartilages
ulna
Pelvic girdle: radius
coxal bones
carpals
sacrum metacarpals
coccyx
phalanges
femur
patella
fibula
tibia
metatarsals
tarsals
phalanges a. b.
Figure 6.4 Major bones of the skeleton. (a) Anterior view. (b) Posterior view. The bones of the axial skeleton are shown in
blue-gray, and those of the appendicular skeleton are shown in tan.
frontal
bone
coronal
suture parietal bone
temporal bone
frontal sinus
occipital bone
crista galli squamous suture
ethmoid bone
perpendicular plate sella turcica
lambdoid suture
nasal bone
vomer
palatine bone
maxilla
foramen magnum
mandible
parietal bone
temporal bone
sphenoid bone
ethmoid bone
lacrimal bone
nasal bone
ethmoid bone
middle nasal (perpendicular plate) nasal septum
concha vomer
zygomatic bone inferior nasal concha
maxilla
alveolar processes
mandible
a.
coronal suture
frontal bone
parietal bone
squamosal suture
lambdoidal suture
squamous part sphenoid bone
of temporal bone nasal bone
temporal bone lacrimal bone
ethmoid bone
occipital bone
external acoustic meatus zygomatic bone
maxilla
mastoid process coronoid process
of mandible
styloid process
mandibular condyle
mandibular angle
zygomatic process
of temporal bone body of mandible
zygomatic arch
temporal process
of zygomatic bone
b.
Figure 6.6 Skull anatomy. (a) Anterior view. (b) Lateral view.
temporal process
of zygomatic bone
zygomatic process zygomatic arch
zygomatic bone of temporal bone
palatine bone
styloid process
sphenoid bone mandibular fossa
vomer
temporal bone
mastoid process
occipital condyle
foramen magnum
occipital bone
lambdoidal suture
a.
frontal sinus
frontal bone
crista galli
ethmoid bone
cribriform plate
sella turcica
sphenoid bone
temporal bone
foramen magnum
parietal bone
occipital bone
b.
Figure 6.7 Skull anatomy. (a) Inferior view. (b) Superior cross-sectional view.
transverse
body (“hill”) ligament
a. Superior view
axis
(C2 vertebra)
spinous process
superior articular
process spinous process c. Atlas and axis, posterosuperior view
transverse
process
lamina
vertebral Figure 6.10 Vertebrae. (a) A concept model showing
arch
pedicle the features of a typical vertebra. The vertebral arch is similar to a
“house” on a “hill” (body of the vertebra). (b) A typical vertebra.
The vertebral canal (containing the spinal cord) forms when ver-
tebrae are stacked so their vertebral foraminae sit atop one an-
other. (c) Atlas and axis, showing their interaction. The dens
(odontoid process) of the axis is the pivot around which the atlas
facets for joints with ribs body vertebral foramen
(thoracic vertebrae only)
turns, as when we shake our head and say “no.” The superior ar-
ticular processes on the axis form a joint with the inferior articular
b. Superior view processes on the atlas (not shown).
The structure of a single vertebra can be likened to a house (the C7 is the prominent vertebra, or in Latin, vertebra prominens. It’s
vertebral arch) sitting on a hill (the body of the vertebra). Pedicles an important feature that allows health-care providers to determine
are the upright walls of the house and the laminae form a slanting the transition between cervical and thoracic vertebrae. In addition,
roof. The single spinous process, or spine, is like a flagpole, and the cervical vertebrae all have an opening in the transverse process,
transverse processes are gutters projecting sideways at the corners called a transverse foramen. The vertebral arteries and veins pass
where pedicles join laminae. Each of these bony projections on an through the first six transverse foramina (C1 to C6). The vertebral
actual vertebra serves as a site for muscle attachment. In addition, arteries help to supply blood to the brain, and the veins return blood
superior and inferior articular processes form joints between an to the heart.
upper and a lower vertebra. When stacked this way, the articular The thoracic and lumbar vertebrae also have their own unique
processes create paired openings called intervertebral foramina structural features. The thoracic spines are long and slender and
on both sides of the vertebral column (see Fig. 6.8). Spinal nerves project downward. Further, the bodies and transverse processes
exit from the spinal cord through these openings and travel to both of thoracic vertebrae have articular facets, called costal facets, for
sides of the body. connecting to ribs. The lumbar spines are massive and square and
The vertebrae have regional differences. For example, as the project posteriorly.
vertebral column descends, the bodies get bigger and are better Atlas and Axis The first two cervical vertebrae are not typical
able to carry more weight. In the cervical region, the spines are (Fig. 6.10c). The atlas supports and balances the head. It has two
short and tend to have a split, or bifurcation. The exception is the depressions that articulate with the occipital condyles, allowing
C7 vertebra, whose long spinous process is clearly seen posteriorly movement of the head up and down (as though nodding “yes”). The
when a person touches his or her chin to the chest (try it!). Thus, axis has an odontoid process (also called the dens) that projects
clavicle
1
2 manubrium
3
4 body
true sternum
ribs 5
(vertebrosternal
ribs) 6
xiphoid
7 process
ribs
8
11
(vertebrochondral costal
ribs) 9 12
false cartilage
ribs 10
floating ribs
(vertebral ribs)
Figure 6.11 The rib cage. This structure includes the thoracic vertebrae, the ribs, and the sternum. The three bones that
make up the sternum are the manubrium, body, and xiphoid process. The ribs numbered 1–7 are true ribs; ribs 8–12 are false ribs. Ribs 11
and 12 are also called “floating ribs.”
Back pain is going to be an inevitable part of almost everyone’s life at vertebrae are fused together, motion and flexibility between vertebrae
some point. It might begin when you bend over to pick up a heavy are limited. Other available options seek to avoid removing the inter-
load and stand up suddenly. Perhaps it comes on gradually with those vertebral disk, and thus avoid having to fuse vertebrae. Intradiscal
extra 30 pounds you’ve put on over the last 10 years. Maybe it was electrothermal therapy (IDET) involves inserting a needle into a rup-
caused by the fall when you were ice skating and landed abruptly on tured disk. The needle is heated to high temperatures for approxi-
your posterior. Regardless of its cause, in 90% of cases, back pain will mately 20 minutes. The tissues of the disk wall become thickened in
slowly improve over time with minimal treatment. Pain management, response to the heat, and the ruptured area is sealed. A diskectomy
weight control, gentle massage, physical therapy, and exercise all and vertebral fusion won’t be necessary because the disk will be able
help to make the patient comfortable and restore mobility. In all but to heal.
about 5% of back pain cases, the pain is resolved within three months Vertebroplasty and kyphoplasty are techniques that allow com-
or less. pressed vertebrae to be lifted and separated from one another. In
Many back pain sufferers lack the patience and persistence to vertebroplasty, bone cement is directly injected into the space
allow the back to heal itself normally. These folks often inquire about between two compressed vertebrae, while in kyphoplasty, a small
surgical options to alleviate their back pain. However, back and neck balloon is inserted between the vertebrae and then inflated. Bone
surgery is recommended only in the most extreme cases. For example, cement is injected into the space created by the balloon, expanding
excessive movement of the vertebrae or compression of the spinal the existing vertebrae. Both of these techniques relieve pressure on
cord (as in a herniated disk, for example) are reasons to attempt back the trapped spinal nerve. If vertebrae are fractured (in a car accident,
surgery. Surgery may also be required for those with nerve damage for example), the same technique can be used. Artificial vertebral
caused by kyphosis, scoliosis, or fractured vertebrae. Loss of bowel disks can completely replace an intervertebral disk for some patients.
and/or bladder control, tingling in the arms or legs, or pain that The artificial disk is similar to implants used for hip and knee
spreads down arms or legs are all signs of nerve damage. implants. To install the artificial disk, the patient’s own intervertebral
Traditional surgeries include laminectomy, where the bony lam- disk is first removed, then two metal plates are surgically inserted
ina is cut from the vertebra and surgically removed (the lamina is onto the bodies of the superior and inferior vertebrae. In between, a
shown in Fig. 6.10b). This procedure can relieve pressure on a pinched polyethylene-covered titanium disk re-creates the space originally
spinal cord or spinal nerve. Removal of a herniated disk, called a occupied by the intervertebral disk and allows normal motion of the
diskectomy, is usually followed by fusion of vertebrae. However, once spinal column.
the body, and the xiphoid process. The manubrium is the supe-
rior portion of the sternum. The body is the middle and largest Content CHECK-UP!
part of the sternum, and the xiphoid process is the inferior and 6. Which of the following are cranial bones?
smallest portion of the sternum. The manubrium joins with the a. frontal
body of the sternum at an angle. This joint is an important ana-
b. sphenoid
tomical landmark because it occurs at the level of the second rib,
and therefore allows the ribs to be counted. Counting the ribs c. maxilla
is sometimes done to determine where the apex (most inferior d. a and b
portion) of the heart is located—usually between the fifth and e. all of the above
sixth ribs. 7. When you shake your head “no,” you’re moving a joint be-
The manubrium articulates with the costal cartilages of the tween two bones. What are they?
first and second ribs; the body articulates with costal cartilages of 8. The opening in the center of a vertebra where the spinal cord
the second through seventh ribs; and the xiphoid process doesn’t is located is called the _____ ______.
articulate with any ribs. 9. The most superior part of the sternum is the:
The xiphoid process is the third part of the sternum. Com-
a. xiphoid process. c. manubrium.
posed of hyaline cartilage in the child, it becomes ossified (con-
verted into bone) in the adult. The variably shaped xiphoid process b. body. d. costal cartilage.
serves as an attachment site for the diaphragm, which separates the Answers in Appendix A.
thoracic cavity from the abdominal cavity.
The appendicular skeleton contains the bones of the pectoral girdle, scapula
upper limbs, pelvic girdle, and lower limbs. sternum
Clavicles coracoid
process
The clavicles (collarbones) are slender and S-shaped (Fig. 6.12a).
Each clavicle articulates medially with the manubrium of the ster- acromion
num. This is the only place where the pectoral girdle is attached to process
the axial skeleton.
glenoid
Each clavicle also articulates with a scapula. The clavicle cavity
serves as a brace for the scapula and helps stabilize the shoulder. It spine of
is structurally weak, however, and if undue force is applied to the scapula
shoulder, the clavicle will fracture.
Scapulae
The scapulae (sing., scapula), also called the shoulder blades, are
broad bones that somewhat resemble triangles (Figs. 6.12b and c).
One reason for the pectoral girdle’s flexibility is that the scapulae
b. Right scapula, posterior view
are not joined to each other (see Fig. 6.4).
Each scapula has a spine, a thick ridge of bone found on its acromion
process
posterior surface. Note the following features as well:
coracoid
∙ acromion process, which articulates with a clavicle and process
provides a place of attachment for arm and upper back
muscles; glenoid
∙ coracoid process, which serves as a place of attachment for cavity
arm and chest muscles;
∙ glenoid cavity, which articulates with the head of the arm
bone (humerus). The arm joint’s flexibility is also a result
of the glenoid cavity being smaller than the head of the
humerus.
Upper Limb
The upper limb includes the bones of the arm (humerus), the fore-
arm (radius and ulna), and the hand (carpals, metacarpals, and c. Right scapula, anterior view
phalanges).1
Figure 6.12 The pectoral girdle. (a) Frontal view of
the pectoral girdles with the upper limbs attached. (b) Posterior
1
The term upper extremity is used to include a clavicle and scapula (of the pectoral view of the right scapula. (c) Anterior view of the right scapula.
girdle), an arm, forearm, wrist, and hand.
Radius
olecranon
The radius and ulna (see Figs. 6.12a and 6.14) are the bones process
trochlear
of the forearm. The radius is on the lateral side of the forearm coronoid notch olecranon
(the thumb side). When you turn your hand from the “palms process process
up” position to the “palms down” position, the radius crosses head of
radial trochlear
notch notch
over the ulna, so the two bones are criss-crossed. Proximally, radius
the radius has the following features: neck of coronoid
radius process
∙ head, which articulates with the capitulum of the
radial radial
humerus and fits into the radial notch of the ulna; notch
tuberosity
∙ radial tuberosity, which serves as a place of ulna
attachment for the distal tendon from the biceps radius
brachii;
shaft of
shaft of
Distally, the radius has the following features: ulna
radius
b. Ulna, proximal,
∙ ulnar notch, which articulates with the head of the lateral view
ulna;
∙ styloid process, which serves as a place of attachment
for ligaments that run to the wrist. ulnar
head of
notch
ulna
Ulna styloid styloid
The ulna is the longer bone of the forearm. Proximally, the process process
ulna has the following features: of radius of ulna
∙ coronoid process, which articulates with the coronoid a. Right radius and ulna, anterior view
fossa of the humerus when the elbow is flexed;
∙ olecranon process, the point of the elbow, articulates Figure 6.14 Right radius and ulna. (a) The head of the radius
articulates with the radial notch of the ulna. The head of the ulna articulates with
with the olecranon fossa of the humerus when the
the ulnar notch of the radius. (b) Lateral view of the proximal end of the ulna.
elbow is extended;
sacrum anterior
superior
pelvic brim
posterior iliac spine
superior ilium
true iliac spine
pelvis pubic symphysis
greater
sciatic notch
acetabulum
ischial spine
a. Female pelvis pubic arch
ischium pubis
iliac crest
ischial obturator
false pelvis foramen
tuberosity
ilium
pelvic brim
posterior anterior
sacral curvature
ischium pubis
true
pelvis acetabulum
Lateral view
obturator foramen
c. Right coxal bone, lateral view
pubis
b. Male pelvis pubic arch
Figure 6.16 The pelvis. The female pelvis is usually wider in all diameters than that of the male. (a) Female pelvis. (b) Male
pelvis. (c) Right coxal bone, lateral view.
2. The female pelvis is wider between the ischial spines and the ∙ head, which fits into the acetabulum of the coxal bone;
ischial tuberosities. ∙ greater and lesser trochanters, which provide a place of
3. The female inlet and outlet of the true pelvis are wider. attachment for the muscles of the thighs and buttocks;
4. The female pelvic cavity is more shallow, while the male ∙ linea aspera, a crest that serves as a place of attachment for
pelvic cavity is more funnel shaped. several muscles.
5. Female bones are lighter and thinner.
Distally, the femur has the following components:
6. The female pubic arch (angle at the pubic symphysis) is
wider. In females, the pubic arch resembles an inverted letter ∙ medial and lateral epicondyles, which serve as sites of
U; in males, the pubic arch resembles an inverted V. attachment for muscles and ligaments;
∙ lateral and medial condyles, which articulate with the tibia;
In addition to these differences in pelvic structure, male pelvic
∙ patellar surface, which is located between the condyles on
bones are larger and heavier, the articular ends are thicker, and the
the anterior surface, articulates with the patella, a small
points of muscle attachment may be larger.
triangular bone that protects the knee joint.
Lower Limb
The lower limb includes the bones of the thigh (femur), the knee- Tibia
cap (patella), the leg (tibia and fibula), and the foot (tarsals, meta- The tibia and fibula (Fig. 6.18) are the bones of the leg. The tibia,
tarsals, and phalanges).2 or shinbone, is medial to the fibula. It is thicker than the fibula and
bears the weight from the femur, with which it articulates. Observe
Femur the structural details of the tibia:
The femur (Fig. 6.17), or thighbone, is the longest and strongest
∙ medial and lateral condyles, which articulate with the
bone in the body. Proximally, note these structures on the femur:
femur;
2
The term lower extremity is used to include a coxal bone (of the pelvic girdle), the thigh,
∙ tibial tuberosity, where the patellar (kneecap) ligaments
kneecap, leg, ankle, and foot. attach;
shaft
linea
aspera
lateral medial
epicondyle epicondyle
medial lateral
lateral medial epicondyle epicondyle
condyle condyle
patellar medial lateral
surface condyle condyle
a. Anterior view b. Posterior view
Figure 6.17 Right femur. (a) Anterior view. (b) Posterior view.
∙ anterior crest, commonly called the shin; Distally, the lateral malleolus articulates with the talus and forms
∙ medial malleolus, the bulge of the inner ankle, which the outer bulge of the ankle. Its role is to stabilize the ankle; it does
articulates with the talus in the foot. not participate in forming the knee joint.
Fibula Foot
The fibula is lateral to the tibia and is more slender. It has a Each foot (Fig. 6.19) has an ankle, an instep, and five toes (also
head that articulates with the tibia just below the lateral condyle. called phalanges or digits).
lateral
condyle
medial
condyle distal phalanx distal
phalanx
tibial middle
tuberosity phalanges
phalanx
head of
fibula proximal
proximal phalanx phalanx
neck shaft of
tibia (great toe)
shaft of I II
fibula anterior medial III
crest cuneiform IV
fibula
tibia V metatarsal
tarsal intermediate bones
bones cuneiform
navicular lateral
cuneiform
cuboid tarsal
talus bones
lateral
medial calcaneus
malleolus
malleolus
Figure 6.18 Bones of the right leg, viewed anteriorly. Figure 6.19 The right foot, viewed superiorly.
Content CHECK-UP!
Cartilaginous Joints
10. Name the specific features on the scapula and humerus that
Where bones are joined by hyaline cartilage or fibrocartilage,
form the shoulder joint. Why is this joint relatively unstable?
the joint that forms is usually slightly movable. The ribs are
11. The acetabulum is a part of which bone?
joined to the sternum by costal cartilages, which are hyaline
a. coxal bone c. humerus cartilage (see Fig. 6.11). The epiphyseal plate that separates
b. scapula d. femur the diaphysis and epiphyses of growing bones is also a hyaline
12. Which bone forms the heel? cartilage joint. The bodies of adjacent vertebrae are separated
a. talus c. calcaneus by fibrocartilage intervertebral disks, which increase vertebral
flexibility. The pubic symphysis, the joint between the two
b. fibula d. tibia
pubic bones (see Fig. 6.16), consists largely of fibrocartilage.
Answers in Appendix A.
Due to hormonal changes, this joint becomes more flexible
during late pregnancy, allowing the pelvis to expand during
childbirth.
atlas
(C1 vertebra)
Saddle joint
I
Gliding joint
II
III IV V
ulna humerus
Condyloid joint
Hinge joint
Ball-and-socket joint
Rotation is the movement of a body part around its own axis, as Special Movements (Fig. 6.23c):
when the head is turned to answer “no” or when the arm is Inversion and eversion apply only to the feet. Inversion is turn-
twisted toward the trunk (medial rotation) and away from the ing the foot so that the sole faces inward, and eversion is
trunk (lateral rotation). turning the foot so that the sole faces outward.
Supination is the rotation of the forearm so that the palm is Elevation and depression refer to the lifting up and down, re-
upward; pronation is the opposite—the movement of the spectively, of a body part, as when you shrug your shoulders
forearm so that the palm is downward. or move your jaw up and down.
flexion
abduction
supination
flexion
adduction
abduction
extension
adduction pronation
Figure 6.23 Joint movements. (a) Angular movements increase or decrease the angle between the bones of a joint.
(b) Circular movements describe a circle or part of a circle. (c) Special movements are unique to certain joints.
Joint Damage and Repair sufferers keep moving. Without regular exercise, the muscles
Joints can be damaged, and even destroyed, by overuse or chronic around the joint will atrophy (shrink in size). Tendons and liga-
inflammation. Joint inflammation and destruction is termed ments around a joint weaken, and the bones at a joint can be
arthritis. The most common form, osteoarthritis, is caused by dislocated more easily.
deterioration of the articular cartilage of a joint. The damage might Tissue culture (growing cells outside of the patient’s body in a
be caused by chronic overuse. Typical cases of osteoarthritis are special medium) can help younger people and athletes with knee or
seen in joints of older persons after decades of heavy use, or in ankle injuries to regenerate their own hyaline cartilage. In autolo-
knee joints of football players after constant misuse and/or abuse. gous chondrocyte implantation (ACI) surgery, a piece of healthy
Rheumatoid arthritis (RA) occurs when the synovial membrane hyaline cartilage from the patient’s joint is first removed surgically.
becomes inflamed and grows thicker cartilage. RA is caused by The chondrocyte cells are grown outside the body in tissue culture
an autoimmune reaction in which the body’s immune system mis- medium, and then injected into the joint and left to grow. However,
takenly attacks the synovial membrane. RA is more common with ACI isn’t always successful, and it can’t be used for elderly or
age, but it can occur in children and younger adults. Gout, or gouty overweight patients.
arthritis, results from excessive buildup of uric acid (a metabolic When other treatments for arthritis fail, surgical replacement
waste) in the blood. Crystals of uric acid are deposited in the joints, of a joint can restore movement and relieve pain (Fig. 6.24). Knees
causing inflammation. and hips are the most common joints to be replaced, but shoulders,
Arthritis causes joint pain and stiffness. The afflicted joint is elbows, ankles, and even finger joints can be replaced with surgi-
often swollen and may feel warm to the touch. Without the protec- cal implants.
tive hyaline cartilage, exposed bone ends can grate against each After ACI or joint replacement, the patient faces a lengthy
other and cause bone destruction. On an X ray, the joint space is rehabilitation. Physical therapy after ACI will stimulate car-
thinner and narrower than normal. tilage growth without overstressing the area being repaired.
Treatment of arthritis should begin immediately to preserve In joint replacement patients, physical therapy will prevent
function. Pain management is an important first step, followed muscle degeneration and promote bone growth around the new
by physical therapy and exercise. It’s important that arthritis implant.
a. tibia b.
femur
Skeletal System Interacts with
All Organ Systems
Figure 6.24 Artificial joints in which polyethylene replaces
The bones protect the internal organs. The rib cage protects the
articular cartilage. (a) Knee. (b) Hip.
heart, lungs, and kidneys; the skull protects the brain; and the ver-
tebrae protect the spinal cord. Certain endocrine organs such as
Content CHECK-UP! the pituitary gland, pineal gland, and thymus, are also protected
by bone. The pelvic bones safeguard the pelvic reproductive struc-
13. What are the major unfused synarthrosis and amphiarthrosis tures, thus helping to make reproduction possible.
joints in a newborn? What might happen if these closed The bones assist all phases of respiration. The rib cage assists
prematurely? the breathing process, enabling oxygen to enter the blood. Red
14. The joint found at the elbow is what type of synovial joint? bone marrow produces the blood cells, including the red blood
a. hinge c. saddle cells that transport oxygen to the tissues. Without a supply of oxy-
b. ball-and-socket d. condyloid gen, the cells of the body could not efficiently produce ATP, the
primary cellular energy source.
15. The most common type of arthritis is ______, and involves the
breakdown of ______.
The bones store and release calcium needed by the muscular
and nervous systems. Hormones control the balance between the
Answers in Appendix A.
concentrations of calcium in the bones and in the blood. Calcium
ions play a major role in muscle contraction and nerve conduc-
tion. Calcium ions also help regulate cellular metabolism. Protein
6.5 Effects of Aging hormones, which cannot enter cells, are called the first messenger,
19. Describe the anatomical and physiological changes that occur in and a second messenger such as calcium ions jump-starts cellular
the skeletal system as we age. metabolism, directing it to proceed in a particular way.
The bones assist the lymphatic system and immunity. Red bone
Both cartilage and bone tend to gradually deteriorate as a person ages. marrow produces the white cells, which congregate in the lym-
The chemical nature of cartilage changes, and the bluish color typical phatic organs. White blood cells defend the body against pathogens
of young cartilage changes to an opaque, yellowish color. The chon- and cancerous cells. Without the ability to withstand foreign inva-
drocytes die, and reabsorption occurs as the cartilage undergoes cal- sion, the body may quickly succumb to disease and die.
cification, becoming hard and brittle. Calcification interferes with the The bones assist digestion. The bones used for chewing break
ready diffusion of nutrients and waste products through the matrix. food into pieces small enough to be swallowed and chemically di-
The articular cartilage may no longer function properly, and symp- gested. Without digestion, needed nutrients would not enter the body.
toms of osteoarthritis can appear. As you know, decades of constant The skeleton is necessary to locomotion. Our jointed skeleton
heavy use of a joint can speed the development of arthritis. Osteopo- forms a framework for muscle attachment, and muscle contraction
rosis, discussed in the Medical Focus on page 106, is present when causes joint movement. Thus, we can seek out and move to a more
weak and thin bones lead to fractures. However, it’s important to suitable external environment in order to maintain homeostasis.
remember that many of the degenerative changes seen in cartilage and
bone can be slowed or stopped by regular weight-bearing exercise.
Other Body Systems Interact
with the Skeletal System
Content CHECK-UP!
How do the other systems of the body help the skeletal system
16. Imagine that you have a patient whose knee joint has calcified function? The integumentary system and the muscles help the skel-
with age. What motions are most likely to be affected by this etal system protect internal organs. The digestive system absorbs
change? the calcium from food, and the plasma portion of blood transports
Answer in Appendix A. calcium from the digestive system to the bones. The endocrine
system regulates the storage of calcium in the bones, as well as
the growth of bone and other tissues. The cardiovascular system Content CHECK-UP!
transports oxygen and nutrients to bone, and wastes from bone. The
urinary and digestive systems excrete bone wastes. Movement of 17. Which organ systems must cooperate in order to store calcium
the bones would be impossible without contraction of the muscles. in the skeleton?
In these and other ways, the systems of the body help the skeletal Answer in Appendix A.
system carry out its functions.
Muscular System
Respiratory System
Bones provide attach-
ment sites for muscles;
store Ca2+ for muscle Rib cage protects lungs
function. and assists breathing;
bones provide attach-
Muscular contraction skull ment sites for muscles
causes bones to move involved in breathing.
joints; muscles help
protect bones. Gas exchange in lungs
provides oxygen and rids
body of carbon dioxide.
Cardiovascular System
Reproductive System
Rib cage protects heart;
red bone marrow produces
blood cells; bones store Bones provide support
Ca2+ for blood clotting. and protection of repro-
ductive organs.
Blood vessels deliver
nutrients and oxygen to Sex hormones influence
bones, carry away wastes. bone growth and density
in males and females.
Summary
6.1 Skeleton: Overview a medullary cavity with yellow C. Table 6.1 describes the different
A. The skeleton supports and pro- marrow and is bounded by com- surface features of bones.
tects the body; produces red pact bone. The epiphyses con- 6.2 Axial Skeleton
blood cells; serves as a store- tain spongy bone with red bone The axial skeleton lies in the midline
house for inorganic calcium and marrow that produces red blood of the body and consists of the skull,
phosphate ions and fat; and cells. Bone is a living tissue. It the hyoid bone, the vertebral
permits flexible movement. develops, grows, remodels, and column, and the thoracic cage.
B. A long bone has a shaft (diaphy- repairs itself. In all these pro- A. The skull is formed by the
sis) and two ends (epiphyses), cesses, osteoclasts break down cranium and the facial bones.
which are covered by articular bone, and osteoblasts build The cranium includes the frontal
cartilage. The diaphysis contains bone. bone, two parietal bones, one
Study Questions
1. What are five functions of the skeleton? 6. List the bones of the axial and appen- 10. What are the bones of the pectoral
(p. 103) dicular skeletons. (Fig. 6.4, pp. 109–110) girdle? Give examples to demon-
2. What are five major categories of 7. What are the bones of the cranium strate the flexibility of the pectoral
bones based on their shapes? (p. 103) and the face? Describe the special girdle. What are the special features
3. What are the parts of a long bone? features of the temporal bones, of a scapula? (p. 118)
What are some differences between sphenoid bone, and ethmoid bone. 11. Name the bones of the upper limb,
compact bone and spongy bone? (pp. 110–113) then outline the special features of
(pp. 103–105) 8. What are the parts of the vertebral these bones. (pp. 118–120)
4. How does bone grow in children, and column, and what are its curvatures? 12. What are the bones of the pelvic girdle,
how is it remodeled in all age groups? Distinguish between the atlas, axis, and what are their functions? (p. 120)
(pp. 105–107) sacrum, and coccyx. (pp. 113–116) 13. What are the false and true pelvises,
5. What are the various types of frac- 9. What are the bones of the rib and what are several differences
tures? Outline the four steps that are cage? List several functions of the rib between the male and female pel-
required for fracture repair. (p. 108) cage. (pp. 116–117) vises? (pp. 120–121)
Learning Outcomes After you have studied this chapter, you should be able to:
133
muscle fiber
2503 400 3
smooth muscle cell nucleus
2503 intercalated
striation nucleus disk nucleus
Figure 7.1 Types of muscles. The three types of muscles in the body have the appearance and characteristics shown above.
articular
cartilage
Lateral Medial
skin
superficial fascia
(adipose tissue)
nerve
vein
skeletal humerus artery
muscle deep fascia
individual
tendon muscle fascicles
fascicle muscle
deep fascia b.
fibers
perimysium
osseous endomysium
endomysium
tissue
epimysium perimysium
muscle fiber, c.s.
periosteum
(cut) fascicle, c.s.
fascicle, l.s.
a. c.
Figure 7.2 Connective tissue of a skeletal muscle. (a) Trace the connective tissue of a muscle from the endomysium to the
perimysium to the epimysium, which becomes a part of the deep fascia and from which the tendon extends to attach a muscle to the
periosteum of a bone. (b) Cross section of the arm showing the arrangement of the muscles, which are separated from the skin by fascia.
The superficial fascia contains adipose tissue. (c) Photomicrograph of muscle fascicles from the tongue where the fascicles run in
different directions. (c.s. 5 cross section; l.s. 5 longitudinal section.)
We’ve already examined the structure of skeletal muscle as seen with Myofilament Thick and thin filaments whose structure
the light microscope. As you know, skeletal muscle tissue has alternat- and functions account for muscle
striations and contractions
ing light and dark bands, giving it a striated appearance. The electron
mitochondrion
one myofibril
sarcoplasm
skeletal
muscle myofilament
cell
(fiber)
thick
filament
thin
filament
H zone
Z line A band I band
c. Sarcomeres are relaxed. d. Sarcomeres are contracted.
Myofibrils and Sarcomeres stripes, or striations, of skeletal muscle fibers are formed by the
Myofibrils are cylindrical and run the length of the muscle fiber. placement of myofilaments within the sarcomeres. A sarcomere
Each myofibril is composed of numerous sarcomeres, which are contains two types of protein myofilaments: The thick filaments
microscopic repeating units (Fig. 7.3). Each sarcomere extends are made up of a single protein called myosin. Thin filaments are
between two dark, vertical lines called Z lines. The horizontal made up of three proteins: a globular protein called actin, plus
axon of
motor neuron
neuro-
transmitter
(ACh)
b. One motor axon synaptic
goes to several vesicle
muscle fibers.
synaptic
cleft
neuro-
transmitter
(ACh)
axon terminal
synaptic vesicle folded
synaptic cleft sarcolemma
sarcolemma ACh receptor
contraction is occurring. Note that ATP has two roles in this pro- completely disappear (Fig. 7.3c and d). It’s important to note
cess: first to energize myosin, and then to break the link between that although the thin filaments slide past the thick filaments, the
myosin and actin. (A good analogy for the sliding filament action myosin filaments do the work with their power stroke. As sar-
of the myosin myofilaments in a sarcomere is a game of tug-of-war. comeres shorten, the myofibril and ultimately the entire muscle
The players on either side can be likened to myosin molecules. As fiber are shortened.
their hands grab, release, and grab the rope again, each side is pulled Contraction continues until nerve signals stop and calcium
toward the other and the distance between them is shortened.) ions are returned to their storage sites. The membranes of the
As the thin filaments slide past the thick filaments toward sarcoplasmic reticulum contain active transport proteins that
the sarcomere’s center, the entire sarcomere shortens (though pump calcium ions back into the interior of the sarcoplasmic
the thick and thin filaments themselves remain the same length). reticulum. Of course, this active transport process also requires
This causes the I band to shorten and the H zone to almost or ATP energy.
Ca2+
a. Function of Ca2+
actin filament
P ADP
myosin
filament
cross-bridge myosin head
ATP
actin
Figure 7.5 The role of actin and myosin in muscle contraction. (a) In relaxed muscle, tropomyosin covers myosin binding
sites on actin. Upon its release, calcium binds to troponin, exposing myosin binding sites. (b) After breaking down ATP into ADP and a
phosphate group P , myosin heads bind to actin filaments, forming cross-bridges. Then, a power stroke causes actin to move.
(c) A tug-of-war game is a good analogy for cross-bridges between myosin and actin. Cross-bridges form, then break and re-form. The
sarcomere, myofibril, and muscle fiber shorten.
Contraction of Cardiac Muscle contains thick and thin filaments. However, in smooth muscle these
filaments are not arranged into myofibrils that create visible stria-
The events of contraction in cardiac muscle are very similar to those
tions. Instead, thin filaments in smooth muscle are anchored directly
in skeletal muscle. However, in cardiac muscle, the calcium needed to
to the sarcolemma or to protein molecules called dense bodies.
bind to troponin comes from outside the cell as well as inside. After the
Dense bodies are scattered through the sarcoplasm. When a smooth
action potential signal in cardiac muscle, calcium diffuses into the sar-
muscle cell contracts, its fibers shorten in all directions, causing the
coplasm and triggers the release of more calcium from the sarcoplas-
cylindrical cell to become more oval in shape. In turn, the entire
mic reticulum. Once calcium has bound to troponin, cross-bridges can
smooth muscle shortens. Smooth muscle contraction occurs very
form between activated myosin and actin, just as in skeletal muscle.
slowly but can last for long periods of time without fatigue.
a. To start contracting, muscles break down b. To continue contracting, muscles either carry on cellular respiration
creatine phosphate. (preferred) or carry on fermentation, which can lead to fatigue. A
steady ATP supply is needed to support muscle contraction.
creatine phosphate breakdown O
creates creatine and ATP glucose
creatine
phosphate P ADP
pyruvate
creatine
ATP
H2O
creatine CO2
ADP phosphate P
Figure 7.6 Energy sources for muscle contraction. (a) Creatine phosphate can transfer a phosphate group to ADP to form ATP.
(b) Cellular respiration and fermentation also form ATP in muscle tissue.
ADP ATP
7.3 Muscle Responses
glucose lactate 7. Compare and contrast the behavior of an isolated muscle in the
laboratory with that of an intact muscle in the body.
The accumulation of lactate in a muscle fiber makes the sar- 8. Contrast slow-twitch, intermediate-twitch, and fast-twitch muscle fibers.
coplasm more acidic, and eventually enzymes cease to function
well. If fermentation continues longer than two or three minutes, Muscles can be studied in the laboratory in an effort to understand
cramping and fatigue set in. Cramping seems to be due to lack of how they respond when in the body.
ATP. As you recall, that is because ATP is needed to pump cal-
cium ions back into the sarcoplasmic reticulum and to break the
linkages between the actin and myosin filaments so that muscle
In the Laboratory
fibers can relax. Samples of intact muscle can be taken out of the body and stud-
ied in a laboratory, and these experiments have allowed scientists
to make some important observations about how muscle fibers
Oxygen Debt and entire muscles work. For example, an isolated muscle can be
When a muscle uses fermentation to supply its energy needs, placed in a laboratory solution that provides the ATP, nutrients,
it incurs an oxygen debt. Oxygen debt is obvious when a per- and electrolytes it needs to survive and contract. Next, it is stimu-
son continues to breathe heavily after exercising. The ability lated with an electric shock, whose voltage must be strong enough
to run up an oxygen debt is one of muscle tissue’s greatest as- to make the muscle contract. If a contraction occurs, the electrical
sets. Brain tissue cannot last nearly as long without oxygen as stimulus is called a threshold stimulus; if not, the stimulus is called
muscles can. a subthreshold stimulus. A single threshold stimulus causes the
Repaying an oxygen debt requires replenishing creatine phos- muscle to quickly contract and relax. This action—a single con-
phate supplies and disposing of lactic acid. Lactic acid can be traction that lasts only a fraction of a second—is called a muscle
changed back to a compound called pyruvic acid (or pyruvate) twitch. The mechanical force of contraction is recorded as a visual
and metabolized completely in mitochondria, or it can be sent to pattern called a myogram (Fig. 7.7a).
the liver to reconstruct glycogen. A marathon runner who has just A muscle twitch can be divided into three stages: the latent pe-
crossed the finish line is not exhausted due to oxygen debt. Instead, riod, contraction period, and relaxation period. The latent period
the runner has used up all the muscles’ glycogen supply, and prob- is the interval between the threshold stimulus and the onset of the
ably the liver’s glycogen as well. It takes about two days to replace muscle contraction. During this time, all of the events that lead up to
glycogen stores on a high-carbohydrate diet. cross-bridge formation are occurring in the cell. Acetylcholine dif-
People who train rely more heavily on cellular respiration than fuses across the neuromuscular junction and binds to receptors on the
do people who do not train. In people who train, the number of muscle, the action potential spreads over and throughout the muscle
muscle mitochondria increases, and so fermentation is not needed fibers, and calcium is released from the sarcoplasmic reticulum. The
to produce ATP. Their mitochondria can start consuming glucose contraction period follows the latent period. The muscle physically
and oxygen as soon as the ADP concentration starts rising during shortens during this period as cross-bridges are formed, and thick
muscle contraction. Because mitochondria can break down fatty and thin myofilaments slide past one another. Force generated by the
acids, instead of glucose, blood glucose is spared for the activity muscle increases. Finally, during the relaxation period, muscle force
of the brain. (The brain, unlike other organs, ordinarily utilizes decreases. The muscle returns to its former length as cross-bridges
only glucose to produce ATP.) Because less lactate is produced in break and calcium is returned to the sarcoplasmic reticulum.
people who train, the pH of the blood remains steady, and there is If a muscle twitches and then is allowed to relax in between
less oxygen debt. threshold stimuli, the resulting myogram shows a series of twitches
Force
period
because when the muscle is stimulated quickly enough, there is not
enough time between stimuli to return all the calcium to the sarco- latent
plasmic reticulum. With extra calcium in the sarcoplasm, more cross- period
bridges can be formed after each threshold stimulus. Further, repetitive
muscle contraction also generates heat as ATP is broken down to re- Stimulus Time
lease energy, and scientists believe that muscle enzymes may work
more efficiently to cause contraction when muscle fibers are warmer. a.
During summation, the muscle has less time to relax as the
rate of stimulation increases, and the muscle force becomes more
and more constant. When the muscle is stimulated very rapidly, the
muscle has no time to relax at all. This effect is called tetanus,1
or a tetanic contraction. It can be seen on the myogram as a hori-
Force
zontal line, because muscle force is constant during this period. If
stimulation continues at the same rate, tetanus will continue until
the muscle fatigues. Fatigue occurs when the muscle relaxes even
though stimulation continues, and on the myogram it can be seen
when muscle force falls. There are several reasons why isolated
Stimuli
muscles become fatigued. First, ATP is depleted during constant Time
use of a muscle; the muscle essentially “runs out of energy.” At
the same time, repetitive use causes production of lactic acid by b.
fermentation, which lowers the pH of the sarcoplasm and inhibits
muscle function. In addition, the motor nerves that supply muscle
tetanus
can run out of their neurotransmitter, acetylcholine.
summation
However, intact muscles in the body rarely fatigue completely
fatigue
like an isolated muscle in the laboratory does. Muscles are well sup-
Force
plied with blood vessels to transport nutrients and remove lactic acid.
Instead, in the body, fatigue is a gradual weakening that occurs after
repetitive use. In addition, the brain itself may signal a person to stop
exercising, even if the muscles are not truly fatigued. The mechanisms
that cause this muscle fatigue are not well understood. People who
train can exercise for longer periods without experiencing fatigue. Stimuli
Time
In the Body c.
As you know, muscles in the body are stimulated to contract by Figure 7.7. Myograms showing (a) a single twitch, (b) a series
motor nerves composed of motor neurons. The combination of the of twitches, (c) summation of twitches that produces tetanus, or
neuron and all of the muscle fibers it innervates is called a motor tetanic contraction. Muscle fatigue is caused by pH decrease and
unit. Motor units function according to a property called the all-or- depletion of muscle ATP and acetylcholine.
none law: since all the muscle fibers in a motor unit are stimulated
at once by the same neuron, they all contract simultaneously in
strength it might take to lift a pencil. Now imagine the muscular
response to the neuron, or do not contract. It’s interesting to note
effort needed to lift a book bag loaded with an entire day’s books
that the number of muscle fibers within a motor unit can be quite
and supplies. Increasing a muscle’s contraction strength can be
different. For example, in the ocular muscles that move the eyes,
accomplished by a phenomenon known as recruitment. By in-
the innervation ratio is one motor axon per 23 muscle fibers, while
creasing the intensity of nervous stimulation, the nervous system
in the gastrocnemius muscle of the leg, the ratio is about one motor
can activate, or recruit, more and more motor units, resulting in
axon per 1,000 muscle fibers. No doubt, moving the eyes requires
stronger and stronger muscle contraction. However, while some
finer control than moving the lower limbs.
muscle fibers within a muscle are contracting, others in the same
Changing the strength of a contraction occurs consciously or
muscle are relaxing. This allows a muscle to sustain a contraction
unconsciously throughout one’s day. For example, think about the
for a long period of time. In life, even when muscles appear to be
1
It’s important not to confuse normal muscle tetanus with the disease of the same name.
at rest, they exhibit tone, in which some of their fibers are always
The disease is caused by a bacterial toxin (see Medical Focus, p. 157). contracting. Muscle tone is particularly important in maintaining
posture. If all the fibers within the muscles of the neck, trunk, and Slow-Twitch and Fast-Twitch Muscle Fibers We’ve seen that
lower limbs were to suddenly relax, the body would collapse. all skeletal muscle fibers metabolize both aerobically (using
oxygen during cellular respiration) and anaerobically (without
Athletics and Muscle Contraction oxygen, using fermentation or creatine phosphate breakdown).
However, some muscle fibers utilize one method more than the
Athletes who excel in a particular sport, and much of the general
other to provide myofibrils with ATP. Slow-twitch and
public as well, are interested in staying fit by exercising. The Medi-
intermediate-twitch muscle fibers tend to be aerobic, and fast-
cal Focus on pages 155–156 outlines the importance of exercising
twitch fibers tend to be anaerobic. Slow-twitch fibers are also
throughout life, and gives suggestions for starting and staying with
referred to as type I fibers, intermediate-twitch fibers are type IIa,
an exercise program.
and fast-twitch fibers are called type IIb fibers.
Exercise and Size of Muscles Muscles that are not used or that Slow-twitch fibers have motor units with a smaller number of
are used for only very weak contractions decrease in size, or atro- fibers. These muscle fibers are most helpful in endurance sports such
phy. Atrophy can occur when a limb is placed in a cast or when the as long-distance running or swimming in a triathlon. Because they
nerve serving a muscle is damaged. If nerve stimulation is not re- produce most of their energy aerobically, they tire only when their
stored, muscle fibers are gradually replaced by fat and fibrous fuel supply is gone. Slow-twitch fibers have many mitochondria that
tissue. Unfortunately, atrophy can cause muscle fibers to shorten can maintain a steady, prolonged production of ATP when oxygen is
progressively, leaving body parts contracted in contorted positions available. An abundant supply of myoglobin, the respiratory pigment
called contractures. found in muscles, gives these fibers a dark color. They are also sur-
Forceful muscular activity over a prolonged period causes rounded by dense capillary beds for a continuous supply of blood and
muscle to increase in size as the size of the individual myofibrils oxygen. Slow-twitch fibers have a low maximum tension, which de-
within the muscle fibers increases. Increase in muscle size, called velops slowly, but these muscle fibers are highly resistant to fatigue.
hypertrophy, occurs only if the muscle contracts to at least 75% Like slow-twitch fibers, intermediate-twitch fibers are well sup-
of its maximum tension. plied with myoglobin and contain many mitochondria. Intermediate-
Some athletes take anabolic steroids, either testosterone or re- twitch fibers have an extensive blood supply as well. However, they
lated chemicals, to promote muscle growth. This practice is quite contract much more quickly and can be described as fast aerobic fibers.
dangerous and has many undesirable side effects, as discussed in Activities that require moderate strength for shorter periods (such as
the Medical Focus on pages 234–235. walking, jogging, or biking) will employ these muscles.
biceps brachii
(relaxed)
triceps brachii
(contracted)
tendon
origin
biceps brachii
(contracted)
triceps brachii
(relaxed)
radius
humerus
ulna
insertion
a. b. c.
Figure 7.8 Origin and insertion. The origin of a muscle is on a bone that remains stationary, and the insertion of a muscle is
on a bone that moves when a muscle contracts. The two muscles shown here are antagonistic. (a) When the biceps brachii and brachialis
muscles contract, they are agonists that flex the forearm. (b) Strengthening one’s arm muscles using hand weights requires forearm flex-
ion and extension. (c) When the triceps brachii contracts, it is the antagonist muscle that extends the forearm.
trapezius sternocleidomastoid
trapezius
deltoid
pectoralis major deltoid
latissimus dorsi
teres major
serratus biceps brachii
anterior triceps brachii
rectus abdominis extensor carpi
brachialis group
external external
oblique oblique
flexor carpi
group gluteus extensor
medius digitorum
Figure 7.9 (a) Anterior view of the body’s superficial skeletal muscles. (b) Posterior view of the body’s superficial skeletal muscles.
orbicularis oculi
levator labii superioris
levator anguli oris
masseter zygomaticus
buccinator
orbicularis oris
sternocleidomastoid
trapezius depressor labii inferioris
depressor anguli oris
the humeral area, whereas the radius/ulna area is referred to as the Buccinator muscles are located in the cheek areas. When a
forearm. Likewise, the femur is the thigh area, whereas the tibia/ buccinator contracts, the cheek is compressed, as when a per-
fibular area is referred to as the leg. son whistles or blows out air. Therefore, this muscle is called
After you understand the meaning of a muscle’s name, try the “trumpeter’s muscle.” Important to everyday life, the
to correlate its name with the muscle’s location and the action it buccinator helps hold food in contact with the teeth during
performs. Knowing the origin and insertion will also help you re- chewing. Babies use this muscle for suckling. It is also used
member what the muscle does. Why? Because the insertion is on in swallowing, as discussed next.
the bone that moves. You should review the various body move- Zygomaticus extends from each zygomatic arch (cheekbone) to
ments listed and illustrated in Figure 6.23. Once you’re finished, the corners of the mouth. It raises the corners of the mouth
you’ll be able to understand the actions of the muscles listed in when a person smiles.
Tables 7.2 to 7.5. Scientific terminology is necessary because it Levator anguli oris and levator labii superioris muscles lift the
allows all persons to know the exact action being described for upper edge and corners of the lip. Simultaneously contract-
that muscle. ing these muscles on both sides of the mouth helps produce a
smile. However, a person will sneer if he uses only the set on
one side of his mouth.
Muscles of the Head Depressor anguli oris and depressor labii inferioris pull the
The muscles of the head and neck, the first group of muscles we’ll lower edge and corners of the lip down, as when a person is
study, are illustrated in Figure 7.10 and listed in Table 7.2. The mus- frowning or a child is pouting.
cles of the head are responsible for facial expression and mastication
(chewing). One muscle of the head and several muscles of the neck
allow us to swallow. The muscles of the neck also move the head. Muscles of Mastication
We use the muscles of mastication when we chew food or bite
something. Although there are four pairs of muscles for chewing,
Muscles of Facial Expression only two pairs are superficial and shown in Figure 7.10. As you
The muscles of facial expression are located on the scalp and face. might expect, both pairs insert on the mandible.
These muscles are unusual in that they insert into and move the
skin. Therefore, we expect them to move the skin and not a bone. Each masseter has its origin on the zygomatic arch and its
As you know from the chapter introduction, these muscles com- insertion on the mandible. The masseter is a muscle of
municate whether we are surprised, angry, fearful, happy, and so mastication (chewing) because it is a prime mover for elevat-
forth. ing the mandible.
Each temporalis is a fan-shaped muscle that overlies the tempo-
Frontalis lies over the frontal bone; it raises the eyebrows and ral bone. It is also a prime mover for elevating the mandible.
wrinkles the brow. Frequent use results in furrowing of the The masseter and temporalis are synergists.
forehead.
Orbicularis oculi is a ringlike band of muscle that encircles
(forms an orbit about) the eye. It causes the eye to close or Muscles of the Neck
blink, and is responsible for “crow’s feet” at the eye corners. Deep muscles of the neck (not illustrated) are responsible for swal-
Orbicularis oris encircles the mouth and is used to pucker the lips, as lowing. Superficial muscles of the neck move the head (Table 7.2
in forming a kiss. Frequent use results in lines about the mouth. and Fig. 7.10).
Chapter 7 The Muscular System 147
involved in breathing. The muscles of the abdominal wall protect Muscles of the Shoulder
and support the organs within the abdominal cavity.
Muscles of the shoulder are shown in Figures 7.11 and 7.12. They
are also listed in Table 7.4. The muscles of the shoulder attach the
Muscles of the Thoracic Wall scapula to the thorax and move the scapula; they also attach the
External intercostal muscles occur between the ribs; they origi- humerus to the scapula and move the arm.
nate on a superior rib and insert on an inferior rib. These
muscles elevate the rib cage during the inspiration phase of Muscles That Move the Scapula
breathing.
Of the muscles that move the scapula, you know (from page 148)
The diaphragm is a dome-shaped muscle that, as you know,
that the trapezius adducts the scapulae.
separates the thoracic cavity from the abdominal cavity (see
Fig. 1.5). The diaphragm is the primary muscle for respira- Serratus anterior is located below the axilla (armpit) on the lat-
tion, and it is the only muscle used during normal, quiet eral chest. It runs between the upper ribs and the scapula. It
breathing. holds the scapula near the thorax, pulling it forward (as when
Internal intercostal muscles originate on an inferior rib and in- we’re pushing on something in front of us). Because this
sert on a superior rib. These muscles depress the rib cage and muscle causes a fast-forward jab of the arm, it is often called
contract only during a forced expiration. Normal expiration the boxer’s muscle. It also helps to elevate the arm above the
does not require muscular action. horizontal level.
supraspinatus
rotator cuff
deltoid infraspinatus muscles
teres minor
teres minor
serratus anterior
latissimus dorsi
external oblique
Figure 7.12 Muscles of the posterior shoulder. The right trapezius and latissimus dorsi
are removed to show the deep muscles that move the scapula, as well as three of the four rotator
cuff muscles.
Muscles That Move the Arm refers to its two heads that attach to the scapula, where it
Deltoid is a large, fleshy, triangular muscle (deltoid in Greek originates. The biceps brachii inserts on the radius.
means triangular) that covers the shoulder and causes a bulge Brachialis originates on the humerus and inserts on the ulna. It is
in the arm where it meets the shoulder. It runs from both the a muscle of the distal anterior humerus and lies deep to the
clavicle and the scapula of the pectoral girdle to the humerus. biceps brachii. It is the strongest forearm flexor muscle, and
This muscle abducts the arm to the horizontal position. the biceps brachii is its synergist.
Pectoralis major (Fig. 7.11) is a large anterior muscle of the upper Triceps brachii is the only muscle of the posterior arm
chest. It originates from a clavicle, but also from the sternum (Fig. 7.13b). As its name implies, it has three heads. The
and ribs. It inserts on the humerus. The pectoralis major flexes long head originates from the scapula and humerus, while the
the arm (raises it anteriorly). It also medially rotates and ad- medial and lateral heads only originate from the humerus.
ducts the arm, pulling it toward the chest. All three heads join in a common tendon that inserts on the
Latissimus dorsi (Fig. 7.12) is a large, wide, triangular muscle of ulna. The triceps extends the arm and forearm. The triceps is
the back. This muscle originates from the lower spine and also used in tennis to do a backhand volley.
sweeps upward to insert on the humerus. The latissimus dorsi
extends, medially rotates, and adducts the arm (brings it down Muscles of the Forearm
from a raised position). This muscle is very important for
The muscles of the forearm move the hand and fingers. They are
swimming, rowing, and climbing a rope.
illustrated in Figure 7.13c,d and listed in Table 7.4. Note that in
Rotator cuff (Figs. 7.12 and 7.13). This group of muscles is so
anatomical position, extensors of the wrists and fingers are on the
named because their tendons help form a cuff over the proximal
posterior and lateral forearm and flexors are on the anterior and
humerus. There are four rotator cuff muscles. Three are located
medial forearm.
on the posterior scapula: supraspinatus, infraspinatus, and teres
minor. The last rotator cuff muscle is the subscapularis muscle Flexor carpi and extensor carpi muscles primarily originate on
located on the anterior surface of the scapula. These muscles lie the humerus and insert on the bones of the hand. The flexor
deep to those already mentioned, and they are synergists to them. carpi flex the wrists and hands, and the extensor carpi extend
the wrists and hands.
Flexor digitorum and extensor digitorum muscles also primar-
Muscles of the Arm ily originate on the humerus and insert on the bones of the
The muscles of the arm move the forearm. They are illustrated in hand. The flexor digitorum (not shown) flexes the wrist and
Figure 7.13 and listed in Table 7.4. fingers, and the extensor digitorum extends the wrist and
fingers (i.e., the digits).
Biceps brachii is a muscle of the proximal anterior arm
(Fig. 7.13a) that is familiar because it bulges when the
forearm is flexed. It also assists in flexing the arm at the Muscles of the Hip and Lower Limb
shoulder, and supinates the hand when a doorknob is turned The muscles of the hip and lower limb are listed in Table 7.5 and
or the cap of a jar is unscrewed. The name of the muscle shown in Figures 7.14 to 7.17. These muscles, particularly those
Quadriceps femoris group Extends leg, steadies hip joint, and Ilium, femur/patellar tendon that continues as a
assists in thigh flexion ligament to tibial tuberosity
Hamstring group Flexes and rotates leg medially, Ischial tuberosity/lateral and medial tibia
and extends thigh
Gastrocnemius (găstrŏk-nē9mē-ŭs) Flexes leg; plantar flexion and Condyles of femur/calcaneus by way of Achilles tendon
eversion of foot
Tibialis anterior (tĭbē-ă9lĭs ăn-tē9rē-ōr) Dorsiflexion and inversion of foot Condyles of tibia/tarsal and metatarsal bones
Fibularis group Plantar flexion and eversion of foot Fibula/tarsal and metatarsal bones
of the hips and thigh, tend to be large and heavy because they are illustrated in Figure 7.15. (The third gluteal muscle, gluteus mini-
used to move the entire weight of the body and to resist the force of mus, is deep to both and therefore not shown in the figure.)
gravity. Therefore, they are important for movement and balance.
Gluteus maximus is the largest muscle in the body and covers
a large part of the buttock (gluteus means buttocks in Greek).
Muscles That Move the Thigh It originates at the ilium and sacrum, and inserts on the
The muscles that move the thigh have at least one origin on the femur. The gluteus maximus is a prime mover of thigh ex-
pelvic girdle and insert on the femur. Notice that the iliopsoas is tension, as when a person is walking, climbing stairs, or
an anterior muscle that moves the thigh, while the gluteal mus- jumping from a crouched position. Notice that the iliopsoas
cles (“glutes”) are posterior muscles that move the thigh. The ad- and the gluteus maximus are antagonistic muscles.
ductor muscles are medial muscles (Figs. 7.14 and 7.15). Before Gluteus medius lies partly behind the gluteus maximus
studying the action of these muscles, review the movement of the (Fig. 7.15). It runs between the ilium and the femur, and
hip joint when the thigh flexes, extends, abducts, and adducts (see functions to abduct the thigh. The gluteus maximus assists
Chapter 6, pp. 124–126). the gluteus medius in this function. Therefore, they are
synergistic muscles.
Iliopsoas (includes psoas major and iliacus) originates at the
Adductor group muscles (pectineus, adductor longus, adductor
ilium and the bodies of the lumbar vertebrae, and inserts on
magnus, gracilis) are located on the medial thigh (Fig. 7.14).
the femur medially (Fig. 7.14). This muscle is the prime
All of these muscles originate from the pubis and ischium,
mover for flexing the thigh and also the trunk, as when
and insert on the femur; the deep adductor magnus is shown
we bow. As the major flexor of the thigh, the iliopsoas is im-
in Figure 7.14. Adductor muscles adduct the thigh—that is,
portant to the process of walking. It also helps prevent the
they lower the thigh sideways from a horizontal position.
trunk from falling backward when a person is standing erect.
Because they squeeze the thighs together, these are the
The gluteal muscles form the buttocks. We will consider only muscles that keep a rider on a horse. Notice that the glutes
the gluteus maximus and the gluteus medius, both of which are and the adductor group are antagonistic muscles.
gluteus maximus
patella
patellar
fibularis ligament head of fibula
longus
tibia
fibularis
tibialis tibialis anterior
brevis gastrocnemius
anterior
extensor
digitorum fibularis longus
extensor digitorum
longus
longus
fibularis brevis
fibularis tertius
calcaneal tendon
7.7 Homeostasis
7.6 Effects of Aging 13. Describe how the muscular system works with other systems of the
12. Describe the anatomical and physiological changes that occur in the body to maintain homeostasis.
muscular system as we age.
The illustration in Human Systems Work Together on page 158
Muscle mass and strength tend to decrease as people age. How tells how the muscular system works with other systems of the
much of this is due to lack of exercise and a poor diet is under body to maintain homeostasis.
careful study. Deteriorated muscle elements are replaced initially Cardiac muscle contraction accounts for the heartbeat, which
by connective tissue and, eventually, by fat. With age, degenerative creates blood pressure, the force that propels blood in the arter-
changes take place in the mitochondria, and endurance decreases. ies and arterioles. The walls of the arteries and arterioles contain
Also, changes in the nervous and cardiovascular systems adversely smooth muscle. Constriction of arteriole walls is regulated to help
affect the structure and function of muscles. maintain blood pressure. Arterioles branch into the capillaries,
Muscle mass and strength can improve remarkably if elderly where exchange takes place that creates and cleanses tissue fluid.
people undergo a training program. Exercise at any age appears Blood and tissue fluid are the internal environment of the body, and
What’s at the top of many New Year’s resolution lists every January 1? diabetics who exercise regularly can often reduce or even eliminate
You guessed it: get more exercise! Have you ever made that resolu- the need for insulin and other medications.
tion, only to find yourself floundering and failing? Keep reading to Exercise protects your heart, blood vessels, and your brain.
learn why it’s best to stick with your New Year’s exercise plan, The life-long benefits of exercise are most apparent with regard to
instead of admitting defeat when February 1 rolls around. cardiovascular health. Regular exercise raises the blood levels of
Exercise builds muscles and saves your skeleton. Exercise high-density lipoprotein (HDL, the so-called “good cholesterol”; see
programs improve muscular strength, endurance, and flexibility. Chapter 12), and lowers blood levels of low-density lipoprotein (LDL,
Muscular strength is the force a muscle (or muscle group) can or “bad cholesterol”). These effects protect both the heart and all
exert against resistance. Muscle endurance is the muscle’s ability blood vessels—including those supplying the brain—from long-term
to contract repeatedly or to sustain a contraction for an extended damage. Thus, regular exercise reduces the risk of heart attack and
time. Muscle flexibility is tested by measuring a joint’s range of stroke.
motion. Further, it’s important to get moving to protect your brain. Exer-
As muscular strength improves, the muscle’s overall size cise can help to moderate the effects of depression because it leads to
increases. Muscle fibers synthesize more thick and thin myofila- an increase in the level of brain neurotransmitters that naturally ele-
ments, and myofibrils increase in size. Though muscle fibers don’t vate mood. Both chronic depression and poor cardiovascular health
reproduce by mitosis, they do enlarge by creating these new myofi- are strongly linked to the development of dementia, including
brils. Simultaneously, the total protein, numbers of capillaries, and Alzheimer disease.
the amounts of connective tissue, including tissue found in tendons Exercise helps prevent cancer. You know (from Chapter 4)
and ligaments, also increase. Physical training with weights can that cancer prevention requires eating properly, not smoking, and
improve muscular strength and endurance in all adults, regardless avoiding exposure to radiation and cancer-causing chemicals. To
of age. detect cancer early, when it’s most curable, you’ll need to undergo
Over time, increased muscle strength creates stronger bones appropriate medical screening tests and know the early warning
and increases joint stability. Exercise also helps prevent osteoporo- signs of cancer. But did you know that exercise also leads to a
sis, the condition described in Chapter 6 in which the bones are reduced risk of certain kinds of cancer? Evidence shows that people
weak and easily broken. Exercise stimulates the activity of osteo- who exercise are less likely to develop colon, breast, cervical, uter-
blasts (the bone building cells) in young and old alike, and even ine, and ovarian cancer.
those with joint diseases such as osteoarthritis can benefit. Patients So how do you keep that promise you made to yourself to get
who regularly exercise report much less pain, swelling, fatigue, and more exercise? Remember to use the acronym SMART as you plan
depression. your exercise routine. Studies show that successful people choose
Exercise helps control weight and keeps blood sugar con- specific and measurable goals, for starters. So instead of “exercise
centration in the normal range. Increased activity can help to take more,” maybe it’s “attend three workout classes at the gym each
off unwanted pounds and to keep them off (and that’s no surprise, week” or “take a 30-minute walk around the block five times a
right?). Moreover, glucose moves into muscle cells during contrac- week.” Activity plans must be attainable and realistic as well. If you
tion, which reduces the amount of glucose in the blood. As a result, can’t fit those three workout classes into your frantically busy life,
blood glucose homeostasis is maintained. This is extremely important why not schedule two instead, and walk in between? Realistic exer-
for your overall health, not just your waistline. Excess body weight cisers who stick with their programs also choose activities they
and elevated blood glucose levels contribute to metabolic syndrome already enjoy and will be more likely to keep doing. Finally, any
and type II diabetes, two disorders of glucose metabolism (see exercise goal must be time-limited—have a definite end time—or you
pages 230–231). Long-term complications of diabetes include kidney just might get burned out. Check out Table 7A for ways to include
failure, blindness, and cardiovascular disease. However, type II exercise in your lifestyle.
—Continued
How much time should I Vigorous activity Vigorous activity for 1 hour 3–5 days a week; Moderate exercise for
spend exercising? for 1–2 hours otherwise, 30–45 minutes of moderate 1 hour daily, 3 days a
daily activity. Can be broken up into three week; otherwise,
10–15 minute segments if needed. 30–45 minutes of daily
moderate activity. Can
be divided into three
10–15 minute segments.
Exercise at School or Work Physical education classes. Walk or cycle Taking the stairs, Taking the stairs, parking at
to school whenever possible parking at a distant a distant space, walking
space, walking or or cycling to work or to
cycling to work. volunteer activities.
Exercising at Home Free play Build muscle with Build muscle with Do daily stretching
resistance resistance exercise. exercises. Take a daily
exercise. Aerobic Aerobic exercise to walk with a dog.
exercise to prevent lower back Gardening.
control buildup pain: stretching,
of fat cells yoga
Exercising Socially Build motor skills Continue team Find exercise Try low-impact aerobics;
through team sports, dancing, partners: join a before undertaking new
sports, dance, swimming. Try a running club, exercises, consult with
swimming. new sport or bicycle club, outing your doctor.
activity. group
Innovating and Keeping it Fun Initiate family Try tennis, Take active vacations: Learn a new sport or
outings: golfing, swimming, hike, bicycle, activity: golf, fishing,
boating, horseback cross-country ski. doubles tennis, ballroom
camping, hiking riding—sports dancing
that can be
enjoyed for a
lifetime.
without cardiac and smooth muscle contraction, blood would never contraction accounts for peristalsis, the process that moves food
reach the capillaries for exchange to take place. Blood is returned to along the digestive tract. Without this action, food would never
the heart in cardiovascular veins, and excess tissue fluid is returned reach all the organs of the digestive tract where digestion releases
to the cardiovascular system within lymphatic vessels. In turn, skel- nutrients that enter the bloodstream. As part of the urinary system,
etal muscle contraction presses on the cardiovascular veins and lym- smooth muscle contracts to assist in the voiding of urine, which is
phatic vessels, and this creates the pressure that moves fluids in both necessary for ridding the body of metabolic wastes and for regulat-
types of vessels. Without the return of blood to the heart, circulation ing the blood volume, salt concentration, and pH of internal fluids.
would stop, and without the return of lymph to the blood vessels, Contraction of the skeletal muscles that are part of the respira-
normal blood pressure could not be maintained. tory system raises and lowers the rib cage and diaphragm during
The contraction of sphincters composed of smooth muscle fi- the active phases of breathing. As we breathe, oxygen enters the
bers temporarily prevents the flow of blood into a capillary. This blood and is delivered to the tissues, including the muscles, where
is an important homeostatic mechanism because in times of emer- ATP is produced in mitochondria with heat as a by-product. The
gency it is more important, for example, for blood to be directed to heat produced by skeletal muscle contraction allows the body tem-
the skeletal muscles than to the tissues of the digestive tract. perature to remain within the normal range for human beings.
Skeletal muscle in the abdominopelvic region protects all the The muscular system maintains the integrity of the skeletal
internal organs it covers. In the digestive system, smooth muscle system. Repetitive skeletal muscle contraction helps build bone,
During the course of a lifetime, nearly everyone will suffer from some infection and toxin production. Though antibiotics will kill the bacte-
type of muscular disorder. Muscular disorders cover a wide spectrum ria, once the toxin is circulating in the bloodstream, it cannot be
in terms of severity. Minor muscle irritation, inflammation, or injury removed or neutralized. Because muscles can’t relax, the patient can-
may resolve without any medical care. However, many diseases not breathe or swallow, and death may occur due to respiratory fail-
affecting the neuromuscular system are extremely serious and eventu- ure. Immunization and periodic booster shots will prevent the toxin’s
ally prove to be fatal. effects (see Immunization: The Great Protector, pages 309–310).
Spasms are sudden, involuntary muscular contractions, most Fibromyalgia is a chronic condition whose symptoms include
often accompanied by pain. Spasms can occur in both smooth and achy pain, tenderness, and stiffness of muscles. Its precise cause is not
skeletal muscles. A spasm of the intestinal tract is a “bellyache”; most known, though 80–90% of sufferers are women. Substance P, a neu-
such spasms are not serious. Multiple spasms of skeletal muscles are rotransmitter (messenger chemical) of pain pathways in the brain, has
called convulsions. Cramps are strong, painful spasms, especially of been found in the bloodstream of affected individuals. Exercise seems
the leg and foot, usually due to strenuous athletic activity. Cramps to decrease blood levels of substance P. Therapeutic massage, over-
typically occur after a strenuous workout, and may even occur when the-counter pain medication, and muscle relaxants are also
sleeping. Facial tics, such as periodic eye blinking or grimacing, are recommended.
spasms that can be controlled voluntarily but only with great effort. Muscular dystrophy is a broad term applied to a group of
Muscles, joints, and their connective tissues are often subject to disorders that causes progressive degeneration and weakening of
overuse injuries: strains, sprains, and tendinitis. A strain is caused by muscles. As muscle fibers die, fat and connective tissue take their
stretching or tearing of a muscle. A sprain is the twisting of a joint, place. Duchenne muscular dystrophy, the most common type, is
leading to swelling and injury not only of muscles but also of liga- inherited through a flawed gene carried by the mother. It is now
ments, tendons, blood vessels, and nerves. The ankle and knee are two known that the lack of a protein called dystrophin causes the condi-
areas often subject to sprains. Tendinitis is inflammation of a tendon tion. When dystrophin is absent, calcium leaks into the cell and
due to repeated athletic activity. The tendons most commonly affected activates an enzyme that dissolves muscle fibers. Treatment includes
are those associated with the shoulder, elbow, hip, and knee. muscle injections with immature muscle cells that do produce
Overuse injuries are often minor and can be treated with pain dystrophin.
medication and rest. However, an individual should seek medical Myasthenia gravis is an autoimmune disease characterized by
attention if the injured area is extremely painful, hot, or swollen, or if weakness that especially affects the muscles of the eyelids, face, neck,
accompanied by a fever. and extremities. Muscle contraction is impaired because the immune
system mistakenly produces antibodies that destroy acetylcholine
Neuromuscular Diseases receptors on the sarcolemma. (Recall that acetylcholine is the neu-
Neuromuscular disease can result from pathologic changes to the rotransmitter released by motor neurons.) In many cases, the first
muscle itself. It can also result from excessive motor nerve stimula- signs of the disease are drooping eyelids and double vision. Treatment
tion, or from damage or destruction of the motor neurons that supply includes drugs that inhibit the enzyme that digests acetylcholine, thus
the muscle. allowing it to accumulate.
The disease tetanus develops in persons who have not been Amyotrophic lateral sclerosis (ALS) is often called Lou
properly immunized against the toxin of the tetanus bacterium. Teta- Gehrig’s disease, after its most famous victim, the 1930s-era baseball
nus toxin shuts down brain areas that normally inhibit unnecessary player. ALS sufferers experience the gradual death of their motor
muscle contractions. As a result, excessive brain stimulation causes neurons, thus losing the ability to walk, talk, chew, swallow, etc. Intel-
muscles to lock in a tetanic contraction (from which the disease gets lect and sensation are not affected, however. Drugs can slow the dis-
its name). A rigidly locked jaw is one of the first signs of bacterial ease’s progression, but ALS is always fatal.
Nervous System
Digestive System
Muscle contraction
moves eyes, permits Smooth muscle
speech, creates facial contraction accounts for
expressions. peristalsis; skeletal
muscles support and
Brain controls nerves
help protect abdominal
that innervate muscles;
organs.
receptors send sensory
input from muscles to Digestive tract provides
brain. glucose for muscle acti-
vity; liver metabolizes
lactic acid following
Endocrine System anaerobic muscle
activity.
Muscles help protect
glands.
Urinary System
Androgens promote
growth of skeletal Smooth muscle
muscle; epinephrine contraction assists
stimulates heart and voiding of urine; skeletal
constricts blood vessels. muscles support and
help protect urinary
organs.
Cardiovascular System
Kidneys maintain blood
Muscle contraction levels of Na+ , K+, and
keeps blood moving in Ca2+ , which are needed
heart and blood vessels. for muscle innervation,
and eliminate creatinine.
Blood vessels deliver
nutrients and oxygen to
muscles, carry away
Reproductive System
wastes.
Muscle contraction
occurs during orgasm
and moves gametes;
abdominal and uterine
muscle contraction
occurs during childbirth.
Androgens promote
growth of skeletal
muscle.
Summary
7.1 Functions and types of muscles vessels, help protect internal or- fiber and ultimately the entire
Three types of muscle tissue are gans, and stabilize joints. muscle then shorten.
found in the body. 7.2 Microscopic Anatomy and Contrac- D. Since cardiac muscle is also stri-
A. Skeletal muscle is striated and tion of Skeletal Muscle ated, the contraction mechanism
largely voluntary, and attaches A. The muscle cell plasma mem- is very similar to that of skeletal
to the skeleton and skin. Cardiac brane, or sarcolemma, extends muscle.
muscle, found in the heart wall, into the muscle fiber to form T E. Smooth muscle has thick and
is striated, involuntary, and tubules. The sarcoplasmic reticu- thin myofilaments, but they
doesn't fatigue. Smooth muscle lum stores calcium. The arrange- aren’t arranged in a way that cre-
is involuntary, not striated, and is ment of actin and myosin ates striations.
located in the walls of internal myofilaments in a myofibril cre- F. ATP, required for muscle con-
organs and blood vessels. ates the striations of skeletal traction, can be generated by
Though it contracts slowly, it can muscle. way of creatine phosphate
sustain longer contractions. B. Skeletal muscle innervation oc- breakdown and fermentation.
B. Individual skeletal muscle cells, curs at neuromuscular junc- G. Lactic acid from fermentation
called muscle fibers, are sur- tions. Electrical signals called causes an oxygen debt because
rounded by endomysium. Bun- action potentials travel down oxygen is required to metabolize
dles of muscle fibers, called the T tubules and cause the re- this product. Cellular respiration,
fascicles, are surrounded by lease of calcium from calcium an aerobic process, is the best
perimysium. Epimysium envel- storage in the sarcoplasmic re- source of ATP.
ops the entire muscle and is ticulum. 7.3 Muscle Responses
continuous with the muscle ten- C. When calcium binds to troponin, A. In the laboratory, muscles that
don. Skeletal muscles support myosin myofilaments bind to ac- are stimulated with a single
the body, make bones move, tin myofilaments. The myosin threshold stimulus will contract
help maintain a constant body power stroke causes actin to in a twitch. The occurrence of a
temperature, assist movement in slide past myosin, shortening muscle twitch or tetanic contrac-
cardiovascular and lymphatic sarcomere length. The muscle tion depends on the frequency
Study Questions
1. Name and describe the three types of 6. What is the difference between a sin- 11. Which muscles of the neck flex and ex-
muscles, and give a general location gle muscle twitch, summation, and a tend the head? (pp. 147–148)
for each type. (pp. 134–135) tetanic contraction? (pp. 142–143) 12. What are the muscles of the thoracic
2. List and discuss five functions of skel- 7. What is the all-or-none law? What is wall? What are the muscles of the ab-
etal muscles. (p. 136) muscle tone? How does muscle dominal wall? (pp. 148–149)
3. Describe the anatomy of a muscle, contraction affect muscle size? 13. Which of the muscles of the shoulder
from the whole muscle to the myofila- (pp. 143–145) and upper limb move the arm and fore-
ments within a sarcomere. Name the 8. Describe how muscles are attached to arm, and what are their actions? Name
layers of fascia that cover a skeletal bones. Define the terms prime mover, the muscles that move the hand and
muscle and divide the muscle interior. synergist, agonist, and antagonist. (p. 145) fingers. (pp. 149–151)
(pp. 135–138) 9. How do muscles get their names? Give 14. Which of the muscles of the hip move
4. List the sequential events that occur an example for each characteristic used the thigh, and what are their actions?
after a nerve signal reaches a muscle. in naming muscles. (p. 146) Which of the muscles of the thigh
(pp. 138–140) 10. Which of the muscles of the head are move the leg, and what are their ac-
5. How is ATP supplied to muscles? What used for facial expression? Which are tions? Which of the muscles of the leg
is oxygen debt? (pp. 140–142) used for chewing? (pp. 147–148) move the feet? (pp. 151–154)
PART III
B e careful about how quickly you eat that ice cream, or you’ll get a “brain
freeze”! The trigeminal nerve, one of twelve paired cranial nerves, is part
of this phenomenon. Scientists believe that “brain freeze”—a brief, stabbing
headache caused by very cold food or beverages—occurs because cold
narrows blood vessels on the roof of the mouth and in the forehead. It’s the job
of the trigeminal nerve to react to cold, signaling brain blood vessels to widen
and carry warm blood to the “frozen” area. However, the wider blood vessels
stimulate pain nerves in nearby tissues. The response is the trigeminal nerve’s
way of telling you to slow down while you eat. You can read more about the
trigeminal nerve on page 181.
Learning Outcomes After you have studied this chapter, you should be able to:
8.1 Nervous System 9. Name the twelve pairs of cranial Visual Focus
nerves, and give a function for each.
1. Describe the three functions of the Synapse Structure and Function
nervous system. 10. Name several peripheral nerves, and
describe the spinal nerves which
2. Describe the structure of a neuron combine to create each one. Explain Medical Focus
and the functions of the three types the function of each of these
of neurons. Research on Alzheimer Disease:
peripheral nerves. Causes, Treatments, Prevention, and Hope
3. Explain how a nerve signal is 11. Describe the structure of a reflex for a Cure
conducted along a nerve and across arc and the function of a reflex
a synapse. action. What’s New
12. Define and describe the autonomic
8.2 Central Nervous System nervous system.
Epidural Stimulation in Spinal Cord Injuries:
Cause for Hope
4. Describe the three layers of 13. Distinguish between the
meninges, and state the functions of Brain in a Petri Dish: A Human Model for
sympathetic and parasympathetic Alzheimer Research
the meninges. divisions in four ways, and give
5. Describe the location and function of examples of their respective effects
cerebrospinal fluid. on specific organs. I.C.E. — In Case of Emergency
6. Describe in detail the structure of the Traumatic Brain Injury
spinal cord, and state its functions. 8.4 Effects of Aging
7. Outline the major parts of the brain 14. Describe the anatomical and Visual Focus
and the lobes of the cerebral cortex. physiological changes that occur in Autonomic System Structure and Function
State functions for each structure. the nervous system as we age.
Human Systems Work Together
8.3 Peripheral Nervous System 8.5 Homeostasis Nervous System
8. Describe the structure of a nerve, 15. Describe how the nervous system
and distinguish between sensory, works with other systems of the
motor, and mixed nerves.
Medical Focus
body to maintain homeostasis.
Parkinson’s Disease
162
cervical spinal
nerves
spinal cord Peripheral Nervous System (PNS)
sympathetic parasympathetic
division division
“fight or flight” “rest and digest”
a. b.
Figure 8.1 Organization of the nervous system in humans. (a) This pictorial representation shows the central nervous s ystem
(CNS; composed of brain and spinal cord) and some of the nerves of the peripheral nervous system (PNS). (b) The CNS and PNS communi-
cate with each other. Somatic sensory and visceral sensory nerves carry information to the brain and spinal cord. Somatic motor nerves signal
skeletal muscles and autonomic motor nerves signal smooth muscle, cardiac muscle, and glands.
Nervous Tissue
b. Interneuron
Although exceedingly complex, nervous tissue is made up of just
two principal types of cells: (1) neurons, also called nerve cells, 400 nm
which generate and transmit nerve signals; and (2) neuroglia,
which nourish and support neurons (see Chapter 4, pp. 77–78). axon
Neuron Structure
dendrite
Neurons vary in appearance, but all of them have just three parts:
a cell body, dendrite(s), and an axon. As shown in Figure 8.2, the
c. Motor neuron
cell body of each type of neuron contains the nucleus, as well as
other organelles. Dendrites are shorter, highly branched extensions cell body
that receive signals from sensory receptors or other neurons. At the
dendrites, incoming signals can result in neuron signals that are con-
ducted toward the neuron cell body. Neuron signals are then transmit-
ted away from the cell body by a single axon. Every axon branches
into many fine endings, each tipped by a small swelling called an
axon
axon terminal. (You’ll remember from Chapter 7 that axon terminals
are found at the neuromuscular junction. There they release the ace-
tylcholine neurotransmitter to start a muscle action potential.) node of Ranvier
Axons can be grouped together in bundles. A bundle of par-
allel axons in the peripheral nervous system is called a nerve,
whereas a similar axon bundle in the central nervous system is a
tract. Axons found in nerves or in tracts may be covered by cells 2.7 µm
containing myelin, a lipid coating that insulates the axon. The axon terminal
myelin c overing of axons in the PNS is formed by neuroglial cells
called Schwann cells or neurolemmocytes. Oligodendrocytes, an- direction
other type of neuroglial cell, perform a similar function in the of conduction
CNS. Because myelin is contained in cells, the cell’s metabolism
can influence the amount and composition of myelin. Gaps in the
myelin sheath are called nodes of Ranvier (neurofibril nodes). Figure 8.2 Neuron anatomy. (a) Sensory neuron with
dendritelike structures projecting from the peripheral end of the
These gaps greatly increase the speed of conduction for a nerve
axon. (b) Interneuron (from the cortex of the cerebellum) with
signal, as you’ll discover shortly. highly branched dendrites. Note that the myelin sheath is absent.
(c) Motor neuron. Note the branched dendrites and the single,
Types of Neurons long axon, which branches only near its tip.
Neurons can be classified according to their function and structure.
Sensory neurons take nerve signals from sensory receptors to structure that is termed unipolar (Fig. 8.2a). In unipolar neurons,
the CNS. The sensory receptor, which is the distal end of the the extension from the cell body divides into a branch that comes
long axon of a s ensory neuron, may be as simple as a naked nerve to the periphery and another that goes to the CNS. Because both
ending (a pain receptor), or it may be a part of a highly complex branches are long and transmit nerve signals, it’s now generally
organ, such as the eye or ear. Almost all sensory neurons have a accepted to refer to them collectively as an axon.
Resting Potential
Anyone who has ever used a battery has employed an energy source Action Potential
that’s manufactured by separating positively charged ions across a The resting potential energy of the neuron can be used to perform
membrane from negative ions. The battery’s potential energy can the work of the neuron: conduction of nerve signals. The process
be used to perform work: lighting a flashlight, for example. When a of conduction is termed an action potential, and it occurs in the
neuron is resting, it too possesses potential energy, much like a fully axons of neurons. An action potential begins with a stimulus,
charged battery. This energy, called the resting potential, exists be- which activates the neuron. (For example, poking the skin with a
cause the cell membrane is polarized: positively charged in the space sharp pin would be a stimulus for pain neurons in the skin.) The
immediately outside the cell membrane, and negatively charged in a stimulus affects specific protein channels, called voltage-regulated
small area just inside the cell membrane. The cell’s outside perim- sodium gates. These sodium gates are different from sodium chan-
eter is positive because positively charged sodium (Na1) ions cluster nels because they are not constantly open; rather, voltage changes
around the cell. There is a concentration gradient for sodium ions, cause them to open and close. Once sodium gates have opened,
and the ions can diffuse into the cell through protein molecules called sodium ions rush into the cell. Adding positively charged sodium
sodium channels. (A cell channel is like a door that remains open all ions causes the inside of the axon to become positive, compared to
the time.) However, the cell membrane is relatively impermeable to the outside (Fig. 8.3b).
sodium ion diffusion when the cell is at resting potential. In addition, If sufficient numbers of sodium ions pass into the cell, the
positively charged potassium ions are concentrated just inside the cell’s voltage will reach a new, higher voltage, called the cell’s
perimeter of the cell membrane, and the cell membrane is perme- threshold. Once this voltage is reached, increasing numbers of
able to potassium. Because of this concentration gradient, potassium voltage-regulated sodium gates will open and the cell potential
ions are constantly diffusing out of the cell, through their own set will abruptly rise. The resulting change is called depolarization.
of protein channels. There, these ions contribute to the extracellular Depolarization continues until the intracelluar voltage reaches a
positive charge. The inside of the cell is negatively charged because of value of approximately 135 mV.
the presence of large, negatively charged proteins and other molecules Once the change in voltage is complete, the voltage-regulated
that are trapped inside the cell because of their large size. sodium gates close and a separate set of voltage-regulated potas-
It’s important to note, though, that the charged areas on either sium gates opens. Potassium rapidly leaves the cell (Fig. 8.3c). As
side of the cell membrane that are responsible for creating the rest- positively charged potassium ions exit the cell, the inside of the cell
ing potential are very small. Most of the intracellular and extracel- becomes negative again (due to the presence of large, negatively
lular fluid is electrically neutral—the positive and negative charges charged ions trapped inside the cell). This change in polarity is
are perfectly balanced. called repolarization (Fig. 8.3d). Once the action potential is com-
Like a battery, the neuron’s resting potential energy can be plete, the sodium and potassium ions are rapidly restored to their
measured in volts. A D-size flashlight battery has 1.5 volts; a proper place through the action of the sodium-potassium pump.
2 1
intracellular extracellular
(recording) (reference)
microelectrode electrode
K+
K + channel
Na+
Na+ K+
channel gate
Na+
gate
35 35
0 0
mV
mV
a Na+ and K+ gates closed b Na+ gates open, Na +
–70 enters cell –70
Resting membrane Depolarization
potential
a. b.
35 35
0 0
mV
mV
Figure 8.3 Resting potential and action potential in an unmyelinated axon. (a) Resting potential. Sodium ions (red dots)
are concentrated outside the cell; potassium (blue dots) and large anions are inside the cell. Potential is approximately 70 mV; the in-
side of the cell is negative compared to the outside. (b) Action potential: depolarization. Na1 gates open and sodium ions flow into
cell; the inside of the cell becomes positive. (c) Action potential: repolarization. K1 gates open and potassium ions flow out. (d) Repo-
larization: Both Na1 and K1 gates are closed. When the sodium-potassium pump restores the ions to their places, repolarization is
complete.
a.
+ + + + + + + + + + + + + – – – + +
– – – – – – – – – – – – –+ + + – – –
– – – – – – – – – – – – –+ + + – – –
+ + + + + + + + + + + + +– – – + +
action
potential
repolarization depolarization
b.
Figure 8.4 Conduction of an action potential in unmyelinated and myelinated axons. (a) In an unmyelinated axon, con-
duction is slow. (b) In a myelinated axon, the action potential quickly travels from one node of Ranvier to the next, and the speed
of conduction is much more rapid. Almost all axons are myelinated in humans.
Once a neurotransmitter has been released into a synaptic molecular breakdown. The short existence of neurotransmitters at a
cleft and has initiated a response, it is removed from the cleft. In synapse prevents continuous stimulation (or inhibition) of postsyn-
some synapses, the postsynaptic membrane contains enzymes that aptic membranes.
rapidly inactivate the neurotransmitter. For example, the enzyme The What’s New feature, Research on Alzheimer Disease,
acetylcholinesterase (AChE) breaks down acetylcholine. In other discusses the disease, which is due in part to a lack of ACh in
synapses, the presynaptic membrane rapidly reabsorbs the neu- the brain. It is also of interest to note that many available drugs
rotransmitters, possibly for repackaging in synaptic vesicles or for enhance or block the release of a neurotransmitter, mimic the
Presynaptic neuron
arriving action
potential 1. After an action
potential arrives
at an axon
axon of terminal (arrow),
presynaptic Ca2+ enters,
(sending) and synaptic
Ca2+ vesicles fuse
neuron
with the plasma
membrane of
axon branches of the presynaptic
sending neurons dendrite neuron.
axo
axon
term
terminal Synaptic vesicles
enclose neuro-
transmitter.
Synapse
a. Presynaptic membrane
postsynaptic
inhibitory (receiving) Postsynaptic Synaptic
synapse neuron neuron cleft
excitatory
synapse 2. Neuro-
transmitter
molecules
axon cell body are released
terminals and bind to
receptors
axon
on the
membrane
of the
postsynaptic
neuron. Postsynaptic
neuron
neurotransmitter
3. When an
excitatory
neuro- neuro-
transmitter transmitter
binds to a
receptor,
receptor Na+ diffuses
ion gate into the
Na+ postsynaptic
neuron.
Postsynaptic
neuron
Figure 8.5 Synapse structure and function. (a) A single nerve cell body may have many excitatory synapses (green) as
well as inhibitory synapses (red). (b) Photomicrograph of a nerve cell body, showing multiple axon terminals that form s ynapses.
(c) The sending neuron is called the presynaptic neuron, and the receiving neuron is the postsynaptic neuron. (d) Transmission
across a synapse from one neuron to another occurs when a neurotransmitter is released at the presynaptic membrane, diffuses
across a synaptic cleft, and binds to the receptors on the gates found in the postsynaptic membrane. Because the gates shown in
the illustration are Na1 gates, the synapse is excitatory.
Alzheimer disease (AD) is an irreversible, fatal disorder characterized Alzheimer cell protein is another possible avenue for research. At this
by a gradual loss of reason that begins with memory lapses and ends with time, only five drugs are accepted for disease treatment. One category,
the inability to perform any activities. Personality changes such agitation cholinesterase inhibitors (Aricept®, Razadyne®, Exelon®, Reminyl®),
and hostility, and memory deficits that affect daily routines often signal works at neuron synapses in the brain, slowing the activity of the enzyme
the onset of AD. For example, a normal 60- to 70-year-old might forget that breaks down acetylcholine (ACh). Allowing ACh to accumulate in
the name of a friend not seen for years, but someone with AD forgets the synapses keeps memory pathways in the brain functional for a longer
name of a neighbor who visits daily. Likewise, a healthy senior might period of time. The newest drug, memantine (Namenda®), blocks excito-
forget where he placed his car keys, while a person with AD will forget toxicity: the tendency of diseased neurons to self-destruct. This medica-
what those keys are for. People afflicted with AD become confused and tion is used only in moderately to severely affected patients. Using the
tend to repeat the same question. Signs of mental disturbance eventually drug allows neurons involved in memory pathways to survive longer in
appear, and patients gradually become bedridden and die of a complica- affected patients. However, it’s important to note that neither category of
tion, such as pneumonia. At the cellular level, AD is characterized by the medication cures AD. Both merely slow the progress of disease symp-
presence of abnormally structured neurons and a reduced amount of the toms, allowing the patient to function independently for a longer period
neurotransmitter acetylcholine (see pp. 167–168). These defective neu- of time. Additional research is currently underway to test the effective-
rons are especially seen in the portions of the brain involved in reason and ness of anticholesterol statin drugs, as well as anti-inflammatory medica-
memory. The AD neuron has two pathological features. The first consists tions, in slowing the progress of the disease.
of bundles of fibrous protein, called neurofibrillary tangles, which sur-
Research on Prevention
round the nucleus in the cells. The tangles are due to an abnormal form of
tau, a protein molecule that normally helps to stabilize microtubules that Much of current research on AD focuses on prevention. Early findings
form the cell’s cytoskeleton. In addition to these tangles, protein-rich have shown that risk factors for cardiovascular disease—heart attacks and
accumulations, called amyloid plaques, envelop the axon branches. Over stroke—also contribute to an increased incidence of AD. These include
time, affected neurons will die. The cortex and hippocampus shrivel, the elevated blood cholesterol and blood pressure, smoking, obesity, seden-
brain shrinks in volume, and the ventricles become enlarged. tary lifestyle, and diabetes mellitus (see Chapter 12). Low-level infection
caused by gum disease has also been shown to increase the probability of
Research Regarding Its Causes developing heart disease, and by extension, Alzheimer disease. Thus,
As techniques for genetic study continue to improve, several genetic muta- evidence suggests that a lifestyle tailored for good cardiovascular health
tions specific to Alzheimer have been identified. One set, designated by may also prevent AD. Slight changes in diet may also lessen the threat of
the acronyms APP, PS1, and PS2, are termed deterministic. People who developing AD: boosting vitamins B and D, eating fatty fish such as
inherit one of these three mutated genes will always develop the disease, salmon, and drinking coffee. Further, younger people must try to prevent
called autosomal dominant Alzheimer disease (ADAD). It’s interesting to blows to the head. It’s been shown that head injuries (such as those expe-
note that APP, the first of these defective genes to be discovered, is found rienced by football players) can increase the risk of developing AD in
on chromosome 21. Down syndrome results from the inheritance of three later life 19-fold. Wearing seat belts and helmets and taking steps to pre-
copies of chromosome 21, and people with Down syndrome tend to vent falls are commonsense, easy ways to prevent head injury. Finally,
develop AD. (You will learn more about autosomal dominant disorders in staying mentally, physically, and socially active—as long as possible—
Chapter 19.) Mutation of a fourth gene, designated APO, puts patients at will help to slow the course of mental impairment for AD sufferers.
risk but does not always result in disease. Scientists are now studying vic-
tims with mutations to try to discover the exact cause for the disease. Early Detection and Hope for a Cure
Recent findings have led researchers to believe that the neuron deteriora- Currently, researchers are testing vaccines for AD that would target the
tion seen in Alzheimer disease patients may be caused by the spread of the patient’s immune system to destroy amyloid protein. Early study results
tau protein from one cell to the next, much as a virus is spread from one show some promising outcomes of this treatment in early-stage patients.
infected cell to another. Other studies have implicated a second protein, However, scientists believe that curing AD will require an early diagnosis
striatal-enriched tyrosine phosphatase, or STEP, in the cell destruction because it’s thought that the disease may begin in the brain 15 to 20 years
found in Alzheimer sufferers. Further, other investigators are exploring the before symptoms ever develop. At present, diagnosis can’t be made with
role of cell lysosomes in AD, suspecting that these essential organelles absolute certainty until the brain is examined at autopsy. In the future,
may be failing to destroy the abnormal proteins found in diseased cells. cerebrospinal fluid testing may allow amyloid proteins to be detected
before disease symptoms appear. Researchers are also developing ways
Research into Its Treatment to tag the amyloid protein with radioactive molecules, which will allow
Each new finding about what causes Alzheimer disease creates new pos- detection of the protein using a PET scan. (You learned about PET and
sibilities for its treatment as well. Researchers are now conducting clini- other imaging techniques in Chapter 1.) The Medical Focus reading in
cal testing on antibodies that block cell-to-cell transmission of the tau Chapter 9 describes an eye scan technique that might allow an earlier
protein. (You can read more about antibodies in Chapter 13.) A second diagnosis, and the What’s New reading on page 178 describes an
treatment might involve the creation of drugs that block formation of the exciting breakthrough in cell culture that will create new options for
STEP protein. Boosting lysosomal degradation of the abnormal studying neurons and drug therapies in the laboratory.
cerebellum
vertebra
intervertebral
foramen
spinal cord skin of scalp
meninges hypodermis
spinal nerve bone of skull
a.
dura mater
dural venous
arachnoid meninges
sinus
mater
a.
posterior (dorsal)
root intervertebral
posterior root foramen
ganglion
spinal epidural
nerve space
posterior
anterior vertebra (dorsal) root
(ventral) root branches
b. posterior
(dorsal) root
central canal gray matter ganglion
posterior
posterior root white matter
posterior root intervertebral
ganglion foramen
anterior
spinal
nerve cut vertebrae
anterior root
meninges
c. d.
The Brain
Structure of the Spinal Cord The human brain consists of four major structures: the cerebrum,
Figure 8.7b shows how an individual vertebra protects the spinal the diencephalon, the cerebellum, and the brain stem. The brain’s
cord. The spinal nerves extend from the cord between the verte- four ventricles can be found within these brain structures. The
brae. Intervertebral disks, which are composed of tough fibrocarti- paired lateral ventricles are enclosed by the cerebrum, the third
lage and filled with gelatinous material, separate each vertebra. If a ventricle lies in the center of the diencephalon, and the fourth ven-
disk is torn open, this herniated disk may compress spinal nerves, tricle travels within the brain stem, just anterior to the cerebellum
causing pain and loss of function. (Fig. 8.8a).
A cross section of the spinal cord shows a central canal, gray The electrical activity of the brain can be recorded in the form
matter, and white matter (Fig. 8.7a,b,c). Both the central canal of an electroencephalogram (EEG). Electrodes are taped to dif-
and the subarachnoid space (between the dura mater and arach- ferent parts of the scalp, and an instrument records the so-called
noid mater that cover the spinal cord) contain cerebrospinal fluid. brain waves. The EEG is a diagnostic tool; for example, an ir-
The gray matter is centrally located and shaped like the letter H. regular pattern can signify epilepsy or a brain tumor. Absence of
Portions of sensory neurons and motor neurons are found there, electrical activity on an EEG signifies brain death.
as are interneurons that communicate with these two types of
neurons. The posterior (dorsal) root of a spinal nerve contains
sensory fibers entering the gray matter, and the cell bodies of The Cerebrum
these sensory nerves can be found in an enlarged area called the Let’s begin our study of the brain with the cerebrum, the largest
posterior root ganglion. The anterior (ventral) root of a spinal portion of the brain in humans. The cerebrum is the last center to
nerve contains motor fibers exiting the gray matter. The posterior receive sensory input and carry out integration before commanding
and anterior roots join, forming a spinal nerve that leaves the ver- voluntary motor responses. It communicates with and coordinates
tebral canal through the intervertebral foramen. Spinal nerves are the activities of the other parts of the brain. The cerebrum carries
a part of the PNS. out the higher thought processes required for learning and memory
The white matter of the spinal cord contains ascending tracts, and for language and speech.
which take sensory information to the spinal cord and brain, and The cerebrum has two halves called the left and right cerebral
descending tracts, which take motor information from the brain. hemispheres (Fig. 8.9). A lateral ventricle can be found inside each
Ascending tracts are generally located in the posterior white hemisphere. A deep groove, the longitudinal fissure, separates the left
matter; descending tracts are found in the anterior white matter. and right cerebral hemispheres. Still, the two cerebral hemispheres are
Because the tracts typically cross just after they enter and exit the connected by a bridge of white matter called the corpus callosum.
brain, the left brain controls the right side of the body and the right Ridges called gyri are separated by shallow grooves called
brain controls the left side of the body. sulci (sing., sulcus). Specific sulci divide each hemisphere into
lobes (Fig. 8.9). Note that each lobe of the brain is located underneath
the skull bone that shares its name. The frontal lobe lies under the
Functions of the Spinal Cord
frontal bone, anterior to the parietal lobe and bone. The occipital
The spinal cord provides a means of communication between the lobe is deep to the occipital bone, in the posterior area of the cra-
brain and the peripheral nerves that leave the cord. nial vault. The temporal lobe is the lateral portion of the cerebral
When someone touches your hand, sensory receptors gener- hemisphere. A fifth, very small lobe called the insula (not shown)
ate action potentials that travel by way of sensory nerve axons to lies directly deep to the lateral sulcus. Its function continues to be
the spinal cord. One of several ascending tracts next carries the researched, but it’s thought to be involved in speech processing,
information to the sensory area of the brain. When you voluntarily the sense of taste, and determining social emotions (such as em-
move your limbs, action potentials originating in the motor control barrassment, resentment, empathy, and self-confidence).
area of the brain pass down one of several descending tracts to the The cerebral cortex is a thin but highly convoluted outer layer
spinal cord and out to your muscles by way of motor nerve axons. of gray matter that covers the cerebral hemispheres. The cerebral
The What’s New on page 178 discusses promising new therapies cortex contains over one billion cell bodies and is the region of the
for patients whose spinal cord is injured. brain that accounts for sensation, voluntary movement, and all the
We’ll see that the spinal cord is also the center for thousands thought processes we associate with consciousness.
of reflex arcs (see Fig. 8.13): A stimulus causes sensory receptors
to generate action potentials that travel in sensory neurons to the
spinal cord. Interneurons integrate the incoming data and relay Motor and Sensory Areas of the Cortex
signals to motor neurons. A response to the stimulus occurs when The primary motor area is in the frontal lobe just anterior to the
motor axons cause skeletal muscles to contract. Each interneu- central sulcus (Fig. 8.9). Voluntary commands to skeletal mus-
ron in the spinal cord has synapses with many other neurons, and cles begin in the primary motor area, and each part of the body
Cerebrum
skull
meninges
corpus
callosum
choroid
plexus
Diencephalon
thalamus
(in sides and roof of
third ventricle)
hypothalamus
pituitary gland
Brain stem
Cerebellum
midbrain
pons
fourth ventricle
medulla
oblongata spinal cord
a. Parts of brain
lateral
ventricles
third
ventricle
fourth
ventricle
spinal
cord
b. c.
Figure 8.8 The human brain. (a) The cerebrum, seen here in sagittal section, is the largest part of the brain in humans.
(b) Ventricles of the brain in a lateral view. Ventricles are hollow cavities filled with cerebrospinal fluid. (c) Frontal view of the brain’s
four ventricles.
is controlled by a certain section (Fig. 8.10a). The right primary motor cortex in the brain dedicated to them. Similarly, the face
motor area controls the left side of the body and vice versa. and hands are among the most sensitive areas of the body, and
The primary somatosensory area is just posterior to the the large area of the sensory cortex receiving information from
central sulcus in the parietal lobe. Sensory information from them corresponds to that fact. As with the brain’s motor areas, the
the skin and skeletal muscles arrives here, where each part of left hemisphere’s s omatosensory area receives information from
the body is sequentially represented (Fig. 8.10b). As you study the right side of the body, and vice versa.
Figure 8.10, notice that the areas of the body with the greatest A primary taste area, located within adjacent areas of the parietal
voluntary c ontrol—the face and hands—have the largest area of lobe and insula, accounts for taste sensations. A primary visual area in
Occipital lobe
primary
olfactory primary
area visual area
lateral sulcus visual
association
Temporal lobe area
auditory association area
primary auditory area
sensory speech (Wernicke’s) area
a.
the occipital lobe receives information from our eyes, and a primary omentary lack of oxygen during birth can damage the motor areas of
m
auditory area in the temporal lobe receives information from our ears. the cerebral cortex so that cerebral palsy, a condition characterized
by a spastic weakness of the upper and lower limbs, develops.
The somatosensory association area, located just posterior to the
Begin Thinking Clinically primary somatosensory area, processes and analyzes sensory informa-
tion from the skin and muscles. The visual association area associates
Suppose that a woman slips on ice in the winter and falls
new visual information with memories of previously received visual
backward, striking the back of her head on the pavement.
information. It might “decide,” for example, whether or not we have
The accident results in a concussion to the woman’s occip-
previously seen a particular face, symbol, or other o bject. The auditory
ital lobe. Which sense might be affected?
association area performs the same functions with regard to sounds.
Answer and discussion in Appendix A.
Processing Centers
There are a few areas of the cortex that receive information from
Association Areas the other association areas and perform higher-level analytical
Association areas are places where sensory signals are integrated and functions. The prefrontal area, a processing area in the frontal
interpreted, and where memories are stored. Anterior to the primary lobe, receives information from the other association area and
motor area is a premotor area. The premotor area organizes motor func- uses this information to reason and plan our actions. Integration in
tions for skilled motor activities, and then the primary motor area sends this area accounts for our most cherished human abilities to think
signals to the cerebellum and the basal nuclei, which integrate them. A critically and to formulate appropriate behaviors.
Figure 8.10 Portions of the body controlled by the primary motor area and the primary somatosensory area of the cerebrum. Notice
that the size of the body part in the diagram reflects the amount of cerebral cortex devoted to that body part.
The unique ability of humans to speak is partially dependent These so-called basal nuclei (formerly termed basal ganglia) in-
upon the motor speech area, also called Broca’s area, a process- tegrate motor commands, ensuring that proper muscle groups are
ing area usually located in the left frontal lobe. Signals originating activated or inhibited. Huntington disease and Parkinson’s dis-
here pass to the premotor area before reaching the primary motor ease, which are both characterized by uncontrollable movements,
area. Damage to this area can interfere with a person’s ability to are believed to be due to an imbalance of neurotransmitters in the
coordinate the respiratory and oral movements that produce speech. basal nuclei.
Wernicke’s area, also called the general interpretive area,
receives information from all of the other sensory association The Diencephalon
areas. Like Broca’s area, Wernicke’s area is usually located in
the brain’s left hemisphere. Its role involves recognizing and un- The hypothalamus and the thalamus are both in the diencephalon,
derstanding spoken and written language. Damage to this area a region that encases the third ventricle (see Fig. 8.8a). The
interferes with a person’s ability to interpret written and spoken hypothalamus forms the floor of the third ventricle. The hypo-
messages, even though the spoken words may be a part of the thalamus is an integrating center that helps maintain homeostasis
person’s vocabulary. Wernicke’s area and Broca’s area cooperate by regulating hunger, sleep, thirst, body temperature, and water
to allow human communication. balance. The hypothalamus produces the hormones secreted by
the posterior pituitary gland and secretes hormones that control the
anterior pituitary. Therefore, it is a link between the nervous and
Central White Matter
endocrine systems.
Much of the rest of the cerebrum beneath the cerebral cortex is com- The thalamus consists of two masses of gray matter located
posed of white matter. Tracts within the cerebrum take information in the sides and roof of the third ventricle. The thalamus is on
between the different sensory, motor, and association areas pictured the receiving end for all sensory input except smell; it functions
in Figure 8.9. The corpus callosum, previously mentioned, contains as a sensory “relay center.” Visual, auditory, and somatosensory
tracts that join the two cerebral hemispheres. Descending tracts from information arrive at the thalamus via the cranial nerves and
the primary motor area communicate with various parts of the brain tracts from the spinal cord. The thalamus integrates this infor-
and transmit instructions to the opposite side of the brain stem and mation and sends it on to the appropriate portions of the cere-
spinal cord. Ascending tracts from lower brain centers send sensory brum. The thalamus is involved in arousal of the cerebrum, and
information up to the primary somatosensory area (Fig. 8.10). it also participates in higher mental functions such as memory
and emotions.
Basal Nuclei The pineal gland (sometimes referred to as the pineal body),
While the bulk of the cerebrum is composed of tracts, there which secretes the hormone melatonin and regulates our body’s
are masses of gray matter located deep within the white matter. daily rhythms, is located in the posterior diencephalon.
As you know from page 170, Alzheimer disease results from a Recently, researchers successfully developed a technique for
complex biochemical process in neurons. Two proteins—the amy- creating a human study model. First, neural stem cells were geneti-
loid that causes plaques to form between neuron synapses, and the cally engineered to be immortal in cell culture (like the HeLa cells
tau that causes neurofibrils to tangle—are known to be involved in described in the Chapter 4 opening reading). Next, these cells were
the disease process. However, hundreds of questions about the pro- successfully grown in a gel medium, where they formed three-
cess remain. Why do some people form the proteins, but show no dimensional neural networks, much like those of a human brain.
signs of disease? Does plaque formation cause tangle formation? Researchers then induced the same gene mutations found in auto-
Do the proteins themselves cause the disease symptoms, or do they somal dominant Alzheimer disease (ADAD). For the first time, the
result when the immune system destroys damaged cells? Why do neurons grown in these cell cultures formed complex networks
specific mutations always doom some people to die from the dis- that showed the two distinct pathological changes of Alzheimer
ease? Why does disease risk increase with age? To date, research disease: first, amyloid plaques and then the resulting neurofibril-
into these and other questions has used mice equipped with human lary tangles. Thus, this cell culture technique has created a power-
Alzheimer genes as the mammalian study model. However, this ful new research tool: a working reproduction of an “Alzheimer
type of study has had serious limitations. Obviously, mice aren’t brain” in a petri dish. Scientists hope that having this replica will
humans. The animal brains grow amyloid plaques, but not the allow possible drugs for Alzheimer disease to be rapidly tested. In
resulting neurofibrillary tangles seen in human brains. Further, addition, this 3-D neural network “brain” could also be used to
experimental drugs that cured mice failed to show any benefits in investigate other neurodegenerative disorders such as Parkinson’s
humans. disease.
Limbic System Stimulation of different areas of the limbic system causes the
subject to experience rage, pain, pleasure, or sorrow. By causing
The limbic system (illustrated in purple in the following figure)
pleasant or unpleasant feelings about experiences, the limbic sys-
is a collection of structures from both the cerebrum and the dien-
tem apparently guides the individual into behavior that is likely to
cephalon. It lies just inferior to the cerebral cortex and contains
increase the chance of survival.
neural pathways that connect portions of the cerebral cortex and
The limbic system is also involved in learning and memory.
the temporal lobes with the thalamus and the hypothalamus:
In particular, the most inferior structure of the limbic system,
the hippocampus, is vital in processing of short-term memory
to become long-term memory. Learning requires memory, and
memory is stored in the sensory regions of the cerebrum, but
thalamus just what permits memory development is not definitely known.
The involvement of the limbic system in memory explains why
emotionally charged events result in our most vivid memories.
The fact that the limbic system communicates with the sen-
sory areas for touch, smell, vision, and so forth accounts for the
hypothalamus ability of any particular sensory stimulus to awaken a complex
olfactory bulb memory.
and tract
amygdala
The Cerebellum
hippocampus The cerebellum is separated from the brain stem by the
fourth ventricle (see Fig. 8.8a). The cerebellum has two
hemispheres, which are joined by a narrow median portion.
Each portion is primarily composed of white matter, which
in longitudinal section has a treelike pattern. Overlying the
Olfactory (I) Sensory I: Mucous membrane of nose to Olfactory receptors for sense of smell
olfactory bulbs
Optic (II) Sensory II: Retina → optic nerve → thalamus → Retina for sense of sight
occipital lobe
Oculomotor (III) Motor III: Midbrain → eye and eyelid Eye muscles (including eyelids and lens); pupil
(parasympathetic division)
Trochlear (IV) Motor IV: Midbrain → eye Eye muscles
Sensory V: Sensory: Teeth, eyes, skin, and tongue
Trigeminal (V) Teeth, eye, skin,
Mixed
tongue → pons
Motor Motor: Jaw muscles (chewing)
Pons → jaw muscles
Abducens (VI) Motor VI: Pons → eye Eye muscles
Sensory VII: Sensory: Taste buds of anterior tongue
Facial (VII) Tongue → pons
Mixed
Motor Motor: Facial muscles (facial expression) and glands
Pons → facial muscles, (tear and salivary)
salivary glands, tear glands
Vestibulocochlear (VIII) Sensory VIII: Inner ear → pons and medulla Inner ear for sense of balance and hearing
(also called auditory;
acoustic) Sensory IX: Sensory: Pharynx
Glossopharyngeal (IX) Mixed Tongue, throat → pons
Motor Motor: Pharyngeal muscles (swallowing), salivary
Pons → salivary gland, glands
throat muscles
Sensory X: Sensory: Internal organs, external ear canal,
Vagus (X) Eardrum, ear canal, throat, heart, eardrum, back of throat
Mixed lungs, abdominal organs → medulla
Motor Motor: Internal organs (parasympathetic division),
Medulla → throat and larynx, heart, throat muscles (somatic motor division)
lungs, abdominal organs
Spinal accessory (XI) Motor XI: Medulla → muscles of throat, neck, Neck and back muscles
shoulder
Hypoglossal (XII) Motor XII: Medulla → tongue muscles Tongue muscles
cervical, thoracic, lumbar, sacral, or coccygeal regions of the verte- Somatic Motor Nervous System and Reflexes
bral column. The first spinal nerve, C1, emerges between the skull
Most actions in the somatic motor nervous system are volun-
and the atlas (the first cervical vertebra). The remaining spinal
tary. These actions, such as when we decide to move a limb,
nerves are designated according to their location in relation to the
always originate in the motor cortex. You will remember that
vertebrae because each passes through an intervertebral foramen as
the motor cortex is in the posterior part of the frontal lobe.
it leaves the spinal cord. This organizational principle is illustrated
Other actions in the somatic m otor nervous system are due to
in Figure 8.12.
reflexes—automatic involuntary responses to changes occur-
All spinal nerves are mixed nerves because they contain both
ring inside or outside the body. A reflex occurs quickly; we
sensory fibers that conduct signals to the spinal cord from sensory
don’t even have to think about it. Reflexes are protective mecha-
receptors and motor fibers that conduct signals away from the cord
nisms that are essential to homeostasis. They keep the internal
to effectors. The sensory fibers enter the cord via the posterior
organs functioning within normal bounds and protect the body
root, and the motor fibers exit by way of the anterior root. As you’ll
from external harm.
recall (from section 8.2), the cell body of a sensory neuron is found
Some reflexes, called cranial reflexes, involve the brain, as
in the posterior root ganglion (see Figs. 8.7 and 8.13). Each spinal
when we automatically blink our eyes when an object nears the
nerve serves the particular region of the body in which it is located
eye suddenly. Figure 8.13 illustrates the path of a reflex within the
(Table 8.2).
PNS
artery
spinal and vein
nerves
Cranial Nerves
Figure 8.11 Cranial and spinal nerves. (a) A single nerve is composed of the axons of many neuron fibers, arranged in
bundles called fascicles. Axons are covered by endoneurium; fascicles are covered by perineurium, and the nerve is enclosed in
epineurium. (b) Cross section scanning electron micrograph of a fascicle containing both myelinated axons (surrounded by gold
myelin sheath) and unmyelinated axons. Endoneurium (tan tissue) surrounds each axon. (c) Inferior surface of the brain showing the
attachment of the 12 pairs of cranial nerves.
L5
Autonomic Motor Nervous System
and Visceral Reflexes
S1
The autonomic motor nervous system (ANS) is composed of the
S2 5 pairs of
sacral nerves
sympathetic and parasympathetic divisions (Fig. 8.14). These two
S3
S4
divisions have several features in common: (1) They function au-
tomatically, with little or no voluntary control; (2) all internal
S5
1 pair of coccygeal organs have fibers from either or both divisions; and (3) they uti-
Co1
nerves lize two motor neurons and one ganglion to transmit an action
potential. (By contrast, a somatic motor neuron travels directly
to its effector, without synapsing at a ganglion.) The first neuron
has a cell body within the CNS and a preganglionic axon fiber
Figure 8.12 Spinal nerves. The number and kinds (the term preganglionic indicates that the axon travels to the gan-
of spinal nerves are shown here. Table 8.2 lists the functions glion). The second neuron has a cell body within the ganglion
of some of the major spinal nerves.
and a postganglionic axon fiber (the axon travels away from the
ganglion to the effector).
Visceral reflex actions, such as those that regulate blood
pressure and breathing rate, are especially important to main-
somatic motor nervous system that involves only the spinal cord tenance of homeostasis. These reflexes begin when the sen-
(called a spinal reflex). If the skin on your hand is poked with a sory neurons in contact with internal organs send messages
sharp pin, a pain sensory receptor in the skin generates action po- via spinal nerves to the CNS. They are completed when
tentials that move along a sensory fiber through the posterior root motor neurons within the autonomic system stimulate smooth
ganglia toward the spinal cord. Sensory neurons enter the cord muscle, c ardiac muscle, or a gland. These structures are also
posteriorly and form synapses with many interneurons. Some of effectors.
posterior (dorsal)
root ganglion central canal
white matter
Posterior
sensory gray matter
(Dorsal)
receptor
(in skin)
anterior
(ventral) root cell body of
motor neuron
Anterior (Ventral)
Figure 8.13 A reflex arc showing the path of a spinal reflex. A stimulus (e.g., a pinprick to the skin of the hand) causes sen-
sory receptors in the skin to generate nerve signals that travel in sensory axons to the spinal cord. Interneurons integrate data from sen-
sory neurons and then relay signals to motor neurons. Motor axons convey nerve signals from the spinal cord to a skeletal muscle, which
contracts. Movement of the hand away from the pin is the response to the stimulus.
Sympathetic Division: “Fight or Flight” (NE). The structure of NE is like that of epinephrine (adrena-
line), an adrenal medulla hormone that usually increases heart
The preganglionic fibers of the sympathetic division arise from
rate and contractility.
the middle, or thoracic-lumbar, portion of the spinal cord and
almost immediately terminate in ganglia that lie near the cord.
Therefore, in this division, the preganglionic fiber is short, but the
Parasympathetic Division:
postganglionic fiber that makes contact with an effector is long “Rest and Digest”
(Fig. 8.15a). The parasympathetic division includes several cranial nerves
The sympathetic division is especially important dur- whose preganglionic neurons are located in the brain stem
ing emergency situations when a person might be required to (e.g., the vagus nerve) as well as fibers that arise from the
fight or run away. It accelerates the heartbeat and dilates the sacral (inferior) portion of the spinal cord. Therefore, this
bronchi—active muscles, after all, require a ready supply of glu- division is often referred to as the craniosacral portion of
cose and oxygen. On the other hand, the sympathetic division the autonomic system. In the parasympathetic division, the
inhibits the digestive tract functions—digestion is not an im- preganglionic fiber (axon) is long, and the postganglionic
mediate necessity if you’re under attack. The neurotransmitter fiber (axon) is short because the ganglia lie near or within the
released by the postganglionic axon is primarily norepinephrine effector (Fig. 8.15b.)
slows heart
speeds
heart
dilates air
constricts
passages vagus nerve
bronchioles
thoracic
inhibits activity
nerves increases
of kidneys,
stomach, and intestinal
pancreas activity
decreases
intestinal activity
lumbar
nerves
ganglion
inhibits stimulates sacral
urination urination nerves
causes
orgasmic causes
contractions erection Acetylcholine is neurotransmitter.
sympathetic ganglia of genitals Norepinephrine is neurotransmitter.
Figure 8.14 Autonomic system structure and function. Sympathetic preganglionic fibers (left) arise from the thoracic and
lumbar portions of the spinal cord; parasympathetic preganglionic fibers (right) arise from the cranial and sacral portions of the spinal
cord. Most of the effectors are innervated by both divisions of the ANS (as shown). Where this is the case, the two divisions usually have
opposite effects.
norepinephrine
speeds acetylcholine
heart slows heart
short
postganglionic
vagus nerve
long
cervical preganglionic
nerves long
postganglionic
sympathetic
thoracic ganglion
nerves
short
preganglionic
a. b.
Figure 8.15 Sympathetic and parasympathetic pathways. (a) Because sympathetic ganglia usually lie close to the spinal
cord, the preganglionic neuron is short and the postganglionic neuron is long. (b) Parasympathetic ganglia are close to their target or-
gans, so the preganglionic neuron is long and the postganglionic neuron is short.
Sympathetic Parasympathetic
The illustration in Human Systems Work Together on page 188 Content CHECK-UP!
shows how the nervous system works with other systems in the
body to maintain homeostasis. The nervous system detects, inter- 15. A patient whose stroke caused loss of function to his upper
prets, and responds to changes in internal and external conditions limb developed decreased bone density in the limb. Why did
to keep the internal environment relatively constant. The hypo- this occur?
thalamus, an important nervous system structure, is also the master Answer in Appendix A.
controller for most of the endocrine system. Together, these two
Respiratory centers in
Skeletal System brain regulate breathing
rate.
Receptors send sensory
input from bones and Lungs provide oxygen
brain for neurons and rid the
joints to brain.
body of carbon dioxide
Bones protect sense produced by neurons.
spinal cord
organs, brain, and spinal
cord; store Ca2+ for nerve
function.
Digestive System
“My body is completely out of control. That’s the hardest thing about symptoms completely for a few weeks to months. However, as the
this disease. Sometimes I can’t move at all, or I move so slowly that it disease progresses, patients need increasingly stronger medications in
takes forever just to cross the room. Next thing you know, I’m jerking higher dosages to relieve the symptoms. These stronger medications
around like a puppet.” produce undesirable side effects, such as dizziness, sleepiness, and
Your patient has just described the classic symptoms of memory loss.
Parkinson’s disease, a progressive central nervous system disorder. Implants of dopamine-producing cells have also been placed into
The Parkinson’s patient is usually a person age 60 or older. However, the brain. These implants have had low success rates in relieving symp-
the disease is seen increasingly in younger people as well. Actor toms. Research into this practice has largely been discontinued. (Because
Michael J. Fox was just 38 years old when he announced publicly in the cells are often obtained from human embryos, scientists have also
1999 that he suffers from Parkinson’s disease. raised ethical concerns about the source of the implanted cells.)
If the patient’s facial muscles are involved, his or her face may Increasingly, therapy for Parkinson’s disease involves directly
not be able to show emotion, resulting in a fixed, masklike appear- treating brain tissue. In deep-brain stimulation (DBS), a set of elec-
ance. Routine tasks such as dressing and bathing become very diffi- trodes is implanted into precise centers in the brain. The electrodes are
cult. The sufferer has an increased risk of falling and injuring himself connected to an electrical neurostimulator implanted into the chest
because balance and coordination are also affected. The disease takes near the clavicle, or collarbone. The neurostimulator delivers continu-
its toll on the patient psychologically; most suffer depression as their ous electrical signals into the patient’s brain, blocking the signals that
activities and independence become more and more limited. cause Parkinsonian movement. Once implanted, the stimulator can be
Parkinson’s disease is caused by destruction of specific areas of adjusted from outside the body to achieve maximum symptom relief.
the brain called the basal nuclei (see page 176). Researchers have Pallidotomy is performed on an awake patient. In this procedure, a
determined that these basal nuclei nerve cells produce the neurotrans- fine probe is placed into the brain tissue. Next, electrical signals are
mitter dopamine. The lack of this neurotransmitter seems to cause the applied to pinpoint the area for treatment, and the patient describes
signs and symptoms of the disorder. Treatment for the disease has, the signal’s effects to the surgeon. Based on these descriptions, the
until recently, focused on ways to replace dopamine in the brain. Drug surgeon can burn a tiny hole in the brain tissue, permanently stopping
treatment produces temporary dopamine replacement and r elieves the the signals that cause abnormal movements.
Summary
8.1. Nervous System while inhibitory neurotransmitters gray matter, has five lobes in
The nervous system permits sensory may prevent one. each hemisphere. The frontal
input, performs integration, and F. There are at least 100 known lobe initiates motor output. The
stimulates motor output. types of neurotransmitters. parietal lobe is the final receptor
A. The nervous system is divided 8.2. Central Nervous System for sensory input from the skin
into the central nervous system A. The CNS, consisting of the spinal and muscles. The other lobes re-
(brain and spinal cord) and the cord and brain, is protected by ceive specific sensory input.
peripheral nervous system (affer- the meninges and the cerebrospi- Various association areas in-
ent and efferent nervous sys- nal fluid. tegrate sensory data. Processing
tems). The CNS lies in the midline B. The spinal cord, located in the centers integrate data from other
of the body, and the PNS is lo- vertebral column, is composed of association areas: The prefrontal
cated peripherally to the CNS. white matter and gray matter. area carries out higher mental
B. Nervous tissue contains neurons C. White matter contains bundles of processes; Broca’s area and
and neuroglia. Each type of neu- nerve fibers, called tracts, which Wernicke’s area are concerned
ron (motor, sensory, and inter- conduct nerve signals to and with speech.
neuron) has three parts from the higher centers of the G. The diencephalon includes the
(dendrites, cell body, and axon). brain. Gray matter is mainly hypothalamus, thalamus, and pi-
Neuroglia support, protect, and made up of short fibers and cell neal gland. The hypothalamus
nourish the neurons. bodies. helps control the functioning of
C. All axons transmit the same type D. The spinal cord is a center for re- most internal organs and con-
of nerve signal: a change in po- flex action and allows communi- trols the secretions of the pitu-
larity (called an action potential) cation between the brain and the itary gland. The thalamus
that moves along the membrane peripheral nerves leaving the receives sensory impulses from
of a nerve fiber. Saltatory con- spinal cord. all parts of the body and relays
duction in myelinated axons is a E. The brain has four ventricles. them to the appropriate area of
faster type of conduction. The lateral ventricles are found the cerebrum.
D. Transmission of a nerve signal in the left and right cerebral H. The limbic system includes por-
across a synapse is dependent hemispheres. The third ventricle tions of the cerebrum, the thala-
on the release of a neurotrans- is found in the diencephalon. mus, and the hypothalamus. It is
mitter into a synaptic cleft. The fourth ventricle is found in involved in learning and memory
E. Graded potentials vary in size the brain stem. and in causing the emotions that
and can be excitatory or inhibi- F. The cerebrum is divided into the guide behavior.
tory. Excitatory neurotransmitters left and right hemispheres. The I. The cerebellum controls balance
may cause an action potential, cerebral cortex, a thin layer of and complex muscular movements.
Study Questions
1. What are the functions of the nervous well-known neurotransmitters. 10. Name the other parts of the brain, and
system? (p. 163) (pp. 167–169, 171) give a location and function for each
2. What are the two main divisions of the 6. Name the meninges, and describe part. (pp. 176, 178–180)
nervous system? How are these divi- their locations. Where do you find ce- 11. Describe the structure of a nerve. In
sions subdivided? (pp. 163–164) rebrospinal fluid? (pp. 171–172) general, discuss the location and func-
3. What is the general structure of a 7. Describe the structure and function of tion of the cranial nerves and the spi-
neuron, and what are the functions of the spinal cord. (pp. 172–173) nal nerves. (pp. 180–181)
three different types of neurons? 8. What is the difference between the 12. Describe a spinal reflex, including the
(pp. 164–165) cerebrum and the cerebral cortex? role played by a sensory nerve fiber,
4. Describe the resting potential. Explain Name the lobes of the cerebral cor- interneurons, and a motor fiber.
the steps of an action potential. How is tex, and state their functions. De- (pp. 181–184)
it propagated? Why do myelinated fi- scribe the primary motor area and 13. Contrast the actions of the sympathetic
bers have a faster speed of conduc- the primary somatosensory area. and the parasympathetic divisions of
tion? (pp. 165–168) (pp. 173–176) the autonomic system. (pp. 184–186)
5. How is the nerve impulse transmitted 9. What is the limbic system, and what is 14. What role does the nervous system
across a synapse? Name two its function? (p. 178) play in homeostasis? (pp. 187–188)
e. c.
i.
h.
j.
Learning Outcomes After you have studied this chapter, you should be able to:
193
2 muscle fiber
quadriceps
bundle of
muscle
muscle fibers
tendon
epidermis
free nerve endings
(pain, heat, cold)
Meissner
corpuscles (touch)
Pacinian corpuscles
(pressure)
Krause end
bulbs (touch)
Ruffini endings
(pressure)
dermis
root hair
plexus (touch)
The three different types of cutaneous receptors that are sen- and contain lacy networks of nerve fibers. Ruffini endings can be
sitive to pressure are Pacinian corpuscles, Ruffini endings, and found in the dermis and hypodermis, and in joint capsules as well.
Krause end bulbs. Pacinian corpuscles are onion-shaped sensory Krause end bulbs are located in the superficial layers of the dermis.
receptors that lie deep inside the dermis. Ruffini endings and The skin’s temperature receptors are simply free nerve end-
Krause end bulbs are encapsulated by sheaths of connective tissue ings in the superficial dermis and epidermis. Some free nerve
a.
tonsils epiglottis
sensory nerve fiber taste cell taste pore
10 μm
papillae
Sense of Smell Have you ever noticed that a certain aroma vividly brings to mind
a certain person or place, and can re-create emotions you felt about that
Our sense of smell is dependent on olfactory cells located within person or place? The smell of a certain cologne might depress you by
olfactory epithelium high in the roof of the nasal cavity (Fig. 9.4). reminding you of a failed relationship, or the smell of boxwood might
Olfactory cells are modified neurons. Each cell ends in a tuft of create happier emotions because it reminds you of your grandfather’s
about five olfactory cilia, which bear receptor proteins for odor farm. The olfactory bulbs have direct connections with the limbic sys-
molecules. The brain distinguishes odors after odor molecules bind tem and its centers for emotion and memory. For example, one investi-
to the receptor proteins. gator conducted an experiment in which his subjects smelled an orange
while viewing a painting. Afterward, the descriptions of the painting’s
How the Brain Receives Odor Information details that the subjects shared were much more accurate and vivid.
Each olfactory cell has only one type out of more than 1,000 different
types of receptor proteins. Nerve fibers from olfactory cells lead
to neurons in the olfactory bulb, an extension of the brain. An Begin Thinking Clinically
odor contains many odor molecules, which activate a character- An uncinate fit is an olfactory hallucination in which the
istic combination of receptor proteins. For example, a rose might brain “tricks” the person into smelling odors that have no
release a certain combination of odor molecules, designated by cause. The hallucinations are usually unpleasant. For exam-
the blue and green spheres in Figure 9.4, while a carnation might ple, the sufferer might smell spoiled meat even when there
release a different combination. The odor's signature in the olfac- is none nearby. What lobe of the brain might be affected in
tory bulb is determined by which neurons are stimulated. When this condition? What might cause the phenomenon?
the neurons communicate this information via the olfactory tract to Answer and discussion in Appendix A.
the olfactory areas of the cerebral cortex, we know we’ve smelled
a rose or a carnation. As you know from Chapter 8, the olfactory
nerve is cranial nerve I, and the olfactory cortex is located in the Sense of Taste and Sense of Smell
temporal lobe. Some areas of the olfactory cortex receive smell The senses of taste and smell work together to create a combined
sensations; other areas contain olfactory memories. effect when interpreted by the cerebral cortex. For example,
olfactory bulb
olfactory epithelium
bone of
nasal cavity skull
odor
axons of
molecules
olfactory cells
olfactory
epithelium
a.
Figure 9.4 Olfactory cell location and anatomy. (a) The olfactory
epithelium in humans is located in the nasal cavity. (b) Olfactory cells end in
cilia that bear receptor proteins for specific odor molecules. The cilia of each supporting olfactory
olfactory cell can bind to only one type of odor molecule (signified here by cell cell
color). For example, if a rose causes olfactory cells sensitive to “blue” and olfactory cilia of
olfactory cell
“green” odor molecules to be stimulated, then neurons designated by blue b.
and green in the olfactory bulb are activated. The primary olfactory area of the odor molecules
cerebral cortex interprets the pattern of stimulation as the scent of a rose.
when you have a cold, you think food has lost its taste, but most 5. As you know from Section 2.2, many common poisons are
likely you’ve lost the ability to sense its smell. These senses water-soluble salts. Most have an alkaline pH. Based on
work together because each sensory pathway travels through that information, which taste buds would have to be the
the limbic system (see page 178 in Chapter 8). Cooperation most sensitive in order to enable someone to taste a poi-
between smell and taste signals protects us in several ways. son, and then reject it?
Appealing tastes and smells stimulate appetite, help to remind 6. Select a correct statement about the sense of smell:
you that it’s time to eat, and make eating a pleasurable activity a. Taste and smell sensations travel through some of the
(other signal pathways for hunger are discussed in Chapter 15). same brain areas.
By contrast, the smell and taste of spoiled or contaminated food b. Olfactory epithelium is located right at the entrance to the
or drink are an early warning system that helps to defend you nasal cavity.
from becoming sick—you reject the food before you actually c. An odor is made by a single type of odor molecule.
swallow it. d. a and c
e. All of the above.
Answers in Appendix A.
Content CHECK-UP!
4. Which of the following statements about the sensation of taste
is correct? 9.3 Sense of Vision
a. Taste buds are located in the back of the throat (pharynx). 6. Describe the anatomy and function of the accessory organs of the
eye.
b. Taste buds respond to five primary taste sensations. 7. Detail the anatomy of the eye, and give a function of each part.
c. Taste buds are a type of chemoreceptor. 8. Describe the sensory receptors for sight, their mechanism of action,
d. a and b and the mechanism for stereoscopic vision.
9. Discuss some common disorders of sight.
e. All of the preceding statements are correct.
lacrimal
gland
orbicularis oculi ducts of
levator palpebrae muscle lacrimal
superioris muscle eyebrow gland
superior rectus
muscle
conjunctiva
nasolacrimal lacrimal
duct sac
CN II (optic) pupil
cornea eyelashes
lens
iris
b.
a.
Figure 9.5 Accessory structures of the orbit. (a) Sagittal section of the eye and orbit. (b) The lacrimal apparatus. The blue
arrows show the path that tears follow as they move across the eye surface.
sclera
choroid
retina
optic disk
ciliary body
retinal blood
vessels lens
iris
optic nerve
pupil
fovea centralis
cornea
posterior compartment
anterior
filled with vitreous humor
compartment
filled with
aqueous humor
retina suspensory
choroid ligament
sclera
Figure 9.7 Anatomy of the human eye. Notice that the sclera, the outer layer of the eye, becomes the cornea and that
the choroid, the middle layer, is continuous with the ciliary body and the iris. The retina, the inner layer, contains the photoreceptors for
vision; the fovea centralis is the region where vision is most acute. The retina is supplied with a network of tiny blood vessels.
What's New
Detecting Alzheimer Disease with Eye Exams
As mentioned in the Medical Focus in Chapter 8, Alzheimer disease is office. Fluorescent drops are then applied, and the lenses are re-
a progressive, incurable disease of the brain. Researchers now believe examined. The dye binds to amyloid, thus showing any protein
that the disease process begins over a decade before the first signs start accumulation. Additional tests use precise measurements of blood
to appear. Currently, Alzheimer disease is diagnosed by its symptoms— flow in retinal vessels. These studies have shown that the amount
forgetfulness, confusion, mood changes—all of which worsen over and velocity of blood flow diminishes in Alzheimer disease. Along
time. Available treatments merely delay the patient’s inevitable slow with blood flow studies, researchers are now employing improved
decline. Currently, a definitive diagnosis of the disease can only be retinal scanning technology to accurately view the outermost periph-
made at autopsy, when the patient’s brain can be physically examined. eral areas of the retina. (Previously, examination techniques did not
Several new diagnostic techniques offer the promise of a much allow for precise examination of the entire peripheral retina to be
earlier diagnosis of Alzheimer disease. Neurologists have known for made.) In these outlying retinal areas, deposits of cellular debris
some time that the amyloid protein, which destroys the brains of called drusen accumulate. Though drusen naturally accumulates
Alzheimer victims, can also be observed in the lenses of late-stage with aging, the amount of drusen in the peripheral retina is higher
patients. The condition is called Alzheimer cataract. One new test for individuals with Alzheimer disease.
takes advantage of this fact by employing laser eye scan technology Developers of these technologies envision yearly screening exams,
to detect the early presence of amyloid protein in the lenses of much much like mammograms or prostate exams. Most importantly, earlier
younger, seemingly healthy patients. First, the patient’s lenses are detection may lead to a better understanding of the disease, which may
studied using exams similar to those performed in an optometrist’s then allow effective preventative treatments to be developed.
a. Focusing
ciliary body
ciliary muscle relaxed
ciliary muscle contracted
lens flattened
lens rounded
light rays
Figure 9.8 Focusing. (a) Light rays from each point on an object are bent by the cornea and the lens in such a way that an
inverted and reversed image of the object forms on the retina. (b) When focusing on a distant object (such as the tree) the lens is flat
because the ciliary muscle is relaxed and the suspensory ligament is taut. (c) When focusing on a near object, the lens accommodates; it
becomes rounded because the ciliary muscle contracts, causing the suspensory ligament to relax.
retinal
inner segment
cell body
opsin
nucleus
membrane Rhodopsin molecule
synaptic of disk
synaptic endings (opsin + retinal)
vesicles
a. 20 µm b.
Figure 9.9 Photoreceptors in the eye. (a) The outer segment of rods and cones contains stacks of membranous disks, which
contain visual pigments. In rods, the membrane of each disk contains rhodopsin, a complex molecule containing the protein opsin and
the pigment retinal. (b) When retinal absorbs light energy, it splits, releasing opsin, which sets in motion a cascade of reactions that cause
ion channels in the plasma membrane to close. Thereafter, nerve signals go to the brain.
choroid
rod cell
and cone
cell layer
bipolar
retina cell layer
optic
nerve
ganglion
cell layer
a. Location of retina
Figure 9.10 Structure and function of the retina. (a) The retina is the inner layer of the eyeball. Rod cells and cone cells, located at
the back of the retina nearest the choroid, synapse with bipolar cells, which synapse with ganglion cells. Integration of signals occurs at these
synapses; therefore, much processing occurs in bipolar and ganglion cells. Further, notice that many rod cells share one bipolar cell, but cone
cells do not. Certain cone cells synapse with only one bipolar cell. Cone cells, in general, distinguish more detail than do rod cells. (b) This micro-
graph shows that the sclera and choroid are relatively thin compared to the retina, which is composed of several layers of cells.
rod cells and cone cells; the middle layer contains bipolar cells; nerve signals received from the center of its receptive field; otherwise,
and the innermost layer contains ganglion cells, whose sensory fi- it is inhibited. If all the rod cells in the receptive field receive light,
bers become the optic nerve. Only the rod cells and the cone cells the ganglion cell responds in a neutral way—that is, it reacts only
are sensitive to light, and therefore light must penetrate to the back weakly or perhaps not at all. In this way, visual signals are processed
of the retina before they are stimulated. and refined in the retina before nerve signals are sent to the brain. The
The rod cells and the cone cells synapse with the bipolar majority of integration occurs in the visual areas of the cerebral cortex.
cells, which in turn synapse with ganglion cells that initiate nerve
Blind Spot In Figure 9.10, you can see that there are no rods and
signals. Notice in Figure 9.10 that there are many more rod cells
cones where the optic nerve exits the retina. Therefore, no vision is
and cone cells than ganglion cells. In fact, the retina has as many as
possible in this area. You can prove this to yourself by putting a dot
150 million rod cells and 6 million cone cells but only one million
to the right of center on a piece of paper. Use your right hand to
ganglion cells. The sensitivity of cones versus rods is mirrored by
move the paper slowly toward your right eye while you look straight
how directly they connect to ganglion cells. As many as 150 rods
ahead. The dot will disappear at one point—when its image falls on
may activate the same ganglion cell. It’s no wonder stimulation of
the retina where receptors are absent. This is your blind spot.
rods results in vision that’s blurred and indistinct. In contrast, some
cone cells in the fovea centralis activate only one ganglion cell. From the Retina to the Visual Cortex As stated, sensory fi-
This explains why cones, especially in the fovea, provide us with a bers from the ganglion cells in the retina assemble to form the op-
sharper, more detailed image of an object. tic nerves. The optic nerves carry nerve signals from the eyes to
As signals pass to bipolar cells and ganglion cells, integration the optic chiasma. The optic chiasma has an X-shape formed by a
occurs. Each ganglion cell receives signals from rod cells covering crossing over of some of the optic nerve fibers. At the chiasma,
about one square millimeter of retina (about the size of a thumbtack fibers from the right half of each retina converge and continue on
hole). This region is the ganglion cell’s receptive field. Some time together in the right optic tract, and fibers from the left half of each
ago, scientists discovered that a ganglion cell is stimulated only by retina converge and continue on together in the left optic tract.
Normal vision is commonly designated as 20/20. This ratio is In rare cases, the lens itself may take on this oblong shape. The
determined using a Snellen chart, which uses letters of different light rays cannot be evenly focused on the retina; thus, the image
sizes to test visual acuity (alternative charts for children or illiter- is blurred. This condition, called astigmatism, can be corrected
ate individuals use symbols). The numerator of the ratio is always by an unevenly ground lens to compensate for the uneven cornea
the distance from the chart: 20 feet. The denominator is the dis- (Fig. 9Ac).
tance at which a normal individual can read the letter: 20 feet.
The larger this number, the poorer the subject’s vision.
Thus, a person with 20/200 vision must stand 20 feet
away to read a letter that the normal person can read at
200 feet. (In countries that use metric measures, normal
vision is 6/6.) Younger people may actually have vision
that is better than 20/20; 20/15 vision is not uncommon
in teenagers and young adults. Persons who can see close normal
objects but cannot see the letters from this distance have eyeball
myopia—that is, nearsightedness. Nearsighted people
can see close objects better than they can see objects at a Long eyeball; rays focus in front of Concave lens allows subject
distance. These individuals have an elongated eyeball, retina when viewing distant objects. to see distant objects.
and when they attempt to look at a distant object, the a. Near
Nearsight
sightedness
sight edness
image is brought to focus in front of the retina (Fig. 9Aa).
They can see close objects because they can adjust the
lens to allow the image to focus on the retina, but to see
distant objects, these people must wear concave lenses,
which spread the light rays so that the image can be
focused on the retina. normal
Rather than wear glasses or contact lenses, many eyeball
nearsighted people are now choosing to have laser sur-
Short eyeball; rays focus behind Convex lens allows subject
gery. First, specialists determine how much the cornea
retina when viewing close objects. to see close objects.
needs to be flattened to achieve visual acuity. Con-
trolled by a computer, the laser then removes this b. Fa
Farrsight
sightedness
edness
amount of the cornea. Most patients achieve at least
20/40 vision, but a few complain of glare, varying
visual acuity and chronic dry eyes.
Persons who can easily see the optometrist’s chart but
cannot see close objects well have hyperopia—that is,
farsightedness. These individuals can see distant objects
better than they can see close objects. They have a short-
ened eyeball, and when they try to see close objects, the Uneven cornea; Uneven lens allows subject
image is focused behind the retina (Fig. 9Ab). When the rays do not focus evenly. to see objects clearly.
ly
ly.
object is distant, the lens can compensate for the short eye- c. Astigmatism
ball, but when the object is close, these persons must wear
a convex lens to increase the bending of light rays so that Figure 9A Common abnormalities of the eye, with possible
the image can be focused on the retina. corrective lenses. (a) A concave lens in nearsighted persons focuses
In some individuals, the cornea assumes an oval light rays on the retina. (b) A convex lens in farsighted persons focuses
shape along one axis (imagine a football-shaped cor- light rays on the retina. (c) An uneven lens in persons with astigmatism
focuses light rays on the retina.
nea, instead of the normal round “tennis ball” shape).
Vision is a human being’s strongest sense. When we study the eye, and colors may look faded (Fig. 9B). So-called “wet” MD results
it’s impressive to discover what a complex structure it is. Blindness from abnormal growth of new blood vessels around the macula.
can result from damage to structures involved in the pathway on The blood vessels leak serum and blood, causing severe scarring
which light travels to reach the retina, or by damage to the retina itself. and macular destruction. “Dry” MD, in which blood vessel growth
Light must first pass through the cornea to enter the eye, and doesn’t occur, usually precedes the wet form. Vision loss is less
scarring of the cornea can dim or distort incoming light signals. Com- severe in dry MD. A family history of MD, smoking, hypertension,
mon causes for corneal scarring include injury and/or infection. Cor- lighter eye color, and excessive sunlight exposure are all risk factors
neal transplants, using cadaver corneas, can often restore vision. Light for MD. Vitamin and mineral supplements, especially vitamin C
next passes through the lens as it continues in its path to the retina. A and zinc, may help slow the progression of dry MD. When wet MD
cataract occurs when the lens of the eye becomes clouded, making is diagnosed early, laser treatment can sometimes stop abnormal
it difficult to read, drive, or see details distinctly. Cataract develop- blood vessel growth.
ment increases with age, but smoking and excessive sunlight exposure Like macular degeneration, diabetic retinopathy is caused by
are also known risk factors. Fortunately, the lenses of cataract patients damage to retinal blood vessels. Diabetic retinopathy is a common
can be replaced with an artificial lens implant. When replacement complication of poorly controlled diabetes mellitus—almost half of
isn’t possible, the lenses can be removed entirely. The patient will then all diabetes patients have some degree of diabetic retinopathy. At first,
see by using special glasses. the diabetic person may notice only a mild vision loss, but blurred or
The aqueous humor in the eye’s anterior chamber is continually reduced vision (especially night vision) develop as the disease pro-
being produced and then drained. When a person has glaucoma, the gresses. As damaged blood vessels bleed into the retina and surround-
drainage ducts are blocked and aqueous humor builds up. Without ing cells, the retina may detach. Laser surgery is often necessary to
medication and/or surgical treatment, the resulting pressure inside the stop bleeding and repair a detached retina.
eye compresses the retinal arteries. Retinal cells begin to die due to The retina can also be dislodged from the choroid layer under-
lack of nutrients, and the person becomes partially blind. Eventually, neath by a sharp blow to the eye (for example, being struck by a ball
total blindness can result. during a baseball game). Because detachment interrupts blood sup-
If the retinal photoreceptors are destroyed, a person will be ply, retinal cells will die. Permanent blindness can be prevented by
blind, even if the rest of the visual pathway is undamaged. The most laser reattachment surgery. Tragically, retinal detachment, hemor-
common cause of blindness resulting from retinal damage is age- rhage, blindness, and severe brain damage occur in very young
related macular degeneration (MD). You’ll remember that the children who are victims of shaken baby syndrome (see Focus on
macula (macula lutea, page 201) contains the fovea centralis, where Forensics, p. 208).
cone cells are concentrated. Individuals with macular degeneration A yearly eye examination assists in the early detection of many
have a distorted visual field: Blurriness or a blind spot is present, eye diseases, including diabetic retinopathy, macular degeneration,
straight lines might look wavy, objects look distorted or wrinkled, cataracts, and glaucoma.
optic nerve
macula fovea
lutea centralis
Scene viewed by someone with normal vision Same scene viewed by someone with macular
degeneration
Figure 9B When a person with macular degeneration looks at a scene, the objects may look larger or smaller than they
really are. Colors will appear dimmer, and there may be areas that look gray and wrinkled.
optic chiasma
optic nerves
The optic tracts sweep around the hypothalamus, and most areas. In other words, the visual field has been taken apart even though
fibers synapse with neurons in nuclei (masses of neuron cell bod- we see a unified field. The visual association areas are believed to re-
ies) in the thalamus. Axons from the thalamic nuclei form optic build the field and give us an understanding of it. Visual association
radiations that take nerve signals to the primary visual areas of areas also store visual memories of objects previously seen.
the occipital lobes (Fig. 9.11). The occipital lobes are a part of the
cerebral cortex (see Fig. 8.9). Content CHECK-UP!
The visual cortex consists of the primary visual area and
the visual association areas of the occipital lobes. Notice that the 7. The posterior compartment of the eye is filled with:
image arriving at the thalamus, and therefore the primary visual a. aqueous humor. c. blood.
areas, has been split because the left optic tract carries information b. tears. d. vitreous humor.
about the right portion of the visual field and the right optic tract 8. Which statement is true?
carries information about the left portion of the visual field. There- a. Rod cells can be found in the fovea.
fore, the right visual and left visual cortex must communicate with
b. Light stimulus to rod cells stops the release of
each other for us to see the entire visual field. Because the image
neurotransmitter from the rods.
is inverted and reversed (see Figs. 9.8 and 9.11) it must be righted
for us to correctly perceive the visual field. Additionally, inputs c. Cone cells provide peripheral vision.
from each half of the visual cortex are viewed at slightly differ- d. Cone cells are spread evenly throughout the retina.
ent angles. This creates stereoscopic visions, the impression of 9. Imagine that you're looking at your computer screen. After the
three-dimensional width and depth. visual image has reached the fovea centralis, describe the
The most surprising finding has been that each primary vi- nerve path that the image must take through your brain as it
sual area of the cerebral cortex acts like a post office, parceling travels to the visual cortex.
out information regarding color, form, motion, and possibly other Answers in Appendix A.
attributes to different portions of the adjoining visual association
9.4 Sense of Hearing which extends from each middle ear to the nasopharynx (area at
the back of the throat, which joins the nasal cavity), allows us to
10. Detail the anatomy of the ear, and give a function of each part.
equalize air pressure. Chewing gum, yawning, and swallowing in
11. Describe the sensory receptors for hearing and their mechanism
of action. elevators and on airplanes help to move air through the auditory
tubes upon ascent and descent. As this occurs, we often hear our
The ear has two sensory functions: hearing and equilibrium (bal- ears “pop.”
ance). The sensory receptors for both of these are located in the inner The inner ear lies in the bony labyrinth, a delicately carved
ear, and each consists of hair cells with stereocilia (long micro- cavity within the temporal bone of the skull. Lining the bone is
villi) that are sensitive to mechanical stimulation. The hair cells are a tube of tissue called the membranous labyrinth. Two distinct
mechanoreceptors, which respond to pressure or body movement. fluids are found in the inner ear: The space between the bony
labyrinth and the membranous labyrinth contains perilymph (a
fluid similar to cerebrospinal fluid) and the membranous laby-
Anatomy and Physiology of the Ear rinth is filled with endolymph. The inner ear is divided into three
Figure 9.12 shows that the ear has three divisions: outer, middle, areas: the semicircular canals, the vestibule, and the cochlea. The
and inner. The outer ear consists of the pinna (external flap) and semicircular canals and the vestibule are both concerned with
the external auditory canal. The opening of the auditory canal is equilibrium and the cochlea is involved with hearing. The cochlea
lined with fine hairs and sweat glands. Modified sweat glands are resembles the shell of a snail because it spirals.
located in the upper wall of the canal. There, they secrete cerumen,
or earwax, a substance that helps guard the ear against the entrance Sound Pathway
of foreign materials, such as air pollutants. Sound waves pass through the auditory canal and middle ear to the
The middle ear is carved into the temporal bone of the cochlea in the inner ear, which transforms them into nerve signals
skull. It begins at the tympanic membrane (eardrum). Three conducted in the auditory nerve to the brain.
tiny bones, collectively called the auditory ossicles, are found in
the middle ear. Individually, they are the malleus (hammer), the Through the Auditory Canal and Middle Ear The process of
incus (anvil), and the stapes (stirrup) because their shapes re- hearing begins when sound waves enter the auditory canal. Just as
semble these objects. The malleus attaches to the tympanic mem- ripples travel across the surface of a pond, sound waves travel by
brane, then forms a joint with the incus. In turn, the incus then the successive vibrations of air molecules. Sound waves do not
connects to the stapes. The stapes fastens to the oval window—a usually carry much energy, but when a large number of waves
small, membrane-covered opening in the bone of the inner ear. strike the tympanic membrane, it moves back and forth (vibrates)
Another, even smaller membrane, the round window, is also ever so slightly. The malleus then vibrates from the pressure wave
located in this bone. The round window helps to diminish pres- from the inner surface of the tympanic membrane, in turn vibrating
sure waves in the inner ear. An auditory tube (Eustachian tube), the incus and then the stapes. The slight pressure wave is multiplied
vestibular
nerve
pinna
cochlear
nerve
tympanic cochlea
membrane
auditory
canal temporal
bone
round window
auditory
tube
Figure 9.12 Anatomy of the human ear. The outer ear consists of the pinna and the auditory canal. In the middle ear, the
malleus (hammer), the incus (anvil), and the stapes (stirrup) amplify sound waves. In the inner ear, the mechanoreceptors for equilibrium
are in the semicircular canals and the vestibule, and the mechanoreceptors for hearing are in the cochlea.
about 20 times as it moves from bone to bone. Finally, the stapes with neurons of the cochlear nerve (part of cranial nerve VIII,
strikes the membrane of the oval window, causing it to vibrate. In called the vestibulocochlear, or auditory, nerve). Bending the ste-
this way, the pressure wave is passed to the perilymph within the reocilia of a hair cell causes changes in the amount of signaling
cochlea of the inner ear. from the hair cell to the neuron, and this affects the frequency of
action potentials that are generated in the neuron. Action potential
From the Cochlea to the Auditory Cortex If the cochlea is signals are transmitted into the brain stem, where they are relayed
unwound and examined in cross section (Fig. 9.13), you can see through the thalamus to the auditory cortex in the temporal lobe.
that it has three ducts: the vestibular duct, the cochlear duct, and There, the signals are interpreted as sound. Auditory memories of
the tympanic duct. Both the vestibular and tympanic ducts are the sounds we’ve heard in the past, such as the earworms discussed
filled with perilymph, while the cochlear duct is filled with endo- in the chapter introduction, are also housed in the temporal lobe.
lymph. The sense organ for hearing, called the spiral organ (organ Each part of the spiral organ is sensitive to different wave fre-
of Corti), is located in the cochlear duct. The spiral organ consists quencies, or pitches. Near the tip, the spiral organ responds to low
of tiny hair cells rooted in a basilar membrane. A gelatinous mate- pitches, such as a tuba, and near the base, it responds to higher
rial called the tectorial membrane sits above the hair cells, and pitches, such as a bell or a whistle. The nerve fibers from each
their stereocilia are embedded in this membrane. region along the length of the spiral organ lead to slightly different
When the stapes strikes the membrane of the oval window, areas in the brain. The pitch sensation we experience depends upon
pressure waves in the perilymph travel from the vestibular duct to which region of the basilar membrane vibrates and which area of
the tympanic duct across the basilar membrane. The basilar mem- the auditory cortex is stimulated.
brane moves up and down, and the stereocilia of the hair cells Volume is a function of the amplitude (height) of sound waves.
embedded in the tectorial membrane bend. Hair cells communicate Loud noises cause the fluid within the vestibular canal to exert more
cochlear
duct (endolymph)
tympanic
9.5 Sense of Equilibrium
duct (perilymph) 12. Describe the sensory receptors for equilibrium and their mechanism
cochlear of action.
nerve
cochlea
utricle
saccule
endolymph
cupula
otoliths
stereocilia
hair cell
supporting cell
supporting
vestibular nerve cell
vestibular
nerve
flow of endolymph
flow of otolithic
membrane
kinocilium
stereocilia
a. Rotational equilibrium: receptors in ampullae of semicircular duct b. Gravitational equilibrium: receptors in utricle and saccule of vestibule
Figure 9.14 Rotational (dynamic) and gravitational (static) equilibrium. (a) Rotational equilibrium. The ampullae of the
semicircular ducts contain hair cells with stereocilia embedded in a cupula. When the head rotates, the cupula is displaced, bending the
stereocilia. Thereafter, nerve signals travel in the vestibular nerve to the brain. (b) Gravitational equilibrium. The utricle and the saccule
contain hair cells with stereocilia embedded in an otolithic membrane. When the head bends, otoliths are displaced, causing the
membrane to sag and the stereocilia to bend. If the stereocilia bend toward the kinocilium, the longest of the stereocilia, nerve signals
increase in the vestibular nerve. If the stereocilia bend away from the kinocilium, nerve signals decrease in the vestibular nerve. The
difference tells the brain in which direction the head moved.
There are two major types of deafness: conduction deafness and sen- the hunter uses to support the gun. Even listening to city traffic for
sorineural, or nerve, deafness. Conduction deafness occurs when extended periods can damage hearing, and frequent attendance at rock
a mechanical blockage keeps sound waves from reaching the oval concerts and constant listening to loud music from an MP3 player (such
window, the membrane at the beginning of the inner ear. Conductive as an IPod®) are obviously dangerous. The danger is compounded by
deafness can result from the presence of foreign objects in the exter- using earbuds tightly fitted into the external ear canal. Noisy indoor or
nal ear canal, impacted ear wax, or cancerous tumors in the external outdoor equipment, such as a rug-cleaning machine or a chain saw, is also
ear canal or middle ear. Conduction deafness can also be due to troublesome. Even motorcycles and recreational vehicles, such as snow-
repeated infections or otosclerosis. With otosclerosis, the normal mobiles and motocross bikes, can contribute to a gradual hearing loss.
bone of the middle ear is replaced by vascular, spongy bone. The first hint of a problem could be temporary hearing loss, a
Nerve deafness most often occurs when cilia on the receptors “full” feeling in the ears, muffled hearing, or tinnitus (ringing in the
within the cochlea have worn away. Because this may happen with nor- ears). If you have any of these symptoms, modify your listening habits
mal aging, older people are more likely to have trouble hearing. How- immediately to prevent further damage. If exposure to noise is unavoid-
ever, studies also suggest that age-associated hearing loss can be slowed, able, use specially designed noise-reduction earmuffs or purchase ear-
or even prevented, if ears are protected from loud noises, starting even plugs made from a compressible, sponge-like material at a drugstore or
during infancy. Hospitals are now aware of the problem and are taking sporting goods store. These earplugs are not the same as those worn for
steps to ensure that neonatal intensive care units and nurseries are as swimming, and they should not be used interchangeably.
quiet as possible. Sensorineural deafness may also result from congeni- Finally, people need to be aware that some medicines are ototoxic
tal defects, particularly when a pregnant woman contracts German (damaging to any of the elements of hearing or balance). Anticancer
measles (rubella) during the first trimester of pregnancy. For this rea- drugs—most notably, cisplatin—and certain antibiotics (for example,
son, every female should be immunized against rubella before her child- streptomycin, kanamycin, and gentamicin) make the ears especially sus-
bearing years (see the Medical Focus: Immunization: The Great ceptible to a hearing loss. Hearing loss has also occurred in men who take
Protector in Chapter 13 for information regarding immunizations). drugs for erectile dysfunction (Viagra,TM Cialis, TM and Levitra TM). Peo-
In today’s society, exposure to the types of noises listed in Table 9A ple taking such medications should protect their ears from any excessive
is common. Everyone should consider three aspects of noise to prevent noise, and they should discontinue taking the medication and contact a
hearing loss: (1) how loud the noise is (2) how long the noise is heard, and health care professional if they notice hearing loss. It's critically important
(3) how close the noise is to the ear. Loudness is measured in decibels, for cocaine users to seek medical help for their addiction because cocaine
and any level above 80 decibels could damage the hair cells of the organ can also cause deafness (along with a host of other critical health issues).
of Corti. Exposure to intense sounds of short duration, such as a burst of Cochlear implants, which directly stimulate the auditory nerve,
gunfire, can result in an immediate hearing loss. Hunters often have sig- are available for persons with sensorineural deafness. Earlier models of
nificant hearing loss. Interestingly, the butt of the gun partially protects cochlear implants were costly, and people wearing these electronic
the adjacent ear, so hearing loss occurs in the ear opposite the shoulder devices reported that the speech they heard was very mechanical.
Newer models produce better sound quality at a much lower cost.
stopping suddenly. Inflammation of cranial nerve VIII, the ves- Appropriate motor output from the brain to various skeletal
tibulocochlear (or auditory) nerve from the ear, can cause vertigo muscles can right our present position in space.
as well. Motion sickness is also possible if the sensory input from Table 9.2 summarizes the functions of the parts of the ear.
the inner ear is different from visual sensation. For example, a
person standing inside a large ship on rough seas will sense move- Content CHECK-UP!
ment with the inner ear (as the ship tosses back and forth on the
waves), but the visual input will register no movement (because 13. Which of the following receptors are found in the semicircular
the ship’s walls don’t move relative to the person’s body). The canals, utricle, and saccule?
person is seasick, with severe nausea and vomiting. People who a. mechanoreceptors c. chemoreceptors
are seasick sometimes find relief if they stand outdoors and focus b. pressure receptors d. nociceptors
on the horizon, so that both visual and inner ear inputs to the brain
14. The vestibule generates action potentials that determine
signal movement. _____ equilibrium, while the semicircular canals generate ac-
tion potentials that determine _____ equilibrium.
Gravitational Equilibrium Pathway Answers in Appendix A.
Summary
8.1 General Senses generated and transmitted to the spinal A. Proprioceptors are mechanore-
Each type of sensory receptor detects cord and/or brain. Sensation occurs ceptors involved in reflexes that
a particular kind of stimulus. When stim- when nerve signals reach the cerebral maintain muscle tone, equilib-
ulation occurs, sensory receptors initiate cortex. Perception is an interpreta- rium, and posture.
receptor potentials. Action potentials are tion of the meaning of sensations.
Study Questions
1. Name the five different types of gen- 4. How are somatic and visceral nocicep- 7. Describe the protective accessory eye
eral sensory receptors. (p. 194) tors alike? How are they different? structures. How does each work to pre-
2. Name two types of proprioceptors. (p. 196) vent eye damage? (p. 199)
What is their general function in the 5. Name the receptors for the senses of 8. How many pairs of extrinsic eye mus-
body? (pp. 194–195) taste and smell. Which brain areas re- cles are there? What movements does
3. Name three types of cutaneous receptors ceive their sensory information? each pair cause? (pp. 199–200)
that are sensitive to fine touch, and three (pp. 196–197) 9. What are the eye's three layers?
that are sensitive to pressure. Where is 6. Describe the relationship between Which contains photoreceptors?
each type found? (pp. 194–195) taste and smell. (pp. 197–198) (pp. 200–201)
Learning Outcomes After you have studied this chapter, you should be able to:
10.1 Endocrine Glands hormones. Describe the effects of 18. Discuss atrial natriuretic hormone,
thyroid abnormalities. leptin, ghrelin, growth factors, and
1. Define a hormone, and state the prostaglandins as hormones not
function of hormones. 9. Discuss the function of parathyroid
hormone, and describe the effects of produced by endocrine glands.
2. Discuss the difference in mode of parathyroid hormone abnormalities.
action between peptide and steroid 10.7 The Importance of Chemical
hormones. 10.4 Adrenal Glands Signals
3. Name the major endocrine glands, 19. Give examples to show that chemical
10. Describe the anatomy of the adrenal
and identify their locations. signals can act between organs,
glands.
4. Discuss the control of glandular cells, and individuals.
11. Discuss the function of the adrenal
secretion by humoral, hormonal, and
medulla and its relationship to the
nervous mechanisms, and give an
nervous system. 10.8 Effects of Aging
example of how negative feedback 20. Discuss the anatomical and
functions in these control mechanisms. 12. Name three categories of hormones
produced by the adrenal cortex, give physiological changes that occur in
the endocrine system as we age.
10.2 Hypothalamus and Pituitary an example of each category, and
discuss their actions. Describe the
Gland effects of adrenal cortex malfunction. 10.9 Homeostasis
5. Explain the anatomical and functional 21. Discuss how the endocrine system
relationships between the 10.5 Pancreas works with other systems of the
hypothalamus and the pituitary gland. 13. Describe the anatomy of the pancreas. body to maintain homeostasis.
6. Name and discuss two hormones
produced by the hypothalamus that
14. Name three hormones produced by Visual Focus
the pancreas, and discuss their
are secreted by the posterior pituitary. The Hypothalamus and the Pituitary
functions.
7. Name the hormones produced by 15. Discuss the two types of diabetes I.C.E.—In Case of Emergency
the anterior pituitary, and describe mellitus, and contrast hypoglycemia
their function. Indicate which of Insulin Shock and Diabetic Ketoacidosis
with hyperglycemia.
these hormones control other What’s New
endocrine glands. 10.6 Additional Endocrine Options for Diabetics: The Artificial Pancreas System,
10.3 Thyroid and Parathyroid Glands Beta Cell Transplants, and the BioHub
Glands 16. Name the most important male and Medical Focus
female sex hormones. Discuss their
8. Discuss the anatomy of the thyroid functions. Side Effects of Anabolic Steroids
gland, and the chemical structure
and physiological function of its 17. State the location and function of the Human Systems Work Together
pineal gland and the thymus gland. Endocrine System
217
PITUITARY GLAND
Posterior Pituitary
Release ADH and oxytocin produced
by the hypothalamus
PARATHYROIDS
Anterior Pituitary Parathyroid hormone (PTH):
Thyroid stimulating (TSH): raises blood calcium level
stimulates thyroid
Adrenocorticotropic (ACTH):
stimulates adrenal cortex parathyroid glands
Gonadotropic (FSH, LH): egg and (posterior surface of thyroid)
sperm production; sex hormone
production
Prolactin (PL): milk production
Growth (GH): bone growth, protein
synthesis, and cell division
THYMUS GLAND
Thymosins: production and
maturation of
THYROID GLAND T lymphocytes
Thyroxine (T 4) and triiodothyronine
(T3): increase metabolic rate;
regulates growth and development
PANCREAS
Calcitonin: lowers blood calcium level
Insulin: lowers blood glucose
level; formation of glycogen
Glucagon: increases blood
ADRENAL GLAND glucose level; breakdown of
Adrenal cortex glycogen
Glucocorticoids (cortisol):
raises blood glucose level;
stimulates breakdown of protein
GONADS
Mineralocorticoids (aldosterone):
reabsorption of sodium and Testes
excretion of potassium Androgens (testosterone):
Sex hormones: reproductive organs male sex characteristics
and bring about sex characteristics Ovaries
Adrenal medulla Estrogens and progesterone:
testis female sex characteristics
Epinephrine and norepinephrine:
(male)
active in emergency situations;
raise blood glucose level
ovary (female)
Figure 10.1 Anatomical location of major endocrine glands in the body. The hypothalamus, pituitary, and pineal glands are
in the brain, the thyroid and parathyroids are in the neck, and the adrenal glands and pancreas are in the abdominal cavity. The gonads
include the ovaries in females, located in the pelvic cavity, and the testes in males, located outside this cavity in the scrotum. The thymus
gland lies within the thoracic cavity.
peptide hormone
(first messenger)
cytoplasm
2. Hormone binds
to receptor inside
nucleus.
2. Binding leads to
activation of an protein
enzyme that changes receptor
ATP to cAMP. DNA protein
mRNA ribosome
cAMP
ATP (second messenger)
plasma
membrane
3. cAMP activates an
enzyme cascade. glucose
(leaves cell
and goes
to blood) 3. Hormone-receptor mRNA
complex activates
4. Many molecules of gene and synthesis
glycogen are broken of a specific mRNA 4. mRNA moves to
down to glucose, glycogen
molecule follows. ribosomes, and protein
which enters the synthesis occurs.
bloodstream.
Figure 10.2 Action of a peptide hormone. The bind- Figure 10.3 Action of a steroid hormone. A steroid
ing of a peptide hormone leads to cAMP and then to activation of hormone results in a hormone-receptor complex that activates
an enzyme cascade. In this example, the hormone causes glyco- DNA and protein synthesis.
gen to be broken down to glucose.
of this chapter, you’ll learn about other instances in which pairs of It’s important to stress that many hormones are influenced
hormones work opposite to one another, and thereby bring about by more than one control mechanism. In the previous examples,
the regulation of a substance in the blood. you can see that insulin release is influenced by all three control-
The nervous system is an important controller of the endocrine lers: humoral, hormonal, and neural control. For the majority of
system. Upon receiving sensory information from the body, the hormones, control is regulated by negative feedback. As you know
brain can make appropriate adjustments to hormone secretion to from Chapter 1, in a negative feedback system, a stimulus causes a
ensure homeostasis. For example, while you eat a meal, sensory body response. The body response, in turn, corrects the initial stim-
information is relayed to the brain. In turn, the brain signals para- ulus. The result is that the activity of the hormone is maintained
sympathetic motor neurons to cause the release of insulin from the within normal limits and homeostasis is ensured. However, in a few
pancreas. (Recall that the parasympathetic neurons control “rest instances, positive feedback controls the release of a hormone—for
and digest” functions.) Insulin will allow body cells to take up example, release of oxytocin during labor and delivery (discussed
glucose from digested food. on page 222).
hypothalamus
Kidney tubules and Smooth muscle Mammary glands: Mammary glands: Bones, tissues: Ovaries, testes:
blood vessels: in uterus: oxytocin prolactin (PRL) growth hormone gonadotropic
antidiuretic oxytocin (GH) hormones (FSH, LH)
hormone (ADH)
Figure 10.4 The hypothalamus and the pituitary. Left: The hypothalamus produces two hormones, ADH and oxytocin,
which are stored and secreted by the posterior pituitary. Right: The hypothalamus controls the secretions of the anterior pituitary, and the
anterior pituitary controls the secretions of the thyroid, adrenal cortex, and gonads, which are also endocrine glands. It also secretes
growth hormone and prolactin.
releasing hormone
(hormone 1)
TRH Feedback
inhibits
release of
anterior pituitary hormone 1,
TRH.
Blood Ca2+
lowers.
hig
hb
loo
dC
a 2+
the thyroid gland because other tissues incorporate so little iodine in
their cells. Hyperthyroidism can also be caused by a thyroid tumor, Homeostasis (normal blood Ca2+)
which is usually detected as a lump during physical examination.
low
Again, the treatment is surgery in combination with administration blo
od
of radioactive iodine. The prognosis for most patients is excellent. Ca 2+
Calcitonin
Calcium (Ca21) plays a significant role in both nervous conduc-
tion and muscle contraction. It is also necessary for coagulation
(clotting) of blood. The blood calcium level is regulated in part
by calcitonin, a hormone secreted by the thyroid gland when the
blood calcium level rises (Fig. 10.9). The primary effect of calci- Blood Ca2+
rises.
tonin is to bring about the deposit of calcium in the bones. It does Parathyroid
this by temporarily reducing the activity and number of osteoclasts. glands
Recall from Chapter 6 that these cells break down bone. When release PTH
into blood.
the blood calcium lowers to normal, the release of calcitonin by
the thyroid is inhibited, but a low calcium level stimulates the re-
lease of parathyroid hormone (PTH) by the parathyroid glands. activated
vitamin D
Calcitonin is an important hormone in children, whose skeleton
is undergoing rapid growth. By contrast, calcitonin is of minor parathyroid
importance in adults because parathyroid hormone is the major hormone
controller of calcium homeostasis. However, calcitonin can be used (PTH)
therapeutically in adults to reduce the effects of osteoporosis (see
the Medical Focus on page 106). Intestines Kidneys Bones
absorb Ca2+ reabsorb Ca2+ release Ca2+
Parathyroid Glands from digestive from kidney into blood.
tract. tubules.
Parathyroid hormone (PTH), the hormone produced by the
parathyroid glands, causes the blood phosphate (HPO422) level Figure 10.9 Regulation of blood calcium level.
to decrease and the ionic blood calcium (Ca21) level to increase. Top: When the blood calcium (Ca21) level is high, the thyroid
The antagonistic actions of calcitonin, from the thyroid gland, and gland secretes calcitonin. Calcitonin promotes the uptake of
parathyroid hormone, from the parathyroid glands, maintain the Ca21 by the bones, and therefore the blood Ca21 level returns
blood calcium level within normal limits. to normal. Bottom: When the blood Ca21 level is low, the
Note in Figure 10.9 that after a low blood calcium level stimu- parathyroid glands release parathyroid hormone (PTH). PTH
lates the release of PTH, the hormone promotes release of cal- causes the bones to release Ca21. It also causes the kidneys
cium from the bones. (It does this by promoting osteoclast activity.) to reabsorb Ca21 and activate vitamin D; thereafter, the intes-
tines absorb Ca21. Therefore, the blood Ca21 level returns to
PTH promotes the reabsorption of calcium by the kidneys, where
normal.
it also activates a form of vitamin D called calcitriol. Calcitriol, in
226 PART III Integration and Coordination
hypothalamus
neurosecretory
cells produce Stress Response:
hypothalamic- Long Term
path of nerve releasing
impulses hormones Glucocorticoids
neuron Protein and fat metabolism
cell body instead of carbohydrate
breakdown.
anterior Reduction of inflammation;
pituitary immune cells are
sympathetic fibers secretes suppressed.
spinal cord ACTH
(cross section)
ACTH Mineralocorticoids
epinephrine
Sodium ions and water
norepinephrine are reabsorbed by kidney.
Figure 10.10 Adrenal glands. Both the adrenal medulla and the adrenal cortex are under the control of the hypothalamus
when they help us respond to stress. Left: The adrenal medulla provides a rapid, but short-term stress response. Right: The adrenal
cortex provides a slower, but long-term stress response.
Content CHECK-UP!
Blood pressure 10. From the following list of hormones of the adrenal cortex and their
drops. corresponding effects, choose the pair, or pairs, that are correct.
a. male hormones → stimulate sex drive
b. aldosterone → increases sodium concentration in the blood
hig c. female hormones → promote long bone growth in adolescents
hb
loo d. Pairs b and c are correct.
dN
a+
e. All are correct.
11. Which hormone opposes the effect of aldosterone in the body?
Homeostasis (normal blood pressure)
a. renin c. atrial natriuretic hormone
low b. angiotensin I d. cortisol
blo
od 12. Aldosterone returns blood pressure to normal by causing the
Na +
kidneys to reabsorb water and sodium. As you know, it works
by negative feedback. Give an example from your daily life
during which your adrenal cortex produces aldosterone.
Blood pressure Answers in Appendix A.
rises.
10.5 Pancreas
Kidneys secrete 13. Describe the anatomy of the pancreas.
renin into blood. 14. Name three hormones produced by the pancreas, and discuss their
functions.
15. Discuss the two types of diabetes mellitus, and contrast hypoglyce-
Kidneys mia with hyperglycemia.
reabsorb Na+ renin
and water from
kidney tubules.
The pancreas is a long organ that lies transversely in the abdomen
just inferior to the stomach. Its widest portion, called the head, is
located immediately lateral to the duodenum of the small intestine.
angiotensin It is composed of two types of tissue. Exocrine tissue produces and
aldosterone I and II
secretes digestive juices that travel through ducts to the small intes-
Adrenal cortex tine. Pancreatic endocrine tissue includes three types of hormone-
secretes producing cells, found in clusters called the pancreatic islets
aldosterone
into blood.
(islets of Langerhans). Pancreatic alpha cells produce glucagon,
beta cells produce insulin, and delta cells produce somatostatin.
Figure 10.11 Regulation of blood pressure and volume. All three hormones are released directly into the blood.
Bottom: When the blood sodium (Na1) level is low, low blood pres- The two antagonistic hormones, insulin and glucagon, both
sure causes the kidneys to secrete renin. Renin leads to the secre- produced by the pancreas, help maintain the normal level of blood
tion of aldosterone from the adrenal cortex. Aldosterone causes the glucose. Insulin is secreted when the blood glucose level is high,
kidneys to reabsorb Na1, and water follows, so that blood volume which usually occurs just after eating. Insulin stimulates the up-
and pressure return to normal. Top: When the blood Na1 is high, a take of glucose by most body cells. Insulin is not necessary for
high blood volume causes the heart to secrete atrial natriuretic hor-
glucose transport into brain or red blood cells, but muscle cells
mone (ANH). ANH causes the kidneys to excrete Na1, and water
and adipose tissue cells require insulin for glucose transport. In
follows. The blood volume and pressure return to normal.
liver and muscle cells, insulin stimulates enzymes that promote the
Figure 10.12 Addison’s disease. Addison’s disease is characterized by a peculiar bronzing of the skin, particularly noticeable in these
light-skinned individuals. Note the color of (a) the face and (b) the hands compared to the hand of an individual without the disease.
a. b.
storage of glucose as glycogen. In muscle cells, the glucose sup- Diabetes Mellitus
plies energy for muscle contraction, and in fat cells, glucose enters
Diabetes mellitus is a fairly common hormonal disease in which
the metabolic pool and thereby supplies glycerol for the formation
insulin-sensitive body cells are unable to take up and/or metabolize glu-
of fat. In these ways, insulin lowers the blood glucose level.
cose. Therefore, the blood glucose level is elevated—a condition called
Glucagon is secreted from the pancreas, usually between
hyperglycemia. Because body cells cannot access glucose, starvation
meals, when the blood glucose level is low. The major target
occurs at the cell level. The person becomes extremely hungry—a con-
tissues of glucagon are the liver and adipose tissue. Glucagon
dition called polyphagia. As the blood glucose level rises, glucose will
stimulates the liver to break down glycogen to glucose and to
be lost in the urine (glycosuria). Glucose in the urine causes exces-
use fat and protein in preference to glucose as energy sources.
sive water loss through urination (polyuria). The loss of water in this
Adipose tissue cells break down fat to glycerol and fatty acids.
way causes the diabetic to be extremely thirsty (polydipsia). Because
The liver takes these up and uses them as substrates for glucose
glucose is not being metabolized, the body turns to the breakdown of
formation. In these ways, glucagon raises the blood glucose level
protein and fat for energy. Fat metabolism leads to the ketone buildup
(Fig. 10.14).
in the blood, and ketone excretion in the urine (ketonuria). Ketones
Somatostatin prevents the release of the other two hormones.
are acidic, so their buildup in blood causes acidosis, or acid blood. This
In this way, it prevents wide swings in blood sugar that might occur
condition, called ketoacidosis, can lead to coma and death.
between meals.
If you’re someone with diabetes mellitus, the disorder involving the If the blood glucose isn’t too low, the insulin shock can be corrected at
hormone insulin, you already know the importance of maintaining a home. However, one should never attempt to give food or drinks to
stable blood glucose level to ensure your long-term health. If your room- someone who is semiconscious or unconscious—she could easily
mate, friend, or loved one is a diabetic, you need to be informed, too, choke. Instead, the inside of her cheeks can be smeared with glucose gel,
because a diabetic’s possible problems don’t always take a long time to honey, syrup, or frosting, which will melt and be swallowed. If the
develop. Insulin shock and diabetic ketoacidosis (DKA) can develop patient doesn’t quickly become alert enough to eat or drink, she must be
very rapidly, and both can be fatal or result in permanent brain damage. transported to an emergency room. There, an injection of glucagon or an
It’s important for diabetics and their friends and family to recognize the intravenous solution will quickly raise the blood glucose level.
symptoms of insulin shock and DKA, and know how to use a glucome- Diabetic ketoacidosis is caused by blood glucose that is too high.
ter to measure blood glucose and how to give an injection. It commonly results when the diabetic eats a meal, but forgets to inject
Insulin shock (also called an insulin reaction) results when blood insulin. Infection, injury, or extreme stress can also lead to DKA. The
glucose falls to critically low levels—a condition called hypoglycemia. symptoms of DKA are increased thirst, frequent urination, nausea, and
It often results when the diabetic patient accidentally injects too much vomiting. The patient breathes rapidly, and his breath smells like fruit-
insulin, or takes her insulin but misses a meal. The patient is likely to flavored gum. His pulse is very fast, but his blood pressure is low. With-
feel anxious, sweat profusely, and complain of a headache. She may out an identifying bracelet or tag, he could easily be mistaken as
become hyperactive, confused, and even psychotic as the condition someone who’s had too much to drink: sluggish, lethargic, and increas-
worsens. Eventually, she’ll lose consciousness and lapse into a so-called ingly sleepy. If untreated, he’ll eventually fall into a diabetic coma. For-
diabetic coma. tunately, under a physician’s direction, a trained paramedic can start an
It’s critical for first responders to try to raise the patient’s blood intravenous solution to help dilute the patient’s blood. As he is being
glucose as quickly as possible. If she is conscious and alert, she can transported to the emergency room, EMS personnel can then measure
quickly drink milk, juice, or soda, or eat something sweet. She may be the glucose and ketones in his blood to provide a complete history, in
able to self-inject with glucagon, the hormone that raises blood glucose. preparation for more complete treatment in the hospital.
“I can remember getting sick with the flu when I was 11. I missed two or in the future to transform the patient’s own stem cells into a new beta
three days of school, and I just never got my strength back. I ate and drank cell population using this process. If successful, such a technique
constantly because I was thirsty and hungry all the time. I was always in would completely eliminate the need for anti-rejection drugs and
the bathroom, and I started wetting the bed—can you imagine, at age 11? would make islet cell transplants much more commonplace.
I fell asleep in school, and the teacher could barely get me to wake up. Meanwhile, scientists continue to investigate ways to shield
That’s when my doctor diagnosed my diabetes for the first time.” transplanted cells from the recipient’s immune system, and thus,
The patient, age 25, is a typical type I insulin-dependent dia- reduce the risk of rejection. In previous studies of a technique called
betic. Her symptoms are characteristic of this form of diabetes microencapsulation, scientists placed beta cells into tiny, porous con-
mellitus (IDDM) (see pages 230–231). As you’ve read, in insulin- tainers consisting of minute carbon tubes called nanotubes. Early
dependent diabetes, the body’s own immune cells destroy pancre- results showed that the cells were initially able to survive and produce
atic beta cells. To treat their illness, type I diabetic patients inject insulin for a time. However, the cells quickly failed and died due to a
insulin three or more times daily or use a continuous insulin pump lack of oxygen and nutrients. Now, new microencapsulation studies
device. Patients use blood tests to check their blood glucose levels sponsored by the Diabetes Research Institute have led to techniques
throughout each day. Further, diabetics must carefully monitor their that enable beta cells to be individually enclosed in tight capsules, and
diets, activities, and stress levels, and regular exercise is also a must. then layered into a bioengineered scaffold called a BioHub. This tech-
Fortunately, ongoing research into diabetes therapy holds the nique enables oxygen and nutrients to reach the cells, and it allows the
promise of treatments that will be much safer and more effective. cells to respond to changes in blood sugar, as though they were housed
Recently, the results were reported from clinical studies on an artificial in a person’s body. If these studies are successful, human or pig beta
pancreas system (APS) that effectively combines two existing tech- cells could be transplanted, and patients would not need either anti-
nologies. The first is the insulin pump, a cell-phone-sized device that rejection medication or insulin injections (Fig. 10A).
continually injects insulin into the patient’s body through fine tubing While these long-term solutions are being researched, new ways
which the patient positions under the abdominal skin. The second to deliver insulin into the body are being developed. For example,
device is a continuous glucose monitor (CGM), which can constantly researchers are actively exploring insulin delivery options that are less
sample glucose levels in subcutaneous tissue fluid and give real-time painful, and potentially more effective and more reliable than injec-
information about the patient’s status. The new device, called Diabetes tions. Currently, diabetics can’t swallow their insulin in a pill, because
Assistant (DiAs) is a smartphone-based application that is wirelessly harsh stomach acid destroys the protein before it can be absorbed.
connected to both the patient’s CGM and insulin pump. In the study, Pharmaceutical companies continue in their efforts to develop gels that
each patient’s DiAs received real-time information from both devices, would reliably shield the insulin as it passes through the stomach while
then estimated the patient’s metabolic rate and adjusted the insulin allowing it to be absorbed in the intestine. Researchers are optimistic
delivery to maintain blood glucose in a normal range. Preliminary that some form of insulin pill might soon be available for use.
results were promising: the blood glucose levels of study participants
were maintained within normal levels, without the need for researchers
to intervene. When the APS is perfected, researchers hope it will
respond much as a real pancreas does: delivering just the right amount
of insulin at just the right moment, day in and day out.
Whole pancreatic transplant can be a permanent cure for indi-
vidual diabetics, but there is a shortage of donor organs. Further, the
transplant is major surgery, and recipients must take lifelong anti-
rejection medications, which have severe side effects (recurring
infections, increased cancer risk, kidney damage, etc.). While less
common, pancreatic islet cell transplantation also continues to show
some promise as a permanent cure for type I diabetes. With this
approach, cadaver beta cells are directly injected into the liver, where
they form colonies and produce insulin. Regrettably, as with whole
pancreas transplants, this type of transplant is limited by the scarcity
of donor cells and complicated by the ever-present risk of rejection.
However, in October 2014, researchers at Harvard University
announced the development of a technique to produce large quantities
of pancreatic beta cells from transformed embryonic stem cells. While
Figure 10 A Encapsulated insulin-producing pancreatic
islet cells from pigs can be transplanted into patients without
this is encouraging, there are practical and ethical issues that remain
the need for immune system–suppressing drugs.
regarding the use of embryonic stem cells. Perhaps it will be possible
They’re called “performance-enhancing steroids,” and allegations from both inside and outside the industry maintain that such abuse
of their use remain widespread in athletics, both amateur and pro- has been going on for many years, and that it continues despite the
fessional. Whether the sport is baseball, football, track and field negative publicity. Of tremendous concern to lawmakers, educators,
events, or professional cycling, no activity seems to be safe from and parents is the increased use of steroids by teens wishing to bulk
drug abuse. In January 2013, after years of repeated denials, Lance up quickly, perhaps seeking to be just like the sports figures they
Armstrong finally admitted to using testosterone during the years admire.
when he won an unprecedented seven Tour de France cycling races. Anabolic steroids are synthetic forms of the male sex hormone
Even the Olympic Games have been affected. Olympic history was testosterone. Taking doses 10 to 100 times the amount prescribed by
forever changed when Marion Jones, the first female athlete to win doctors for various illnesses promotes larger muscles when the per-
five medals for track and field events, admitted steroid abuse dur- son also exercises. Trainers may have been the first to acquire ana-
ing the 2000 Sydney Games. In 2008, she was stripped of all med- bolic steroids for weight lifters, bodybuilders, and other athletes,
als she had earned and disqualified from a fifth-place finish in the such as professional baseball players. However, being a steroid user
2004 Athens Games. Future Olympic record books will not include can have serious detrimental effects. Men often experience decreased
her name, and the records of her relay teammates have also been sperm counts and decreased sexual desire due to atrophy of the tes-
tainted. Baseball records will also likely require revisions. The ticles. Some develop an enlarged prostate gland or grow breasts. On
great 1998 home-run competition between Mark McGwire and the other hand, women can develop male sexual characteristics.
Sammy Sosa was largely credited with reviving national interest in They grow chest and facial hair, and lose scalp hair; many experi-
baseball. Both McGwire and Sosa were later accused of using ana- ence abnormal enlargement of the clitoris. Some women cease ovu-
bolic steroids, and in 2010, McGwire admitted that the allegations lating or menstruating, sometimes permanently. Researchers have
were true. Likewise, both Jose Canseco of the Oakland Athletics predicted that two or three months of high-dosage use of anabolic
and Jason Giambi of the New York Yankees have confessed to steroids as a teen can cause death by age 30 or 40. These drugs have
using performance-enhancing drugs. Similar charges of drug abuse even been linked to heart disease and sudden death in both sexes, and
may prevent baseball greats Roger Clemens and Barry Bonds from have been implicated in the deaths of young athletes from liver
ever entering the Baseball Hall of Fame, despite each player’s cancer and one type of kidney tumor. Steroids can cause the body to
award-winning career. retain fluid, which results in increased blood pressure. Users then try
Many athletes and officials continue to deny that anabolic ste- to get rid of “steroid bloat” by taking large doses of diuretics. A
roids are widely used in professional sports. However, many people young California weight lifter had a fatal heart attack after using
for the secondary sex characteristics in females, including female called thymosins. These hormones aid in the differentiation of
body hair and fat distribution. In general, females have a more lymphocytes packed inside the lobules. Although the hormones
rounded appearance than males because of a greater accumula- secreted by the thymus ordinarily work only in the thymus, re-
tion of fat beneath the skin. Also, the pelvic girdle is wider in searchers hope that these hormones could be injected into AIDS
females than in males, resulting in a larger pelvic cavity. Both or cancer patients where they would enhance T-lymphocyte
estrogen and progesterone are required for breast development function.
and for regulation of the uterine cycle, which includes monthly
menstrual periods (discharge of blood and mucosal tissues from Pineal Gland
the uterus). The pineal gland, which is located in the brain, produces the
hormone melatonin, primarily at night. Melatonin is involved
Thymus Gland in our daily sleep-wake cycle; normally we grow sleepy at night
The lobular thymus gland, which lies just beneath the sternum when melatonin levels increase and awaken once daylight re-
(see Fig. 10.1), reaches its largest size and is most active dur- turns and melatonin levels are low (Fig. 10.15). Daily 24-hour
ing childhood. It then shrinks in size throughout one’s adult cycles such as this are called circadian rhythms. Circadian
life. Lymphocytes are white blood cells that originate in the rhythms are controlled by an internal timing mechanism called
bone marrow and are responsible for specific defenses against a biological clock.
a particular invader. When lymphocytes mature and complete Based on animal research, it appears that melatonin also reg-
their development in the thymus, they are transformed into ulates sexual development. It has also been noted that children
thymus-derived lymphocytes, or T lymphocytes. The lobules whose pineal gland has been destroyed due to a brain tumor experi-
of the thymus are lined by epithelial cells that secrete hormones ence early puberty.
Content CHECK-UP!
16. Describe three functions of the female sex hormones.
Chemical Signals Between Individuals
17. Which of the following is a local tissue messenger that stimu- Chemical signals that act between individuals are called pheromones
lates nearby cells? (see the Introduction, Chapter 17). There are many examples of
a. leptin c. melatonin pheromones in other animals, but they may also be effective between
people. Humans produce airborne chemicals from a variety of areas,
b. prostaglandin d. thymosin
including the scalp, oral cavity, armpits, genital areas, and feet. For
18. From the following list of endocrine glands and their hor-
example, the armpit secretions of one woman could possibly affect
mones, choose the pair that is correct:
the menstrual cycle of another woman. Women who live in the same
a. ovaries → androgens c. kidney → aldosterone
household often have menstrual cycles during the same times of the
b. thymus → insulin d. adipose tissue → leptin month. Further, when women with irregular cycles are exposed to
Answers in Appendix A. extracts of male armpit secretions, their cycle length tends to become
more normal.
Nervous System
Urinary System
Hormones affect
development of brain. ADH, aldosterone, and
testes (male) atrial natriuretic hormone
Hypothalamus, pituitary, regulate reabsorption of
and pineal gland are part of water and Na + by kidneys.
endocrine system; nerves
innervate glands of secretion. Kidneys keep blood values
within normal limits so that
transport of hormones
continues.
Cardiovascular System
Study Questions
1. Explain how peptide hormones and 3. Explain the relationship of the hypo- hypothalamus, the anterior pituitary,
steroid hormones affect the metabo- thalamus to the posterior pituitary and other endocrine glands.
lism of the cell. (pp. 218–221) gland and to the anterior pituitary (pp. 222–224)
2. Contrast hormonal and neural signals, gland. List the hormones secreted by 5. Discuss the effect of growth hormone
and show that there is an overlap be- the posterior and anterior pituitary on the body and the result of having
tween the mode of operation of the glands. (pp. 219–220, 222–224) too much or too little growth hormone
nervous system and that of the endo- 4. Give an example of the negative when a young person is growing. What
crine system. (pp. 218–221) feedback relationship among the is the result if the anterior pituitary
PART IV
Blood
I f you know about ABO blood types, and know your own, maybe you’ve
wondered which of the four possible types is the most common worldwide.
The answer depends on the genetic inheritance of a particular population.
Worldwide, the most prevalent ABO type is type O. However, type A blood is
most common in several European countries, including the Scandinavian
countries. In certain geographic areas, virtually the entire population has the
same blood type. For example, certain native Central and South American
tribes are nearly all type O. The least common ABO type is type AB. If you also
know your Rh type (positive or negative), you’ll be interested to know that
approximately 85% of Caucasians, 92% of African Americans, and 97% of
Asians are Rh positive. In addition to the A, B, and Rh proteins, there are
several thousand known blood proteins that have been identified. The
International Society of Blood Transfusion has organized 32 separate major
group systems to classify them (ABO and Rh are two examples of group
systems). Doubtless, more proteins remain to be discovered, and more
classification systems will be developed for them. You can read more about
blood types and blood compatibility on pages 252–254.
Learning Outcomes After you have studied this chapter, you should be able to:
11.1 The Composition and Functions 11.3 Platelets and Hemostasis Visual Focus
of Blood 6. Describe the structure, function, and Hematopoiesis
1. Describe, in general, the composition life cycle of platelets.
of blood and define the term 7. Describe the three events of hemo Medical Focus
hematocrit. stasis and the reactions necessary Abnormal Red and White Blood Cell Counts
2. Divide the functions of blood into three for coagulation to occur.
categories, and discuss each category. 8. Discuss disorders of hemostasis. What’s New
Improvements in Transfusion Technology
11.2 Components of Blood 11.4 Blood Typing and Transfusions
3. Describe the composition of plasma, 9. Explain the ABO and Rh systems of I.C.E.—In Case of Emergency
and explain the functions of the blood typing.
plasma proteins. Hemorrhage
10. Explain agglutination and its
4. Explain the hematopoietic role of relationship to transfusions.
stem cells in the red bone marrow. Focus on Forensics
5. Describe the structure, function, and 11.5 Effects of Aging Blood at the Crime Scene
life cycle of red blood cells and white 11. Name the blood disorders that are
blood cells. Briefly outline the effects commonly seen as we age.
of abnormal red and white blood cell
counts.
242
eosinophil
Defense
platelets
Because blood contains the white blood cells, it defends the
monocyte body against invasion by pathogens (microscopic infectious
neutrophils
agents, such as disease-causing bacteria and viruses). The white
basophil blood cells also remove dead and dying cells, clearing room
lymphocyte for the growth of healthy cells. Mutated cells—which could
red blood
cell
potentially develop into cancer—are destroyed by white blood
cells as well. Certain white blood cells are capable of engulfing
b. 2503
and destroying pathogens or cancer cells; others produce and
Figure 11.1 Composition of blood. (a) When blood is secrete antibodies into the blood. Antibodies are proteins made
transferred to a test tube containing an anticoagulant (to by a specific class of white blood cells. They incapacitate patho-
prevent clotting) and then centrifuged, it consists of three layers. gens, making them subject to destruction by other white blood
The transparent strawcolored or yellow top layer is the plasma, cells. This function of the blood will be discussed completely
the liquid portion of blood. The thin middle buffy coat layer con in Chapter 13.
sists of leukocytes and platelets. The bottom layer contains the When an injury occurs, blood forms a clot, and this prevents
erythrocytes. (b) Micrograph of the formed elements in blood.
blood loss. Blood clotting involves platelets and the plasma pro-
Neutrophils, basophils, eosinophils, monocytes, and lympho
teins prothrombin and fibrinogen. Without blood clotting, we
cytes are all different forms of white blood cells.
could bleed to death even from a small cut.
Granular leukocytes
Spherical cells with bilobed
Inorganic ions Maintain blood osmotic Absorbed nuclei; coarse, deep-red,
(salts) pressure and pH; aid from uniformly sized granules
(less than 1% of metabolism intestine in cytoplasm; phagocytize
plasma)
antigen-antibody complexes
1–4% and allergens
Early differentiation
separates myeloid stem
cells from lymphoid
stem cells. multipotent
stem cells
myeloid lymphoid
stem cells stem cells
Myeloblasts, monoblasts,
and lymphoblasts produce
the white blood cells.
megakaryocytes
reticulocyte
B lymphocytes T lymphocytes NK
Platelets basophils eosinophils neutrophils processed in processed in cell
monocytes bone marrow thymus
erythrocytes
Granular leukocytes Agranular leukocytes
Figure 11.3 Hematopoiesis. Multipotent stem cells give rise to two specialized stem cells. The myeloid stem cell gives rise to
still other cells, which become red blood cells, platelets, and all the whole blood cells except lymphocytes. The lymphoid stem cell gives
rise to lymphoblasts, which become lymphocytes. Though they have granules like the granular leukocytes, natural killer cells also arise
from the lymphoid stem cells.
Normal blood
oxygen content
2. Kidneys increase
production of
erythropoietin
helical shape
of the
polypeptide
molecule
4. Blood oxygen
content returns
to normal
Normal erythrocyte count should be in the range of 4–6 million cells per survivors have children, the sickle-cell gene passes on to the next
cubic millimeter of blood (about the size of one large drop), and normal generation. In the United States, sickle-cell disease is most common
blood hemoglobin level is 12–17 grams per 100 milliliters. However, it’s in African Americans whose ancestors are from equatorial Africa, but
important to recognize gender variation: due to the effects of androgen it occurs in people of any race.
hormones such as testosterone, men have a higher red blood cell count Dietary anemias occur because the patient’s diet lacks substances
(and thus, a higher hemoglobin level) than women. Various disease needed for red blood cell development. In iron deficiency anemia, a
processes can affect erythrocyte count and hemoglobin levels. As you common type of anemia, the person’s diet does not contain enough iron,
know from the Begin Thinking Clinically question on page 247, polycy- or there is excessive iron loss from the body. The hemoglobin count is
themia is a disorder in which an excessive number of red blood cells low, red blood cells are small and pale in color, and the individual feels
makes the blood so thick that it is unable to flow properly. An increased tired and run-down. Including iron supplements in the diet can help pre-
risk of clot formation is also associated with this condition. vent this type of anemia. Pernicious anemia is another form of dietary
In anemia, the number of red cells is insufficient and/or the cells anemia. The digestive tract is unable to absorb enough vitamin B12, which
do not have enough normal hemoglobin. Anemia can be classified is essential to red cell development. Without vitamin B12, immature red
into one of several categories. The first category, hemolytic anemia, cells tend to accumulate in the bone marrow. A special diet, vitamin sup-
occurs because the rate of red blood cell destruction increases (hemo- plements, and/or injections of vitamin B12 are effective treatments.
lysis is the rupturing of red blood cells). Hemolytic disease of the In aplastic anemia, the red bone marrow has been damaged due
newborn, discussed at the end of this chapter (see page 253), is one to radiation or chemicals, and red blood cells, white blood cells, and
form of this type of anemia. platelets are all deficient. Bone marrow transplant is one option to
Sickle-cell disease is an inherited hemolytic anemia caused by an treat this condition.
abnormal form of hemoglobin. Affected individuals have fragile, sickle- Hemorrhagic anemia is decreased red blood cell count follow-
shaped red blood cells (a sickle is a shape resembling the letter C; ing a hemorrhage. Transfusions may be administered to increase red
Fig. 11A) that easily tear open as they pass through the narrow capillaries. blood cell count. Research continues to develop improvements in
As a result, the person has far fewer red blood cells than normal, and transfusion technology, as detailed in What’s New on page 255.
anemia symptoms result. Both parents must carry the gene for sickle-cell Certain viral illnesses, such as influenza, measles, and mumps,
disease for a child to be afflicted. Someone with a single gene is said to cause the white blood cell count to decrease. Leukopenia is a total
have sickle-cell trait, and doesn’t have disease symptoms. white blood cell count below 5,000 per cubic millimeter. Other ill-
Both sickle-cell disease and sickle-cell trait are most prevalent nesses, including appendicitis and bacterial infections, cause the
among people who live in areas bordering the equator (for example, in white blood cell count to increase dramatically. Leukocytosis is a
Africa, Asia, India, and Central and South America) where malaria is white blood cell count above 10,000 per cubic millimeter.
common. Malaria is a disease caused by a parasite and spread by Illness often causes an increase in a particular type of white blood
mosquitoes that infect humans when they bite. Having sickle-cell trait cell. For this reason, a differential white blood cell count may help
gives the person a better chance of surviving malaria, though it doesn’t with diagnosis. In this microscopic procedure, 100 white blood cells are
protect against the actual infection or subsequent illness. Scientists counted, and numbers of each type of cell are recorded. For example,
aren’t sure why the trait enables some people to survive, but when the characteristic finding in the viral disease mononucleosis is a great
number of large, dark-staining abnormal lymphocytes. This condition
takes its name from the fact that the abnormal lymphocytes resemble
monocytes (although monocytes are much larger than lymphocytes).
Leukemia is a form of cancer characterized by uncontrolled pro-
duction of abnormal white blood cells. These cells accumulate in the
bone marrow, lymph nodes, spleen, and liver so that these organs are
unable to function properly. Acute lymphoblastic leukemia (ALL),
which represents over 80% of the acute leukemias in children, also
occurs in adults. Chemotherapy is used to destroy abnormal cells and
restore normal blood cell production. Intraspinal injection of drugs and
craniospinal irradiation are measures that prevent leukemic cells from
invading the central nervous system. In general, the prognosis is more
favorable for children between the ages of 2 and 10 years, and females
fare better because leukemia recurs in the testes of 8–16% of males.
Remission occurs in 70–90% of adult patients after chemotherapy, and
the median period of remission is 20 months. With chemotherapy, 85%
Figure 11A Sickle-shaped red blood cells, as seen by a
of children survive past five years, and of those among this group who
scanning electron microscope.
do not have a relapse, 85% are considered cured.
2
prothrombin
11.3 Platelets and Hemostasis activator
Ca2+ fibrinogen
Anyone who drives a car might be involved in a minor fender-bender Experts agree that the best way to stop a hemorrhage is to
type of accident. Thankfully, in those situations only the car gets “hurt.” quickly apply direct pressure to the injury site, using gauze, towels,
However, as you know, a car can be a deadly piece of equipment. Car clothing, or even your bare hand if you must. Not only does pressing
accidents are the leading cause of death for people ages 16–26, and the on a bleeding wound stop or slow the bleeding, it will also start the
fifth-leading cause of death overall, according to the Centers for Disease blood clotting process. If the cloth becomes soaked, don’t remove it;
Control (CDC). Tragically, many of these deaths are caused by severe add more layers. A clot may have begun to form in the fabric, and
bleeding, or hemorrhage, and might have been prevented. peeling it away might cause bleeding to start again. In addition, ele-
When you’re the first person at an accident scene, your help could vate the victim’s legs, and keep him or her warm. Taking these steps
make the difference between life or death for a hemorrhaging patient. will help prevent shock.
It’s important to react appropriately—first get yourself and the victim At the accident scene, EMS providers can begin an IV while
out of danger, and then call for assistance. Next, immediately check the transporting the patient to the emergency room. In addition, paramedic
patient’s ABCs: Airway—ensure that the airway is intact and open; crews, hospital emergency rooms, and military medics now carry pre-
Breathing—observe regular respiration; and Circulation—check for pared dressings that are designed to stop bleeding, even in deep
heartbeat and pulse. Once you’ve taken these steps, act quickly to stop wounds. All work by quickly drawing water out of blood plasma, con-
or slow any serious bleeding. Excessive blood loss can cause blood centrating the clotting factors at the site of the wound. This promotes
pressure to fall, a condition called hypovolemic shock. Shock causes rapid clot formation, sometimes stopping even a severe hemorrhage
organ failure and death if not treated. within minutes.
11.4 Blood Typing and Transfusions with the other ABO blood types, a person with type AB blood has
neither anti-A nor anti-B antibodies in the plasma.
9. Explain the ABO and Rh systems of blood typing.
Blood compatibility is very important when transfusions are
10. Explain agglutination and its relationship to transfusions.
done. The antibodies in the plasma must not combine with the
antigens on the surface of the red blood cells, or else agglutination
A blood transfusion is the transfer of blood from one individ- occurs. With agglutination, anti-A antibodies have combined with
ual into the blood of another. In order for transfusions to be done type A antigens, or anti-B antibodies have combined with type B
safely, it is necessary for blood to be typed so that agglutination antigens, or both types of binding have occurred. Therefore, agglu-
(clumping of red blood cells) does not occur. Blood typing usually tination is expected if the donor has type A blood and the recipient
involves determining the ABO blood group and whether the indi- has type B blood (Fig. 11.9). What about other combinations of
vidual is Rh2 (negative) or Rh1 (positive). blood types? Table 11.1 shows when a blood transfusion is most
likely safe. Type O blood is sometimes called the universal donor
ABO Blood Groups because it has no antigens on the red blood cells, and type AB blood
is sometimes called the universal recipient because this blood type
ABO blood typing is based on the presence or absence of two pos-
has no antibodies in the plasma. In practice, however, there are
sible antigens, called type A antigen and type B antigen, on the
other possible blood groups, aside from ABO blood groups, so it
surface of red blood cells. Whether these antigens are present or
is necessary to physically put the donor’s blood on a slide with the
not depends on the particular inheritance of the individual.
recipient’s blood and observe whether the blood types match (no
A person with type A antigen on the surface of the red blood cells
has type A blood; one with type B blood has type B antigen on the
surface of the red blood cells. What antigens would be present on the
surface of red blood cells if the person has type AB blood or type O
TABLE 11.1 Transfusion
blood? Notice in Figure 11.8 that a person with type AB blood has both If your blood type is: You can safely receive
antigens. A person with type O blood has no AB antigens on the sur- blood of this type*
face of the red blood cell, though other protein antigens will be present.
A A or O
It so happens that an individual with type A blood has anti-B anti-
B B or O
bodies in the plasma; a person with type B blood has anti-A antibodies
AB A, B, AB, or O
in the plasma; and a person with type O blood has both antibodies in
O O
the plasma (Fig. 11.8). These antibodies are not present at birth, but
*Regardless of ABO type, a person who is Rh2 can never be transfused with Rh1 blood.
they appear over the course of several months after birth. Unlike those
Type A blood. Red blood cells have type A surface antigens. Type AB blood. Red blood cells have type A and type B surface
Plasma has anti-B antibodies. antigens. Plasma has neither anti-A nor anti-B antibodies.
type B antigen
Type B blood. Red blood cells have type B surface antigens. Type O blood. Red blood cells have neither type A nor type B
Plasma has anti-A antibodies. surface antigens. Plasma has both anti-A and anti-B antibodies.
Figure 11.8 Types of blood. In the ABO system, blood type depends on the presence or absence of antigens A and B on the surface
of red blood cells. In these drawings, A and B antigens are represented by different shapes on the red blood cells. The possible antiA and
antiB antibodies in the plasma are shown for each blood type. Notice that an antiB antibody cannot bind to an A antigen, and vice versa.
agglutination occurs) before blood can be safely given from one If a mother is Rh2 and the father is Rh1, the fetus conceived
person to another. This is called cross-matching blood. can be Rh1. The Rh1 red blood cells may begin leaking across
As explained in the What’s New reading on page 255, new the placenta into the mother’s cardiovascular system, as placental
technology may help to eliminate the problems of matching tissues normally break down before and at birth. The presence
blood types. of these Rh1 antigens causes the mother to produce anti-Rh
antibodies. During this pregnancy or a subsequent pregnancy with
another Rh1 baby, the anti-Rh antibodies may cross the placenta
Rh Blood Groups and destroy the child’s red blood cells. This is called hemolytic
The designation of blood type usually also includes whether the disease of the newborn (HDN) because hemolysis continues after
person has or does not have the Rh factor on the red blood cell. the baby is born (Fig. 11.10). Due to red blood cell destruction the
Rh2 individuals normally do not have antibodies to the Rh factor, baby can be severely anemic at birth. Excess bilirubin in the blood
but they make them when exposed to the Rh factor. can lead to brain damage and developmental delay, or even death.
Child is Rh positive; Red blood cells leak Mother makes anti-Rh Antibodies attack Rh-positive
mother is Rh negative. across placenta. antibodies. red blood cells in child.
Figure 11.10 Hemolytic disease of the newborn. Due to a pregnancy in which the child is Rh positive, an Rhnegative mother can
begin to produce antibodies against Rhpositive red blood cells. In a subsequent pregnancy, these antibodies can cross the placenta and
cause hemolysis of an Rhpositive child’s red blood cells.
The Rh problem is prevented by giving Rh2 women an Rh immu- 11.5 Effects of Aging
noglobulin injection at 28 weeks of pregnancy, followed by a second
11. Name the blood disorders that are commonly seen as we age.
injection no later than 72 hours after giving birth to an Rh1 child. This
injection, called Rho-Gam, contains anti-Rh antibodies that attack any
of the baby’s red blood cells in the mother’s blood before these cells Anemias, leukemias, and clotting disorders increase in frequency
can stimulate her immune system to produce her own antibodies. This with age. As with other disorders, good health habits can help pre-
injection is not beneficial if the woman has already begun to produce vent these conditions from appearing.
antibodies; therefore, the timing of the injection is extremely important. Iron deficiency anemia most frequently results from an iron-
deficient diet, but it can also result from a gradual and sometimes
undetectable loss of blood. It is vital that the bleeding source be
Content CHECK-UP! discovered as soon as possible. For example, iron deficiency anemia
is often a first symptom of colon cancer in its early stage. The blood
10. Which of the following correctly describes type AB blood? is often not visible in a person’s stool because it has oxidized and is
a. A antigen and B antigen on the red cell membrane, antiA concealed in the stool. An occult blood test (test for oxidized blood
and antiB antibodies in plasma present in the stool) can detect this source of blood loss.
b. A antigen and B antigen on the red cell membrane, no Pernicious anemia most often signals that the digestive tract is
antibodies in plasma unable to absorb enough vitamin B12, but it can also be due to a diet
c. A antigen on the red cell membrane, antiB antibodies in deficient in B12. Diets that completely exclude animal-derived protein
plasma sources (called vegan diets) are often B12 deficient. A vitamin supple-
d. B antigen on the red cell membrane, antiA antibodies in ment containing B12 will prevent pernicious anemia in vegan dieters.
plasma Leukemia is a form of cancer that generally increases in fre-
11. Which of the following transfusions would most likely be safe quency with age because of both intrinsic (genetic) and extrinsic
to administer? (environmental) reasons.
a. type A blood to a type B blood recipient
Thromboembolism, a clotting disorder, may be associated
with the progressive development of atherosclerosis in an elderly
b. type AB blood to a type B blood recipient
person. When arteries develop plaque (see Fig. 12A), thromboem-
c. type B blood to a type AB recipient bolism often follows. For many people, atherosclerosis can be con-
d. type AB blood to a type O recipient trolled by diet and exercise, as discussed in the Chapter 12 Medical
12. Hemolytic disease of the newborn occurs in which situation? Focus, “Preventing Cardiovascular Disease.”
a. Rh1 mother, Rh2 father, Rh1 fetus
b. Rh2 mother, Rh2 father, Rh1 fetus Content CHECK-UP!
2 1 1
c. Rh mother, Rh father, Rh fetus 13. Elderly people often have poor appetites and don’t eat well.
d. Rh1 mother, Rh2 father, Rh2 fetus How can this cause anemia?
Answers in Appendix A. Answer in Appendix A.
If you work in an emergency room (ER) setting, having a supply of Unlike fibroblasts, iPSCs are capable of converting into hematopoietic
donor blood available for transfusion is a problem that you and your cells. After a month of growth in an environment similar to that of
co-workers will face every day. Your patient may be a victim of a car bone marrow, the iPSCs produced red blood cells that were then har-
accident, a shooting, or a stabbing. Perhaps she’s a pregnant woman vested from the cell culture. Because the fibroblasts had been obtained
who is hemorrhaging, or a leukemia sufferer whose hematocrit from an O-negative donor, all of the red blood cells were universal
(see page 243) has dropped dangerously low because of chemotherapy. donor cells and could therefore be transfused into anyone, regardless of
Without an immediate blood transfusion, the patient’s tissue cells will A-B-O or Rh blood type. The researchers are optimistic that this
die from lack of oxygen. If the ER is a major trauma center in a large technique can be applied to large-scale manufacturing. If that’s
city hospital, donor blood for transfusion is usually available, and the possible, it would lead to a steady, reliable, infection-free supply of
ready supply of O-negative blood can theoretically be donated universal donor red blood cells.
to anyone. In the meantime, research continues to explore ways of
But what if the transfusion is needed in a remote area where chemically altering red blood cell membranes. Once again, the goal is
whole blood isn’t available, such as a wartime field hospital or an to find a way to convert all donated blood to O-negative universal
accident scene on an isolated stretch of highway? Likewise, small donor blood, making it safe for anyone needing a transfusion. One
regional hospitals face regular shortages of donor blood. In an strategy involves antigen camouflage, in which the cell membrane
emergency (for example, a hemorrhaging patient), the patient can proteins are covered with a plastic-like “coat.” Once coated, the pro-
be transfused with plasma if whole blood is not available. How- teins can’t trigger a transfusion reaction in the recipient. A second
ever, plasma shortages are possible as well, especially in a mass procedure uses bacterial-derived enzymes to “scrub” the red blood
casualty situation. Further, although the majority of transfusions cells of A, B, and Rh antigens, essentially converting every donated
are safe, there is always a small chance of a transfusion reaction, unit into O-negative blood. Treated cells are called Enzyme Con-
in which the recipient’s immune system rejects the donor blood. verted group O (ECO) cells, and blood containing these cells has
Moreover, even though blood is carefully tested for viruses and already been safely transfused. Similarly, the problem of blood
other infectious agents, infection from donated blood is still a very plasma shortage is being addressed by a company developing tech-
slight possibility. niques to spray-dry blood plasma. Once dry, the plasma can be safely
Recent developments show promise in combating the problems stored without refrigeration for long periods of time, then dissolved in
of blood availability and safety by providing a constant supply of sterile solution to create plasma for transfusion.
O-negative universal donor cells. Scientists at the University of Whenever possible, surgeons avoid human-to-human blood
Edinburgh have successfully produced red blood cells from stem cells. transfusion entirely by using the patient’s own blood during an
These stem cells, called fibroblasts, were obtained from an adult donor. operation. This procedure is called autologous transfusion or
(Fibroblasts are described in Chapter 4.) The fibroblasts were then autotransfusion. For example, patients can have plasma or whole
“de-differentiated”—coaxed into becoming more primitive versions of blood stored before an elective surgery such as a hip replacement.
themselves—to create induced pluripotent stem cells (iPSCs). Then the patient receives a transfusion using his or her own blood
if needed. Intraoperative blood salvage, using an apparatus called
a “Cell Saver,” allows an emergency room physician or surgeon to
suction blood from the patient’s body. The suctioned blood is
immediately mixed with an anticoagulant, washed with a saline
solution to remove any contaminants, mixed with more saline, and
then reintroduced into a vein just like a traditional transfusion. The
procedure is quite fast: To prepare an entire unit of blood for rein-
fusion into the patient takes only three minutes. In addition, auto-
LM 2503
transfusion completely eliminates the possibility of transfusion
Erythrocytes reaction.
Until blood replacement technologies are perfected, there will
Figure 11B Erythrocytes passing through a capillary. always be a critical need for blood donation. To find out how you can
The cells line up in a single file to travel through these tiny
help, visit the Red Cross blood donor website at http://www.redcross
vessels.
.org/donate/give.
Summary
11.1 The Composition and Functions of C. Red blood cells are small, bicon neutrophils die within a few days
Blood cave disks that lack a nucleus. when they are fighting an infec
A. Blood, which is composed of Men have more RBCs than tion. Natural killer (NK) cells are
formed elements and plasma, has women because of the effects of granulocytes structurally similar to
several functions. It transports androgens such as testosterone. lymphocytes which help to de
hormones, oxygen, and nutrients Red blood cells contain hemo stroy damaged body cells. The
to the cells and carbon dioxide globin, the respiratory pigment, agranulocytes include the lym
and other wastes away from the which combines with oxygen and phocytes and the monocytes,
cells. It fights infections. It regu transports it to the tissues. Red which function in specific immu
lates body temperature, and blood cells live about 120 days nity. On occasion, the monocytes
keeps the pH of body fluids within and are destroyed in the liver become large phagocytic cells of
normal limits. All of these func and spleen when they are old or great significance. They engulf
tions help maintain homeostasis. abnormal. The production of red wornout red blood cells and
11.2 Components of Blood blood cells is controlled by the pathogens at a ferocious rate.
A. Plasma is mostly water (92%) and oxygen concentration of the 11.3 Platelets and Hemostasis
solutes (8%). Small organic blood. When the oxygen A. The extremely plentiful platelets
molecules such as glucose and concentration decreases, the result from fragmentation of
amino acids are dissolved in kidneys increase their produc megakaryocytes.
plasma and serve as nutrients for tion of erythropoietin, and more B. The three events of hemostasis
cells; urea is a waste product. red blood cells are produced. are vascular spasm, platelet plug
Large organic molecules include D. White blood cells are larger than formation, and coagulation. Extrin
the plasma proteins. The plasma red blood cells, have a nucleus, sic and intrinsic pathways that acti
proteins, most of which are pro and are translucent unless vate the clotting mechanism both
duced by the liver, occur in three stained. Like red blood cells, they cause formation of prothrombin
categories: albumins, globulins, are produced in the red bone activator, which breaks down pro
and fibrinogen. The plasma pro marrow. White blood cells are di thrombin to thrombin. Thrombin
teins maintain osmotic pressure, vided into the granular leukocytes changes fibrinogen to fibrin
help regulate pH, and transport and the agranular leukocytes. The threads, entrapping cells. The fluid
molecules. Certain plasma pro granular leukocytes have con that escapes from a clot is called
teins have specific functions: The spicuous granules; in eosinophils, serum and consists of plasma mi
gamma globulins, which are anti granules are red when stained nus fibrinogen and prothrombin.
bodies produced by B lympho with eosin, and in basophils, gran 11.4 Blood Typing and Transfusions
cytes, function in immunity; ules are blue when stained with a A. ABO typing is the most common
fibrinogen and prothrombin are basic dye. In neutrophils, some of blood typing system used. Type
necessary to blood clotting. the granules take up eosin, and A, type B, both type A and B, or
B. All blood cells, including red others take up the basic dye, giv no antigens can be on the surface
blood cells, are produced within ing them a lilac color. Neutrophils of red blood cells. In the plasma,
red bone marrow from stem cells, are the most plentiful of the white there are two possible antibodies:
which are constantly capable of blood cells, and they are able to antiA or antiB. If the correspond
dividing and producing new cells. phagocytize pathogens. Many ing antigen and antibody are put
Study Questions
1. Name the two main components of of red blood cells is regulated. red blood cells and the antibody(ies)
blood, and describe the functions of (pp. 247–248) in the plasma. (pp. 252–253)
blood. (pp. 243–244) 5. Name the six types of white blood 8. Explain why a person with type O
2. List and discuss the major components cells. Describe the structure and give a blood cannot receive a transfusion of
of plasma. Name several plasma pro function for each type. (pp. 248, 250) type A blood. (pp. 252–253)
teins, and give a function for each. 6. Name the steps that take place when 9. Problems can arise if the mother is
(pp. 244–245) blood clots. Which substances are pres which Rh type and the father is which
3. What is hemoglobin, and how does it ent in blood at all times, and which appear Rh type? Explain why this is so.
function? (pp. 246–247) during the clotting process? (pp. 250–251) (pp. 253254)
4. Describe the life cycle of red blood 7. What are the four ABO blood types?
cells, and tell how the production For each, state the antigen(s) on the
259
hepatic
12.1 Anatomy of the Heart vein arteries supplying
blood to digestive organs
1. Describe the location of the heart and its functions. liver digestive
hepatic tract
2. Detail the wall and coverings of the heart. portal renal artery
vein
3. Trace the path of blood through the heart, naming its chambers and renal vein common
valves. common iliac artery
kidneys
4. Explain the operation of the heart valves. iliac vein
internal internal
5. Outline the coronary circulation, and discuss several coronary circu- iliac artery
iliac vein
lation disorders and possible treatments.
capillaries
external external
The heart is located in the thoracic cavity within the mediasti- iliac vein
CO2 O2
iliac artery
pelvic organs
num, a serous membrane sac between the lungs. It is a hollow,
cone-shaped, muscular organ. To approximate the size of your
heart, make a fist and then clasp the fist with your opposite hand.
capillaries
Figure 12.1 shows that the base (the widest part) of the heart is
superior to its apex (the pointed tip), which rests on the diaphragm. CO2 O2
Also, the heart lies on a slant; the base is directed toward the right lower limbs
shoulder, and the apex points to the left hip. The base is deep to the
Figure 12.1 Cardiovascular system. The right side of
second rib, and the apex is at the level of the fifth intercostal space the heart pumps blood through vessels of the pulmonary circuit.
(though these positions can vary depending on a person’s size). The left side of the heart pumps blood through vessels of the
As the heart pumps the blood through the pulmonary and sys- systemic circuit. Gas exchange and nutrient-for-waste exchange
temic vessels, it performs these functions: occur as blood passes through lung (pulmonary) capillaries and
tissue (systemic) capillaries. In this illustration, red vessels carry
1. keeps oxygenated blood separate from partially deoxygen-
O2-rich blood, and blue vessels carry O2-poor blood.
ated blood;
heart wall
The Wall and Coverings of the Heart A layer of the heart can become inflamed due to infection,
cancer, injury, or a complication of surgery. The suffix “itis” added
The heart is composed of three layers, as shown in Figure 12.2. The
to the name of a heart condition tells which layer is affected. For
innermost layer, the endocardium, is a single layer of simple squa-
example, pericarditis refers to inflammation of the pericardium,
mous epithelium, called endothelium. Endothelium not only lines
and endocarditis refers to inflammation of the endocardium.
the heart but it also continues into and lines the blood vessels. Its
smooth nature helps prevent blood from clotting unnecessarily. The
central myocardium is the thickest part of the heart wall and is made Chambers of the Heart
up of cardiac muscle (see Fig. 4.15). When cardiac muscle fibers con- The heart has four hollow chambers: two superior atria (sing.,
tract, the heart beats. The outermost layer is the epicardium, which atrium) and two inferior ventricles (Fig. 12.3). Each atrium has
is also called the visceral serous pericardium (the term visceral an anterior pocket-like flap called an auricle. The auricles expand
means organ, and refers to the fact that this layer covers the heart). fully when the atrium fills with blood. Auricles also contain cells
After covering the heart, the visceral pericardium folds back over the that produce atrial natriuretic hormone (see p. 228), as well as car-
heart, creating the parietal serous pericardium. The two serous mem- diac stem cells. Internally, the atria are separated by the interatrial
branes (epicardium and parietal pericardium) secrete pericardial fluid septum, and the ventricles are separated by the interventricular
(a fluid similar to plasma). The pericardial fluid reduces friction as septum (plural, septa). Therefore, the heart’s pulmonary circuit (its
the heart beats. The parietal pericardium is fused to the outermost fi- right side) is completely separated from its systemic circuit (the
brous pericardium. The fibrous pericardium is a thick layer of fibrous left side) by the septa. However, it’s important to note that though
connective tissue that adheres to the great blood vessels at the heart’s they are physically separated, the pulmonary and systemic circuits
base and anchors the heart to the diaphragm and the mediastinal wall. perform their work together. Thus, the two atria contract simultane-
The coverings of the heart protect the heart, confine it to its location, ously, and then the two ventricles contract simultaneously.
and prevent it from overfilling, while still allowing the heart to con- The thickness of each chamber’s myocardium is suited to its
tract and carry out its function of pumping the blood. function. The atria have thin walls, and each pumps blood into the
pulmonary trunk
left pulmonary veins
right pulmonary artery
pulmonary
semilunar valve
left atrium b.
right atrium
atrioventricular
(bicuspid) valve
atrioventricular
(tricuspid) valve
chordae tendineae
ventricle below. The ventricles are thicker, and they pump blood Blood from the right ventricle passes through a semilunar
into blood vessels that travel to other parts of the body. The thinner valve into the pulmonary trunk. Semilunar valves are so called
myocardium of the right ventricle is suited for pumping blood to the because their cusps are thought to resemble half-moons. This par-
lungs, which are nearby in the thoracic cavity. The left ventricle has ticular semilunar valve, called the pulmonary semilunar valve,
a thicker wall than the right ventricle. Thicker myocardium enables prevents blood from flowing back into the right ventricle.
the left ventricle to pump its blood to all other parts of the body. Note in Figure 12.3 that the pulmonary trunk divides into the
left and right pulmonary arteries. For help in remembering how
Right Atrium blood flows through the heart, trace the path of O2-poor blood from
At its posterior wall, the right atrium receives O2-poor blood from the vena cava to the pulmonary arteries that take blood to the lungs
three veins: the superior vena cava, the coronary sinus, and the in- (see Fig. 12.1).
ferior vena cava. Venous blood passes from the right atrium into the
right ventricle through an atrioventricular (AV) valve. This valve, In the Lungs
like the other heart valves, directs the flow of blood and prevents Within the right and left lungs, the pulmonary arteries divide to form
any backflow. The AV valve on the right side of the heart is specifi- smaller and smaller arterioles. The smallest arterioles supply pulmo-
cally called the tricuspid valve because it has three cusps, or flaps. nary capillaries: tiny blood vessels which cover the alveoli, or air
sacs of the lungs. As you know from Chapter 4, both capillaries and
Right Ventricle alveoli are composed of simple squamous epithelium, an exceed-
In the right ventricle, the cusps of the tricuspid valve are con- ingly thin tissue. The respiratory gases oxygen and carbon dioxide
nected to fibrous cords, called the chordae tendineae (meaning freely diffuse between the alveoli and pulmonary capillaries. The
“heart strings”). The chordae tendineae in turn are connected to the capillaries then empty into pulmonary venules, which join to form
papillary muscles, which are conical extensions of the myocardium. larger veins. The largest of these veins are the four pulmonary veins.
left ventricle
right ventricle
apex
12.2 Physiology of the Heart Without this conduction system, the atria and ventricles would
contract at different rates.
6. Describe the conduction system of the heart.
7. Label and explain a normal electrocardiogram.
8. Describe the cardiac cycle and the heart sounds. Nodal Tissue
9. Describe the cardiac output and regulation of the heartbeat. The heartbeat is controlled by nodal tissue, which has both muscu-
lar and nervous characteristics. This unique type of cardiac muscle
The physiology of the heart pertains to its pumping action—that is, is located in two regions of the heart: The SA (sinoatrial) node
the heartbeat. It is estimated that the heart beats almost three billion is located in the upper posterior wall of the right atrium. The AV
times in a lifetime, continuously recycling some 5 to 6 liters (L) of (atrioventricular) node is located in the base of the right atrium
blood to keep us alive. In this section, we will consider what causes very near the interatrial septum (Fig. 12.5).
the heartbeat, what it consists of, and its consequences. The SA node initiates the heartbeat and automatically sends
out an excitation signal every 0.85 second. The SA node normally
functions as the pacemaker for the entire heart because its intrinsic
Conduction System of the Heart rate is the fastest in the system. From the SA node, signals spread
The conduction system of the heart is a route of specialized out over the atria, causing them to contract.
cardiac muscle fibers that initiate and stimulate contraction of When the signals reach the AV node, there is a slight delay
the atria and ventricles. The conduction system is said to be in- that allows the atria to finish their contraction before the ventri-
trinsic, meaning that the heart beats automatically without the cles begin their contraction. The signal for the ventricles to con-
need for external nervous stimulation. The conduction system tract travels from the AV node through the two branches of the
coordinates the atria and ventricles so they work as a “team,” atrioventricular bundle (AV bundle) before reaching the numer-
that is, the atria contract simultaneously, and the ventricles then ous and smaller Purkinje fibers. The AV bundle, its branches, and
contract simultaneously. Thus, the heart is an effective pump. the Purkinje fibers consist of specialized cardiac muscle fibers that
cardiac
muscle cell
intercalated
1 disk
SA node
AV node 2
AV bundle b.
branches of
atrioventricular
3
bundle Figure 12.5 Conduction system of the heart.
(a) 1 The SA node sends out a stimulus, which causes the atria
4 to contract. 2 When this stimulus reaches the AV node, it passes
Purkinje fibers through the atrial wall to the AV bundle. 3 Action potentials are
conducted down the two branches of the atrioventricular bundle.
4 Numerous small Purkinje fibers carry the electrical signal
throughout the ventricle wall. Thereafter, the ventricles contract.
(b) A cardiac muscle cell showing junctions called intercalated
a. disks (see section 4.3 for review).
efficiently spread an electrical signal throughout the ventricles. electrocardiogram, helps a physician detect and possibly diagnose
Recall from Chapter 4 (p. 73) that cardiac muscle cells are bound the cause of an irregular heartbeat. There are many types of irregular
end-to-end at intercalated disks, and within the disks are adhe- heartbeats, called arrhythmias. The Medical Focus on page 269
sion junctions and gap junctions. Gap junctions are specialized discusses the electrocardiogram and some types of arrhythmias.
intercellular connections that allow electrical current to flow di-
rectly from cell to cell. Once stimulated electrically, the ventricular
muscle contracts purposefully to pump blood. Cardiac Cycle
The SA node pacemaker usually keeps the heartbeat regular. A cardiac cycle includes all the events that occur during one heart-
If the SA node fails to work properly, the ventricles still beat due to beat. On average, the heart beats about 70 times a minute, although
impulses generated by the AV node. But the beat is slower (40 to a normal adult heart rate can vary from 60 to 100 beats per minute.
60 beats per minute). This condition is referred to as a heart block. After tracing the path of blood through the heart, it might seem
An area other than the SA node can become the pacemaker that the right and left sides of the heart beat independently of one
when it develops a rate of contraction that is faster than the SA another, but as you know, they actually contract together. First the
node. This site, called an ectopic pacemaker, may cause an extra two atria contract simultaneously; then the two ventricles contract
beat, if it operates only occasionally, or it can even pace the heart together. The term systole refers to contraction of heart muscle,
for a while. Caffeine and nicotine are two substances that can stim- and the term diastole refers to relaxation of heart muscle. During
ulate an ectopic pacemaker. the cardiac cycle, atrial systole is followed by ventricular systole.
Occasionally, the cardiac conduction system fails to operate As shown in Figure 12.6, the three phases of the cardiac cycle are:
properly. As a result, the heartbeat will be abnormal: failing to beat
Phase 1: Atrial Systole. Time 5 0.15 sec. During this phase, both
at regular intervals, or perhaps beating too slowly or too quickly.
atria are in systole (contracted), while the ventricles are in di-
To correct this, an artificial electronic pacemaker can be surgically
astole (relaxed). Rising blood pressure in the atria forces the
implanted to restore a normal heart rate.
blood to enter the two ventricles through the AV valves. At
this time, both atrioventricular valves are open, and the semi-
Electrocardiogram lunar valves are closed. Atrial systole ends when the atrioven-
With the contraction of any muscle, including the myocardium, elec- tricular valves (tricuspid and bicuspid/mitral) slam shut.
trolyte changes occur that can be detected by electrical recording Closure of the AV valves is caused by the rising pressure of
devices. These changes occur as a muscle action potential sweeps blood filling the ventricle. Remember that closure of the AV
over the cardiac muscle fibers. The resulting record, called an valves causes the first heart sound, “lub” (page 263).
semilunar
valves close
(second heart
pulmonary sound “DUP” heard)
artery semilunar
valves superior
(closed) vena cava
aorta
pulmonary
veins AV valves
left open
right
right atrium atrium
atrium
AV
valves left inferior
open ventricle vena cava c.
a. Phase 3
right Phase 1
pulmonary
ventricle artery
aorta
atrioventricular (AV)
valves close (first heart
sound “LUB” heard)
Phase 2: Ventricular Systole. Time 5 0.30 sec. During this chambers is low. Blood returning to the heart from the supe-
phase, both ventricles are in systole (contracted), while the rior and inferior venae cavae, the coronary sinus, and the
atria are in diastole (relaxed). Rising blood pressure in the pulmonary veins fills the right and left atria and flows pas-
ventricles forces the semilunar valves (aortic and pulmonary) sively into the ventricles. At this time, both atrioventricular
to open. Blood in the right ventricle exits through the valves are open and the semilunar valves are closed.
pulmonary artery trunk to the right and left pulmonary
arteries. Simultaneously, blood in the left ventricle exits into
the aorta. During ventricular systole, both semilunar valves Cardiac Output
are open, and the atrioventricular valves are closed. Ventric- Cardiac output (CO) is the volume of blood pumped out of a ven-
ular systole ends as the ventricles complete their pumping tricle in one minute. (The same amount of blood is pumped out of
job; recall that backflow of blood in the pulmonary artery each ventricle in one minute.) Cardiac output is dependent on two
and aorta forces the semilunar valves to slam shut once more factors:
(page 263). Closure of the semilunar valves causes the sec-
∙ heart rate (HR) 5 beats per minute
ond heart sound “dup.”
∙ stroke volume (SV) 5 amount of blood pumped by a
Phase 3: Atrial and Ventricular Diastole. Time 5 0.40 sec.
ventricle each time it contracts
During this period, both atria and both ventricles are in
diastole (relaxed). At this point, pressure in all the heart Thus, cardiac output 5 HR 3 SV.
The leading cause of heart attack and stroke, and the number-one These components include fibrinogen (the inactive clotting protein
killer in North America and Western Europe, is arteriosclerosis. you learned about in Chapter 11) and a specific lipid called lipopro-
Arteriosclerosis is the older, more generalized term for abnormal tein (a).
thickening and hardening of the arterial wall over time. (However, Once the arterial wall is injured, the body’s defense mechanisms
this term is now seldom used in clinical literature.) The most common respond. White blood cells called macrophages invade the injured
form of arteriosclerosis is atherosclerosis. Scientists agree that ath- area and stick to the arterial wall. These macrophages ingest LDL and
erosclerosis begins with injury to the arterial wall. Research has sug- are then called foam cells (because mixing fat with the cell’s watery
gested several possible causes for injury: smoking, high blood cytoplasm creates a foamy appearance). A collection of foam cells
pressure (called hypertension), low levels of HDL cholesterol (high- creates a fatty streak. Sadly, post-mortem studies on the arteries of
density lipoprotein, often referred to as “good cholesterol”) and young people have shown that these fatty streaks begin to develop
elevated levels of blood lipids, LDL cholesterol (low-density during the early teenage years.
lipoprotein, or “bad cholesterol”), and homocysteine (a by-product of Over time, the artery’s smooth muscle cells migrate to cover
protein metabolism). Diabetics (especially those with type II or non- the fatty streak. Finally, fibroblasts and scar tissue will cover the
insulin-dependent diabetes mellitus) are at increased risk for athero- smooth muscle cells. Calcium ions will invade the tissue, causing it
sclerosis, probably because their disease causes high levels of blood to harden into an atherosclerotic plaque. Atherosclerotic plaques
lipids and LDL cholesterol. can grow so large that they completely block arterial blood flow,
Research also indicates that low-level bacterial or viral infection causing the tissue supplied by the artery to die. Because the plaque’s
that spreads to the blood may injure arterial walls and start the athero- surface is very rough compared to the smooth endothelium, the
sclerosis process. This infection may originate with gum disease, or it plaque may also trigger the clotting mechanism and cause a station-
can be caused by a bacterium called Helicobacter pylori (the microbe ary blood clot, or thrombus, to form inside a blood vessel. Thrombi
that also causes ulcers in the stomach). Antibodies specific to these may also form if the surface of the plaque ulcerates (cracks open and
microbes are found in people with atherosclerosis. In addition, a bleeds). As mentioned in Chapter 11, thromboembolism occurs
blood protein called C-reactive protein, or CRP, is an important piece when a blood clot breaks away from its place of origin and is carried
of evidence suggesting an infection. For example, blood CRP levels to a new location. Further, the plaque can prevent the arterial wall
rise if you suffer from a cold or are recovering from a wound. High cells from receiving oxygen and nutrients. The cells die, causing the
blood levels of CRP in an otherwise healthy person imply that the wall itself to weaken, which might result in an aneurysm. Aneu-
arteries are damaged. Indeed, recent studies show that people with the rysms are weakened areas in the arterial wall, which balloon out-
highest blood levels of CRP have double the risk of heart attack. ward and may even rupture.
Further, new research has shown that excesses of additional blood Coronary artery disease is the term for atherosclerosis of the
components may also be linked to an increased risk of atherosclerosis. coronary arteries (Fig. 12A). If the coronary artery is partially
lumen
of vessel
coronary
artery
ulceration
smooth muscle
muscl
fat
atherosclerotic
fibrous tissue, plaque
calcium, and
a. cholesterol b.
Figure 12A Coronary artery disease. (a) Atherosclerosis begins with injury to an artery; a fatty streak develops at the site
and smooth muscle grows over the lesion. Fibrous tissue and ionic calcium enlarge and stiffen the atherosclerotic plaque.
(b) When plaque is present in a coronary artery, restricted blood flow may result in a heart attack.
—Continued
occluded (blocked) by atherosclerosis, the individual may suffer from of the heart will die from lack of oxygen. Dead tissue is called an
ischemic heart disease. Although enough oxygen normally reaches infarct and, therefore, a heart muscle attack is termed a myocardial
the resting heart, the person’s heart is oxygen-deprived during periods infarction.
of exercise or stress. Some patients experience silent ischemia during Two surgical procedures can reopen occluded coronary arteries.
the earliest stage of the disease; that is, they don’t detect any symp- In balloon angioplasty, a plastic tube is threaded into an artery of an
toms of a problem. However, most patients suffer from angina arm or thigh, then guided through a major blood vessel toward the
pectoris, chest pain that is often accompanied by a radiating pain in heart. Once the tube reaches a blockage, a balloon attached to the end
the left arm. Angina pain is a warning sign of reduced blood flow to of the tube can be inflated to break up a blood clot or open a vessel
the heart and must not be ignored. Should the coronary artery become clogged with plaque (Fig. 12B). Often, a small metal-mesh cylinder
completely blocked by atherosclerotic plaque or thrombus, a portion called a vascular stent is inserted into a blood vessel during balloon
angioplasty. The stent holds the vessels open and decreases the risk
of future occlusion. Stent devices currently in use have built-in medi-
cation, which is slowly released in the artery. These medications
prevent blood clots and additional scar tissue from forming, thus
helping to keep the stent open and blood flowing. In a similar fash-
ion, a stent can be placed into an artery weakened by an aneurysm
(Fig. 12C). This type of stent supports the arterial wall and can be
stent and inflated
balloon monitored externally, allowing a physician to ensure that it is work-
ing properly.
In a coronary bypass operation, a portion of a blood vessel
from another body part (usually one of the mammary arteries from the
chest) is sutured from the aorta to the coronary artery, past the obstruc-
tion point. Blood can then flow normally again from the aorta to the
heart muscle. Figure 12D shows a triple bypass in which three blood
Figure 12B Balloon angioplasty. A balloon inserted in an
vessels connect the aorta to the coronary artery, restoring blood flow
artery can be inflated to open up a clogged coronary blood
vessel. to the myocardium.
grafted vessels
carry arterial
lung
blood
heart
blocked
vessels
stent graft
in aorta
kidney
abdominal
aortic
aneurysm Figure 12D Coronary bypass
surgery. During this operation, the
a. . b. surgeon grafts segments of another
vessel between the aorta and the
Figure 12C Abdominal aortic aneurysm. (a) Before and (b) after stent coronary vessels, bypassing areas of
placement. blockage.
A graph that records the electrical activity of the myocardium during diagnosis, an ECG must be coupled with other information, includ-
a cardiac cycle is called an electrocardiogram, or ECG.*An ECG is ing X rays, studies of blood flow, and a detailed history from the
obtained by placing several electrodes on the patient’s skin, then wir- patient.
ing the electrodes to a voltmeter (an instrument for measuring volt-
age). As the heart’s chambers contract and then relax, the change in *An ECG is sometimes also referred to as an EKG (from the German, ElektroKardioGramm),
polarity is measured in millivolts. because its Dutch inventor spoke German.
T
and more than 100 heartbeats per minute is called tachycardia. P
Another type of arrhythmia is fibrillation, in which the heart beats 0
rapidly but the contractions are uncoordinated. Fibrillation can be Q
very dangerous and potentially deadly, because if the heart muscle is
–.5 S
not contracting properly, the heart will not pump blood. Cells and tis-
sues will subsequently die of oxygen starvation. The heart can some- 0 200 400 600
times be defibrillated by briefly applying a strong electrical current to b. Milliseconds
the chest.
It is important to understand that an ECG only supplies
Figure 12E Electrocardiogram. (a) A portion of an electro-
cardiogram. (b) An enlarged normal cycle.
information about the heart’s electrical activity. To be used in
The CO of an average human is 5,250 ml (or 5.25 L) per cardiac output as much as seven to eight times the normal resting
ventricle, per minute, which equates to about the total volume of amount.
blood in the human body. Each minute, the right ventricle pumps
about 5.25 L through the pulmonary circuit, while the left ven- Heart Rate
tricle pumps about 5.25 L through the systemic circuit. And this A cardioregulatory center in the medulla oblongata of the brain
is only the resting cardiac output! During exercise, cardiac out- can alter the heart rate by way of the autonomic nervous system
put can increase tremendously to meet the body’s need for more (Fig. 12.7). Parasympathetic motor signals conducted by the vagus
oxygen. nerve cause the heart rate to slow, and sympathetic motor signals
Cardiac output can vary because stroke volume and heart rate conducted by sympathetic motor fibers cause the heart rate to
can vary, as discussed next. In this way, the heart regulates the increase.
blood supply, dependent on the body’s needs. For example, in- The cardioregulatory center receives sensory input from re-
creases in heart rate and stroke volume during exercise can increase ceptors within the cardiovascular system. For example, stretch
2
Nerve signals from the baroreceptors
2 signal the cardioregulatory center.
tic)
athe
symp
e rve (para
vagus n
Increased parasympathetic signals
3 decrease heart rate. cardioregulatory
and vasomotor 4
centers in the
Increased sympathetic signals medulla oblongata
4 increase heart rate. sympathetic
nerves
Regulation of blood pressure:
Figure 12.7 Control of heart activity. The cardioregulatory center regulates the heart rate, and the vasomotor center
regulates constriction of blood vessels, according to input received from baroreceptors in the carotid artery and aortic arch.
receptors called baroreceptors are present in the aorta just after it stroke volume. Further, the degree of contraction also depends on
leaves the heart, and also in the carotid arteries, which take blood the correct blood electrolyte concentration. Recall from Chapter 8
from the aorta to the brain. If blood pressure falls, as it sometimes that the proper concentration of ions, or electrolytes, is essential to
does when we stand up quickly, the baroreceptors signal the car- create cardiac muscle action potentials. Without these electrolytes,
dioregulatory center. In response, sympathetic motor signals to the cardiac conduction and contraction are impaired and stroke volume
heart cause the heart rate to increase. Once blood pressure begins to decreases. Two additional factors, venous return and difference in
rise above normal, nerve signals from the cardioregulatory center blood pressure, also influence the strength of contraction.
cause the heart rate to decrease. Such reflexes help control cardiac Venous Return Venous return is the amount of blood entering
output and, therefore, blood pressure, as discussed in section 12.4. the heart by way of the venae cavae (right side of heart) or
The cardioregulatory center is under the influence of the cere- pulmonary veins (left side of heart). The heart adjusts the strength
brum and the hypothalamus. Therefore, when we feel anxious, the of its own contraction beat by beat, based upon venous return. This
sympathetic motor nerves are activated. In addition, the adrenal principle is called the Frank-Starling law. The more blood returned
medulla releases the hormones norepinephrine and epinephrine. to the heart before a given beat, the more the ventricles stretch. As
The result is an increase in heart rate. On the other hand, activities the ventricles are stretched, they contract more and more force-
such as yoga and meditation lead to activation of the vagus nerve, fully. Thus, any event that increases the volume of blood entering
which slows the heart rate. the heart will increase the stroke volume leaving the heart. For
Other factors affect the heart rate as well. For example, a low example, exercise increases the strength of cardiac contraction
body temperature slows the rate. Also, the proper electrolyte con- because skeletal muscle contraction squeezes the veins within
centrations are needed to keep the heart rate regular. muscles and increases venous return. The opposite is also true: If
venous return decreases, stroke volume decreases for the next
Stroke Volume beat. A low venous return, as might happen if there is blood loss,
decreases the strength of cardiac contraction.
Stroke volume, which is the amount of blood that leaves a ventricle,
depends on the strength of heart contraction. As with heart rate, the Difference in Blood Pressure The strength of ventricular con-
autonomic nervous system helps to determine contraction force and traction has to be strong enough to overcome the blood pressure
stroke volume. Sympathetic activity strengthens each contraction and within the attached arteries. If a person has hypertension or athero-
increases stroke volume. By contrast, parasympathetic activity de- sclerosis, the opposing arterial pressure may reduce the effective-
creases both heart rate and contractile force, which in turn decreases ness of contraction and the stroke volume.
a. b. connective
tissue arteriole
a.
precapillary
blood sphincter
c. capillary bed
flow
tunica externa
tunica intima arteriovenous
shunt
v. tunica media
valve venule
blood
flow vein
v = vein; a = artery
Figure 12.8 Blood vessels. (a) The walls of arteries and veins have three layers: tunica intima (interna), tunica media, and tunica
externa. Arteries have a thicker muscle layer and a thick wall, while veins have valves and the larger diameter. (b) A capillary bed lies
between an arteriole and a venule, and flow through it is controlled by a precapillary sphincter. When the sphincter relaxes, blood passes
through the capillary bed and gives up its oxygen to the tissues. Thus, blood goes from being oxygen-rich in the arteriole (red color) to
oxygen-poor in the venule (purple color). When the sphincter contracts, blood can bypass the capillary bed through an arteriovenous
shunt. (c) Photomicrograph of a capillary bed.
between the cells. Large molecules in plasma, such as the plasma does tissue fluid. Therefore, the osmotic pressure of blood pulls
proteins, are too large to pass through capillary walls. Yet, the com- water into and retains water inside a capillary.
position of tissue fluid stays relatively constant because of capil- Notice in Figure 12.9 that a capillary has an arterial end (con-
lary exchange. Tissue fluid is a water-based solution that contains tains arterial blood) and a venous end (contains venous blood). In
sodium chloride, other electrolytes, and scant protein. Any excess between, a capillary has a midsection. We will now consider the ex-
tissue fluid is collected by lymphatic capillaries, which are always change of molecules across capillary walls at each of these locations.
found near blood capillaries.
Three processes influence capillary exchange—blood pres- Arterial End of Capillary
sure, diffusion, and osmotic pressure: When arterial blood enters tissue capillaries, it is bright red be-
cause the hemoglobin in red blood cells is carrying oxygen. Blood
Blood pressure, which is created by the pumping of the heart,
is also rich in nutrients, which are dissolved in plasma.
pushes the blood through the capillary. Blood pressure also
At the arterial end of a capillary, blood pressure, an outward
pushes blood against a vessel’s (e.g., capillary) walls.
force, is higher than osmotic pressure, an inward force. Pressure is
Diffusion, as you know, is simply the movement of substances
measured in terms of mm Hg (mercury). In this case, blood pres-
from the area of higher concentration to the area of lower
sure is 30 mm Hg, and osmotic pressure is 21 mm Hg. Because
concentration.
blood pressure is higher than osmotic pressure at the arterial end
Osmotic pressure is a force caused by a difference in solute con-
of a capillary, water and other small molecules (e.g., glucose and
centration on either side of a membrane.
amino acids) filter out of a capillary at its arterial end.
To understand osmotic pressure, consider that water will dif- Red blood cells and a large proportion of the plasma proteins
fuse across a membrane toward the side that has the greater con- generally remain in a capillary because they are too large to pass
centration of solutes, and the accumulation of this water results in through its wall. The exit of water and other small molecules from a
a pressure. The presence of the plasma proteins, and also salts to capillary creates tissue fluid. Therefore, tissue fluid consists of all the
some degree, means that blood has a greater osmotic pressure than components of plasma, except that it contains fewer plasma proteins.
plasma
salt
protein
Figure 12.9 Capillary exchange. The capillary shows the exchanges that take place and the forces that aid the process. At the
arterial end of a capillary, the blood pressure is higher than the osmotic pressure. Tissue fluid tends to leave the bloodstream. In the midsec-
tion, solutes, including oxygen (O2) and carbon dioxide (CO2), diffuse from high to low concentration. Carbon dioxide and wastes diffuse into
the capillary while nutrients and oxygen enter the tissues. At the venous end of a capillary, the osmotic pressure is higher than the blood
pressure. Tissue fluid tends to re-enter the bloodstream. The red blood cells and the plasma proteins are too large to exit a capillary.
Midsection of Capillary fluid by means of osmotic pressure is not completely effective. The
Diffusion takes place along the length of the capillary, as small body has an auxiliary means of collecting tissue fluid; any excess
molecules follow their concentration gradient by moving from the usually enters lymphatic capillaries.
area of higher to the area of lower concentration. In the tissues,
the area of higher concentration of oxygen and nutrients is always
blood, because after these molecules have passed into tissue fluid,
Veins and Venules
they are constantly being taken up and metabolized by cells. The Veins and smaller vessels called venules return blood from the
cells use oxygen and glucose in the process of cellular respiration, capillary beds to the heart. The venules first drain the blood from
and they use amino acids for protein synthesis. the capillaries and then join together to form a vein. The wall of
As a result of metabolism, tissue cells constantly give off car- a vein is much thinner than that of an artery because the mid-
bon dioxide and other wastes. Because tissue fluid is always the dle layer of muscle and elastic fibers is thinner (see Fig. 12.8).
area of greater concentration for waste materials, they diffuse from Within some veins, especially the major veins of the arms and
tissue fluid into a capillary. legs, valves allow blood to flow only toward the heart when they
are open and prevent the backward flow of blood when they are
Venous End of Capillary closed.
At any given time, more than half of the total blood volume is
At the venous end of the capillary, blood pressure is much reduced
found in the veins and venules. If blood is lost due to, for example,
to only about 15 mm Hg, as shown in Figure 12.9. Blood pressure is
hemorrhaging, sympathetic nervous stimulation causes the veins to
reduced at the venous end because capillaries have a greater cross-
constrict, providing more blood to the rest of the body. In this way,
sectional area at their venous end than their arterial end. However,
the veins act as a blood reservoir.
there is no reduction in osmotic pressure, which remains at 21 mm
Hg and is now higher than blood pressure. Therefore, water tends
to diffuse into a capillary at the venous end. As water enters a capil- Varicose Veins and Phlebitis
lary, it brings with it additional waste molecules. Blood that leaves Varicose veins are abnormal and irregular dilations in superficial
the capillaries to drain into veins is deep maroon in color because (near the surface) veins, particularly those in the lower legs. Vari-
red blood cells now contain reduced hemoglobin—hemoglobin cose veins in the rectum, however, are commonly called piles, or
that has given up its oxygen and taken on hydrogen ions. more properly, hemorrhoids. Varicose veins develop when the
In the end, about 85% of the water that left a capillary at the valves of the veins become weak and ineffective due to backward
arterial end returns to it at the venous end. Therefore, retrieving pressure of the blood.
Magnitude
a. tunica externa—tunica intima—tunica media
b. tunica media—tunica externa—tunica intima
c. tunica externa—tunica media—tunica intima
8. If you described the differences between arteries and veins,
small arteries
large arteries
you could say:
small veins
large veins
vena cava
capillaries
arterioles
venules
a. Arteries have a thicker wall than veins.
aorta
b. Veins have valves but arteries do not.
c. Veins return blood to the heart; arteries carry blood away
from the heart. Blood Flow
d. All of these statements are correct. Figure 12.10 Velocity of blood flow changes throughout the
9. Blood pressure is greatest at: systemic circuit. Velocity changes according to the total cross-
a. the venous end of a capillary bed. sectional area of vessels.
b. the arterial end of a capillary bed.
c. the center of a capillary bed.
d. no single area; it is equal throughout the capillary bed. Once blood has left the capillaries, blood velocity increases
as venules combine to form larger and larger veins. Thus, velocity
Answers in Appendix A.
in the venous system is greatest in the venae cavae, which are the
largest veins. However, the velocity of venous blood flow returning
to the heart is always lower than that of arterial blood leaving the
12.4 Physiology of Circulation heart. Contractions of the powerful left ventricle generate a greater
11. Explain how blood pressure changes throughout the vascular velocity for arterial blood. The velocity of the arterial and venous
system, and describe the factors that determine blood pressure. systems working together is very high—in a resting individual, it
12. Describe how blood pressure is regulated.
13. Define pulse, and tell where the pulse may be taken. takes only about a minute for a drop of blood to go from the heart
14. Describe shock due to hypotension and various medical conse- to the foot and back again to the heart!
quences of hypertension.
Blood Pressure
Circulation is the movement of blood through blood vessels, from
Blood pressure is the force of blood against the walls of blood
the heart to the body and then back to the heart. In this section, we
vessels. You would expect arterial blood pressure to be highest
discuss various factors affecting circulation.
in the aorta. Why? Because the pumping action of the powerful,
thick-muscled left ventricle forces blood into the aorta. Further,
Velocity of Blood Flow Figure 12.11 shows that systemic blood pressure decreases progres-
The velocity of blood flow is slowest in the capillaries. What might sively with distance from the left ventricle. Blood pressure is lowest
account for this? Consider that the aorta branches into the other in the venae cavae because they are farthest from the left ventricle.
arteries, and these in turn branch into the arterioles, and so forth Note also in Figure 12.11 that blood pressure fluctuates in the
until blood finally flows into the capillaries. As you know, the arterial system between systolic blood pressure and diastolic blood
diameter of these vessels decreases, getting smaller and smaller pressure. Certainly, we can correlate this with the action of the
with each branching. Capillary diameter is so small that blood heart. During systole, the left ventricle is pumping blood out of the
cells must travel through in single file. In addition, each time an heart, and during diastole the left ventricle is resting.
artery branches, the total cross-sectional area of the blood vessels More important than the systolic and diastolic pressure is the
increases, reaching the maximum cross-sectional area in the capil- mean arterial blood pressure (MABP), the pressure in the arterial
laries (Fig. 12.10). The slow rate of blood flow in the capillaries system averaged over time. It is important to note that MABP is
is beneficial because it allows time for the exchange of gases in not determined by taking the average of systolic and diastolic pres-
pulmonary capillaries and for the exchange of gases and nutrients sures. Rather, MABP is the product of cardiac output (CO) times
for wastes in systemic capillaries (see Fig. 12.9). peripheral resistance. (Recall that cardiac output equals heart rate
re
ss
100
Systemic Blood Pressure (mm Hg)
ure
80
dias
toli
cp
re
ss
60
ur
e
40
small arteries
large arteries
small veins
large veins
vena cava
capillaries
arterioles
20
venules
aorta
Blood Pressure
Blood pressure is usually measured in the brachial artery with a
sphygmomanometer, an instrument that records changes in terms
radial artery of millimeters (mm) of mercury (Fig. 12.15). A blood pressure
cuff connected to the sphygmomanometer is wrapped around the
patient’s arm, and a stethoscope is placed over the brachial artery.
The blood pressure cuff is inflated until no blood flows through
femoral artery
it; therefore, no sounds can be heard through the stethoscope. The
cuff pressure is then gradually lowered. As soon as the cuff pres-
sure declines below systolic pressure, blood flows through the bra-
chial artery each time the left ventricle contracts. The blood flow is
popliteal artery turbulent below the cuff. This turbulence produces vibrations in the
(behind knee) blood and surrounding tissues that can be heard through the stetho-
scope. These sounds are called Korotkoff sounds, and the cuff
pressure at which the Korotkoff sounds are heard the first time is
the systolic pressure. As the pressure in the cuff is lowered still
posterior more, the Korotkoff sounds change tone and loudness. When the
dorsalis
pedis artery tibial artery cuff pressure no longer constricts the brachial artery, no sound is
heard. The cuff pressure at which the Korotkoff sounds disappear
is the diastolic pressure.
Normal resting blood pressure for a young adult is 120/80. The
Figure 12.14 Pulse points. Pulse points are the locations higher number is the systolic pressure, the pressure recorded in an
where the pulse can be taken. Each pulse point is named after
the appropriate artery.
artery when the left ventricle contracts. The lower number is the
300
280
260
240
220 No sounds
200 (artery is closed)
180 Figure 12.15 Use of
160 a sphygmomanometer.
140
systole The technician inflates
120 Sounds heard
100
(artery is opening the cuff with air, gradu-
80 diastole
60
and closing) ally reduces the pres-
40 sure, and listens with a
No sounds
20
(artery is open) stethoscope for the
0
sounds that indicate
blood is moving past
inflatable rubber cuff the cuff in an artery.
This is systolic blood
air hose from squeezable bulb pressure. The pressure
(inflates cuff with air)
in the cuff is further re-
duced until no sound is
sounds are heard with stethoscope
heard, indicating that
blood is flowing freely
through the artery. This
is diastolic pressure.
How many people’s lives have been saved during cardiac arrest by car- for every 30 chest compressions. Continue CPR until you’re re-
diopulmonary resuscitation (CPR)? The exact number would probably lieved by emergency responders.
be impossible to track, according to the American Heart Association • If you have access to an automated external defibrillator (AED),
(AHA). Regrettably, it’s easier to track the tragedies that occur without use it. This computerized device is available in many public
it: Fewer than 30% of people who suffer cardiac arrest ever receive by- places, such as airports and shopping malls, and is prominently
stander help. Onlookers simply don’t know what to do, or perhaps are labeled. An AED will explain, step by step, how to check for the
afraid that they might do something wrong. For this reason, the AHA person’s breathing and a pulse first. Next, it will describe how to
has published the Chain of Survival, a new set of four guidelines that apply pads to the victim’s chest so that the computer can analyze
make it easier to help a person in cardiac arrest: the heart activity. If a shock is needed to restart the victim’s heart,
external carotid a.
internal carotid a. vertebral a.
right common carotid a. left common carotid a.
right subclavian a. left subclavian a.
brachiocephalic a.
aortic arch
axillary a. ascending aorta aorta
descending aorta
intercostal a.
thoracic aorta
deep brachial a.
brachial a. celiac a.
abdominal aorta
renal a. superior mesenteric a.
radial a.
inferior mesenteric a.
common iliac a.
internal iliac a. gonadal a.
external iliac a.
ulnar a.
deep femoral a.
femoral a.
popliteal a.
anterior tibial a.
posterior tibial a.
fibular a.
dorsalis pedis a.
Each external jugular vein enters a subclavian vein. In turn, the and then enters the liver. Emerging from the liver, the hepatic
subclavian veins join with the internal jugular veins to form the veins enter the inferior vena cava.
brachiocephalic veins. Right and left brachiocephalic veins merge, In the pelvic region, veins from the various organs enter
giving rise to the superior vena cava. the internal iliac veins, while the veins from the lower limbs
In the abdominal cavity, paired veins return blood from bilat- enter the external iliac veins. The internal and external iliac
eral structures such as the kidneys and gonads. In addition, as dis- veins become the common iliac veins that merge, forming the
cussed in more detail later, the hepatic portal vein receives blood inferior vena cava. Table 12.2 lists the principal veins that enter
from the stomach, spleen, intestines, and other abdominal organs, the venae cavae.
internal jugular. v
subclavian v.
right brachiocephalic v. left brachiocephalic v.
axillary v. superior vena cava
cephalic v.
brachial v. hepatic v.
basilic v. inferior vena cava
median cubital v.
radial v.
renal v. ascending lumbar v.
ulnar v.
gonadal v.
common iliac v.
internal iliac v.
external iliac v.
femoral v.
great saphenous v.
popliteal v.
posterior tibial v.
small saphenous v.
anterior tibial v.
liver
stomach
gastric veins
spleen
splenic vein
inferior mesenteric
vein
small intestine
Figure 12.18 Hepatic portal system. This system provides venous drainage of the digestive organs and takes venous
blood to the liver.
anterior communicating
artery
anterior cerebral artery
basilar artery
vertebral artery
off branches that join to form the cerebral arterial circle (circle The path of blood in the fetus can be traced, beginning from
of Willis), a vascular route in the region of the pituitary gland the right atrium (Fig. 12.20). Most of the blood that enters the
(Fig. 12.19). Because the blood vessels form a circle, alternate right atrium passes directly into the left atrium by way of the
routes are available for bringing arterial blood to the brain and thus foramen ovale because the blood pressure in the right atrium
supplying the brain with oxygen. The presence of the cerebral arte- is somewhat greater than that in the left atrium. The rest of the
rial circle also equalizes blood pressure in the brain’s blood supply. fetal blood entering the right atrium passes into the right ven-
tricle and out through the pulmonary trunk. However, because
Fetal Circulation of the ductus arteriosus, most pulmonary trunk blood passes
As Figure 12.20 shows, the fetus has four circulatory features that directly into the aortic arch. Notice that whatever route blood
are not present in adult circulation: takes, most of it reaches the aortic arch instead of the pulmonary
circuit vessels.
1. The foramen ovale, or oval window, is an opening between Blood within the aorta travels to the various branches, includ-
the two atria. This window is covered by a flap of tissue that ing the iliac arteries, which connect to the umbilical arteries lead-
acts as a valve. ing to the placenta. Diffusion of oxygen, nutrients, carbon dioxide,
2. The ductus arteriosus, or arterial duct, is a connection and metabolic wastes between maternal and fetal blood takes place
between the pulmonary artery and the aorta. It is found on at the placenta. There, oxygen and nutrients diffuse from mother to
the superior pulmonary trunk near the origin of the left fetus, while carbon dioxide and waste simultaneously travel from
pulmonary artery. fetus to mother. It’s important to note that maternal and fetal blood
3. The umbilical arteries and vein are vessels that travel to and do not mix at the placenta during a normal pregnancy. Oxygenated
from the placenta, leaving waste and receiving nutrients. blood from the placenta then returns to the fetus’s body through
4. The ductus venosus, or venous duct, is a connection the umbilical vein.
between the umbilical vein and the inferior vena cava. Thus, blood in the umbilical arteries is O2-poor, but blood in
All of these features can be related to the fact that the fetus the umbilical vein, which travels from the placenta, is O2-rich. The
does not use its lungs for gas exchange—it receives oxygen and umbilical vein enters the ductus venosus, which passes directly
nutrients from the mother’s blood at the placenta. During develop- through the liver. The ductus venosus then joins with the inferior
ment, the lungs receive only enough blood to supply their develop- vena cava, a vessel that contains O2-poor blood. The vena cava
mental need for oxygen and nutrients. returns this mixture to the right atrium.
pulmonary artery
aortic arch
pulmonary trunk
foramen ovale
(becomes fossa ovalis) left atrium
abdominal aorta
ductus venosus
(becomes ligamentum
venosum)
umbilical vein
Decreasing
blood
placenta oxygen
umbilical arteries level
Figure 12.20 Fetal circulation. Arrows indicate the direction of blood flow. The lungs are not functional in the fetus, but
they are developing. The blood passes directly from the right atrium to the left atrium via the foramen ovale or from the right
ventricle to the aorta via the pulmonary trunk and ductus arteriosus. The umbilical arteries take fetal blood to the placenta
where exchange of molecules between fetal and maternal blood takes place. Oxygen and nutrient molecules diffuse into the
fetal blood, and carbon dioxide and urea diffuse from the fetal blood. The umbilical vein returns blood from the placenta to
the fetus.
Changes at Birth Sectioning and tying the umbilical cord per- number of cases, the passage of O2-poor blood from the right side
manently separates the newborn from the placenta. The newborn’s to the left side of the heart is sufficient to cause cyanosis, a bluish
first breath inflates the lungs, and oxygen enters the blood at the cast to the skin. This condition can now be corrected by open-heart
lungs instead of the placenta. O2-rich blood returning from the surgery.
lungs to the left side of the heart usually causes a flap on the left The fetal blood vessels and shunts constrict and become
side of the interatrial septum to close the foramen ovale. What re- fibrous connective tissue called ligamentums in all cases except the
mains is a depression called the fossa ovalis. Incomplete closure distal portions of the umbilical arteries, which become the medial
occurs in nearly one out of four individuals, but even so, blood umbilical ligaments. Regardless, these structures run between in-
rarely passes from the right atrium to the left atrium because either ternal organs. For example, the ligamentum teres (which is the
the opening is small or it closes when the atria contract. In a small remnant of the umbilical vein) attaches the umbilicus to the liver.
All of us can take steps to prevent cardiovascular disease, the most The Do’s
frequent cause of death in the United States. Genetic factors that pre- Healthy Diet
dispose an individual to cardiovascular disease include family history Of all the possible dietary changes one could make to prevent cardio-
of heart attack under age 55, male gender, and ethnicity (African vascular disease, the most important will be to switch to a diet low in
Americans are at greater risk). However, people with one or more of saturated fats, trans fats, and cholesterol. These three are found most
these risk factors don’t have to give up. It only means that they need often as the “solid” forms of fat: butter, margarine, shortening, lard, and
to pay particular attention to the following guidelines for a heart- the marbling found on fatty meat. Trans fats can be found in baked
healthy lifestyle. goods as well. Instead, replace these fats with monounsaturated fats
(found in nuts, olives, and olive oil) polyunsaturated fats (found in veg-
The Don’ts etable oils) and omega-3 fatty acids (found in fish, especially fatty fish
Smoking such as salmon, mackerel, and trout). Healthy fats like these can help to
Hypertension is recognized as a major contributor to cardiovascular lower total cholesterol and low-density lipoprotein (LDL), while boost-
disease. When a person smokes, the drug nicotine, present in cigarette ing high-density lipoprotein (HDL). Those changes are very important:
smoke, enters the bloodstream. Nicotine causes the arterioles to con- In our bodies, cholesterol is ferried in the blood by LDL and HDL. LDL
strict and the blood pressure to rise. Restricted blood flow and cold (often referred to as “bad cholesterol” by physicians) takes cholesterol
hands are associated with smoking in most people. Cigarette smoke from the liver to the tissues. Recall (from the Medical Focus on
also contains carbon monoxide, and hemoglobin combines preferen- pages 267–268) that in blood vessels, LDL is oxidized by macrophages
tially and nonreversibly with carbon monoxide. Therefore, the pres- to form foam cells, and later, a fatty streak that begins an atherosclerotic
ence of carbon monoxide lowers the oxygen-carrying capacity of the plaque. HDL (“good” cholesterol) transports cholesterol out of the tis-
blood, and the heart must pump harder to propel the blood through the sues to the liver, where cholesterol is metabolized. When the LDL level
lungs. Smoking also damages the arterial wall and accelerates the in the blood is abnormally high or the HDL level is abnormally low,
formation of atherosclerosis and plaque. cholesterol accumulates in artery walls. Substituting heart-healthy fats
in the diet has been shown to decrease the risk of cardiovascular dis-
Drug Abuse
ease—but it’s important to recognize that all fats are very calorie-dense,
Stimulants, such as cocaine and amphetamines, can cause an irregular
and must be used in moderation to avoid weight gain.
heartbeat and lead to heart attacks even in people who are using drugs
Limiting sodium intake is another important step to take in mod-
for the first time. Intravenous drug use may also result in a cerebral
ifying diet. In 2009, data from the Centers for Disease Control showed
blood clot and stroke.
that approximately 70% of Americans are salt-sensitive, and their
Too much alcohol can destroy just about every organ in the body,
blood pressure tends to rise after consumption of excess sodium. In
the heart included. But investigators have discovered that people who
response, the American Heart Association lowered its recommended
take an occasional drink have a 20% lower risk of heart disease than
daily sodium intake to less than 1500 milligrams (mg). Almost all
do those who completely abstain from alcohol. Two to four drinks a
processed food contains sodium, so watch those nutrition labels!
week is the recommended limit for men; one to three drinks is the
Here’s another recommendation from the American Heart Asso-
recommendation for women.
ciation, and it may surprise you how few Americans actually do it. Only
Research has shown that wines (and especially red wine) contain
about 27% of us eat those five servings of fruits and vegetables daily.
antioxidants which can further help to reduce the risk of cardiovascu-
Evidence is mounting to suggest a role for antioxidant vitamins (A, E,
lar damage.
and C) in the prevention of cardiovascular disease, and the best sources
Weight Gain are in plant-based food. Antioxidants protect the body from free radi-
Hypertension also occurs more often in persons who are more than cals that may damage HDL cholesterol through oxidation or damage the
20% above the recommended weight for their height. Because more lining of an artery, leading to a blood clot that can block the vessel. It’s
tissue requires servicing, the heart must send extra blood out under not all about vitamins either: By creating a feeling of fullness, all that
greater pressure in those who are overweight. It may be very difficult fiber found in fruits and vegetables can help with weight loss.
to lose weight once it is gained, and therefore weight control should
be a lifelong endeavor. Even a slight decrease in weight can bring a Regular Health Screenings
reduction in hypertension. A 4.5-kilogram weight loss doubles the It is recommended that everyone know his or her blood cholesterol level,
chance that blood pressure can be normalized without drugs. as well as levels of HDL, LDL, and triglyceride. Individuals with a high
—Continued
total blood cholesterol level (240 mg/100 ml) should be further tested to illness, but enough to injure the endothelial lining and start the formation
determine their LDL cholesterol level. Blood tests can also determine of atherosclerotic plaques. Proper care of the teeth and gums, along with
high levels of homocysteine and C-reactive protein, two important indi- regular visits to the dentist, just might prevent cardiovascular disease.
cators that atherosclerosis is occurring. Levels of these two markers,
along with LDL cholesterol level, must be considered together with Exercise
other cardiovascular risk factors such as age, family history, general People who exercise are less apt to have cardiovascular disease. Exer-
health, and whether the patient smokes. Further, for those with a strong cise helps keep weight under control, may help minimize stress, and
family history of cardiovascular disease, testing may be recommended reduces hypertension. The heart beats faster when exercising, but
for elevated levels of fibrinogen and lipoprotein (a), two blood compo- exercise slowly increases the heart’s capacity. This means that the
nents that may indicate atherosclerosis. A person with a moderate risk of heart can beat more slowly when we’re at rest and still do the same
cardiovascular disease may have success with dietary therapy to lower amount of work. The American Heart Association recommends at
LDL. Cholesterol-lowering drugs are reserved for high-risk patients. least 150 minutes per week of moderate exercise: 30 minutes a day,
for 5 days per week. Those 30 minutes can even be broken into three
Proper Dental Care 10-minute sessions, making regular daily exercise an attainable goal
Periodontal disease, the inflammation of the gums caused by poor dental for practically everyone. In addition, practice meditation and yoga-
hygiene, has been suggested as a cause for atherosclerosis. Scientists like stretching and breathing exercises to reduce stress.
suspect that people with tooth decay and gum disease may have a low- For more information about cardiovascular disease prevention,
level bacterial infection in the blood—not severe enough to cause visit the American Heart Association website: http://www.heart.org
Summary
12.1 Anatomy of the Heart C. The first heart sound, “lub,” is 12.3 Anatomy of Blood Vessels
The heart keeps oxygen-poor caused by AV valve closure. The Blood vessels transport blood, carry
blood separate from oxygen-rich second heart sound, “dup,” out exchange in pulmonary and sys-
blood and keeps blood flowing in occurs when the semilunar valves temic capillaries, regulate blood
one direction. It creates blood close. When valves don’t work pressure, and direct blood flow.
pressure and regulates the supply properly, they can be replaced A. Arteries and arterioles carry
of blood to meet current needs. with synthetic or pig valves. blood away from the heart.
The right side of the heart pumps D. The myocardium is supplied with B. Capillaries are made of endothe-
blood to the lungs via the pulmo- blood from the coronary circula- lial cells and have precapillary
nary circuit; the left side pumps tion. Coronary artery disease is sphincters.
blood to the tissues via the sys- caused by atherosclerosis. C. Capillary exchange occurs via a
temic circuit. 12.2 Physiology of the Heart balance of hydrostatic and osmotic
A. The heart is covered by the peri- A. The conduction system of the pressures. At the arterial end of a
cardium. The visceral pericar- heart includes the SA node, the capillary, outward hydrostatic pres-
dium also functions as the AV node, the AV bundle, the bun- sure is greater and tissue fluid
epicardium of the heart wall. The dle branches, and the Purkinje accumulates. At the venous end,
myocardium is made of cardiac fibers. The SA node causes the osmotic pressure is greater and
muscle, and the endocardium is atria to contract. The AV node and tissue fluid is reabsorbed.
the heart’s inner lining. the rest of the conduction system 12.4 Physiology of Circulation
B. The heart has right and left sides cause the ventricles to contract. A. Velocity of blood flow varies
and four chambers: two atria and B. The heartbeat (cardiac cycle) is according to total cross-sectional
two ventricles. There are two divided into three phases: (1) In area; therefore, blood flow is
atrioventricular valves separating atrial systole, the atria contract; slowest in the capillaries.
the atria from the ventricles: the (2) in ventricular systole, the ven- B. Blood pressure decreases with
right tricuspid valve and the left tricles contract; and (3) in atrial distance from the left ventricle.
bicuspid, or mitral, valve. On the and ventricular diastole, both the Cardiac output (CO) and
right side, the pulmonary semilu- atria and the ventricles rest. resistance to flow determine
nar valve controls blood flow C. The cardiac output (amount of blood pressure. Venous return af-
from the right ventricle into the blood discharged by the heart in fects CO. The skeletal muscle
pulmonary artery. On the left one minute) is the product of pump and the respiratory pump
side, the aortic semilunar valve stroke volume and heart rate. The assist venous return. A vasomotor
controls blood flow from the left heart rate is regulated largely by center regulates peripheral resis-
ventricle into the aorta. the cardioregulatory center and tance. Neural regulation of periph-
the autonomic nervous system. eral resistance is via a vasomotor
Study Questions
1. State the location and functions of the 8. What types of blood vessels are in the 13. Trace the path of blood from the aorta
heart. (p. 260) body? Discuss their structure and func- to the femoral artery to the dorsalis
2. Describe the wall and coverings of the tion. (pp. 271–274) pedis artery in the foot. Then, trace a
heart. (p. 261) 9. What factors determine velocity of return pathway from the foot through
3. Name the chambers and valves of the blood flow? Blood pressure? In what the great saphenous vein and back to
heart. Trace the path of blood through vessel is blood pressure highest? Low- the aorta. Indicate which of the ves-
the heart. (pp. 261–263) est? (pp. 274–275) sels are in the systemic circuit and
4. Describe the coronary circuit, and dis- 10. What mechanisms assist venous re- which are in the pulmonary circuit.
cuss several coronary circuit disorders. turn to the heart? Discuss nervous and (pp. 279–281)
(pp. 263, 267–268) hormonal control of blood pressure. 14. Compare the fetal circulation with that
5. Describe the conduction system of the (pp. 275–276) of an adult. How are they alike? How
heart and how conduction can be 11. What is pulse? How do you take a per- are they different? (pp. 283–284)
recorded using an electrocardiogram. son’s pulse? How do you take a per- 15. Give examples to show that the cardio-
(pp. 264–265, 269) son’s blood pressure? What does a vascular system functions to maintain
6. Describe the cardiac cycle (using the blood pressure of 120/80 mean? homeostasis and that interactions with
terms systole and diastole), and explain (pp. 276–278) other systems help it and the other
the heart sounds. (pp. 265–266) 12. What are hypertension, stroke, systems to maintain homeostasis.
7. What is cardiac output (CO)? What two aneurysm, and congestive heart fail- (pp. 287–289)
factors determine CO? How are these ure? (pp. 267–268, 278, 286–287)
factors regulated? (pp. 266, 269–271)
Learning Outcomes After you have studied this chapter, you should be able to:
13.1 Lymphatic System 6. Describe the body’s specific defense Medical Focus
mechanisms: antibody-mediated
1. Describe the functions of the The Lymphatic System and Illness
immunity and cell-mediated
lymphatic system. immunity.
2. Explain the structure of lymphatic 7. Give examples of immunotherapeutic
Visual Focus
vessels and the path of lymph from drugs. Steps of the Inflammatory Reaction
the tissues to the cardiovascular
veins.
13.4 Creating an Immune Response Medical Focus
13.2 Organs, Tissues, and Cells of 8. Explain natural active and passive AIDS Epidemic
immunity, and describe how Immunization: The Great Protector
the Immune System artificial active and passive immunity Influenza: A Constant Threat of Pandemic
3. Describe the structure and function are created.
of the primary lymphatic organs: red 9. Give examples of disorders caused
bone marrow and the thymus gland. What’s New
by excessive and inadequate
4. Describe the structures and immune system responses. Parasite Prescription for Autoimmune
functions of the secondary lymphatic Disease
organs: the spleen and the lymph 13.5 Effects of Aging
nodes. Human Systems Work Together
10. Describe the anatomical and
physiological changes that occur in Lymphatic System
13.3 Nonspecific and Specific the immune system as we age.
Defenses
5. Outline the body’s nonspecific 13.6 Homeostasis
defense mechanisms: barriers to 11. Describe how the lymphatic system
entry, inflammatory reaction, natural works with other systems of the
killer cells, and protective proteins. body to maintain homeostasis.
293
axillary lymph nodes: thymus: lymphatic tissue where T lymphocytes mature and
located in the underarm region learn to tell "self" from "nonself"
tissue
fluid
lymphatic
capillary
tissue cell
inguinal lymph nodes:
located in the groin region; blood
cleanse lymph and alert capillary
the immune system to
pathogens b.
c.
lobule
cortex capsule
Figure 13.1 The lymphatic system. (a) Lymphatic vessels drain excess fluid from the tissues and return it to the
cardiovascular system. (b) The enlargement shows a lymphatic vessel. (c) The red bone marrow, thymus gland, lymph nodes, and spleen
are among those lymphatic organs that assist immunity.
As the “next-door neighbor” to the cardiovascular system, the parallel tissue cells. Thus, edema can lead to tissue damage and eventual
lymphatic system defends against infectious disease and cancer, and death, illustrating the importance of tissue fluid collection by the
regulates fluid balance in the tissues. Failure of the lymphatic system lymphatic system.
to maintain homeostatic balance in these critical areas results Blockage of the lymphatic vessels prevents proper tissue fluid
in disease. drainage, resulting in edema. As mentioned previously, surgical
The internal structure of a lymph node is designed to filter out removal of lymph nodes is a common treatment for cancer. How-
from lymph and then destroy any foreign material, including microbes ever, node removal often blocks lymphatic drainage, producing a
and cancer cells. An infection that causes swelling and tenderness of painful and debilitating lymphedema for the patient. A dramatic
nearby lymph nodes is called lymphadenitis. If the infection is not example of edema caused by lymphatic obstruction occurs when a
contained, lymphangitis, an infection of the lymphatic vessels, may parasitic roundworm clogs the lymphatic vessels. Tremendous
result. Red streaks can be seen through the skin, indicating that the swelling of the arm, leg, or external genitals results, causing a con-
infection may have spread to the bloodstream. dition called elephantiasis.
Like microbes, cancer cells sometimes enter lymphatic vessels Edema can also be due to a low osmotic pressure of the blood,
and move undetected to other regions of the body, where they produce as when plasma proteins are excreted by the kidneys instead of
secondary tumors. In this way, the lymphatic system sometimes being retained in the blood. Extra tissue fluid forms, and lymphatic
assists metastasis, the spread of cancer far from its place of origin. vessels may not be able to absorb it all. Pulmonary edema is a life-
Because of this potential for metastasis, regional lymph nodes are threatening condition associated with congestive heart failure.
usually removed for examination whenever surgery is used to diag- When the heart muscle is damaged and unable to effectively empty
nose or treat cancer. The presence or absence of tumor cells in the the heart, blood backs up in the pulmonary circulation. Pulmonary
nodes can be used to determine how far the cancer has spread. Lymph capillary blood pressure increases, which leads to excess fluid in
node biopsy (the microscopic study of the tissue) also aids in making lung tissue. Congested lung tissue cannot properly exchange
decisions concerning additional treatment, such as radiation or oxygen and carbon dioxide with the blood, and the patient may
chemotherapy. suffocate.
Failure of the lymphatic vessels to properly remove tissue Cancer of lymphatic tissue is called lymphoma. In Hodgkin
fluid results in a condition called edema. Edema forms because too disease, billions of lymphoma cells create swollen lymph nodes
much tissue fluid is made and/or not enough tissue fluid is drained throughout the body. The lymphoma cells can migrate and grow in the
away. Excessive tissue fluid can compress the blood vessels within spleen, liver, and bone marrow. The prognosis is good, however, if
a tissue, preventing the flow of blood, oxygen, and nutrients to Hodgkin disease is diagnosed early.
Lymph Nodes
Begin Thinking Clinically
Lymph nodes, which are small, ovoid structures, occur along
Why do surgeons remove lymph nodes at the same time
lymphatic vessels. Connective tissue forms the capsule of a lymph
that a cancer is taken out? What is a sentinel node?
node and also divides the organ into compartments (see Fig. 13.1).
Each compartment contains a nodule packed with B lymphocytes Answer and discussion in Appendix A.
and a sinus that increases in size toward the center of the node. As
lymph courses through the sinuses, it is filtered by macrophages
(phagocytic white blood cells), which engulf pathogens and de- Lymphatic Nodules
bris. T lymphocytes, also present in sinuses, fight infections and Lymphatic nodules are concentrations of lymphatic tissue not sur-
attack cancer cells. rounded by a capsule. The tonsils are lymphatic nodules located
Each portion of the anterior body cavity (see Fig. 1.5) contains in the posterior pharynx (see Fig. 14.2). A single pharyngeal
superficial and deep lymph nodes, named for their location. For tonsil (also referred to as adenoids) is in the nasopharynx, whereas
example, inguinal nodes are in the groin, and axillary nodes are in lingual tonsils sit at the base of the tongue. Palatine tonsils are
the armpits. Physicians often examine for the presence of swollen, visible in the posterior oral cavity. Like lymph nodes, the tonsils
tender lymph nodes as evidence that the body is fighting an infec- contain both T and B lymphocytes. Because of their location, they
tion. This is a noninvasive, preliminary way to help make such a are the first to encounter pathogens and antigens that enter the body
diagnosis. by way of the nose and mouth.
4. List and describe two functions of the thymus gland. Inflammatory Reaction
5. Which lymphatic organ functions as a blood reservoir and In a situation where the first line of defense is inadequate, the
removes dead and dying red blood cells?
body’s second line of defenses will activate. These mechanisms
a. thymus c. appendix involve the inflammatory response, accompanied by the actions of
b. Peyer patches d. spleen phagocytic cells, natural killer cells, and protective proteins. Like
6. Which of the following structures has a connective tissue the first line of defense, this second set of responses is nonspecific.
capsule? Whenever tissue is damaged by physical or chemical agents
a. axillary lymph nodes c. Peyer patches or by pathogens, a series of events occurs that is known as the
b. palatine tonsils d. adenoids (pharyngeal tonsil) inflammatory reaction. The inflammatory reaction has four out-
ward signs: redness, swelling, heat, and pain. All of these signs
Answers in Appendix A.
are due to capillary changes in the damaged area. Figure 13.3
illustrates the five basic steps of an inflammatory response:
13.3 Nonspecific and Specific Defenses 1. Chemical mediators, such as histamine, cause capillaries to
5. Outline the body’s nonspecific defense mechanisms: barriers to dilate and become more permeable. These tissue chemicals are
entry, inflammatory reaction, nonspecific phagocytic white blood released by damaged tissue cells and by mast cells found in
cells, natural killer cells, and protective proteins.
the tissues. Mast cells resemble basophils, one of the types of
6. Describe the body’s specific defense mechanisms: antibody-
mediated immunity and cell-mediated immunity. white blood cells (see section 11.2 to review the types of white
7. Give examples of immunotherapeutic drugs. blood cells). Excess blood flow to the inflamed area causes the
skin to redden and become warm. Elevated temperature tends
Immunity includes nonspecific defenses and specific defenses. The to inhibit the growth of some pathogens, and heightened blood
five types of nonspecific defenses—barriers to entry, the inflam- flow brings more defensive white blood cells to the area.
matory reaction, nonspecific phagocytic white blood cells, natural 2. Increased capillary permeability allows fluids and proteins,
killer cells, and protective proteins—are effective against many including blood clotting factors, to escape into the tissues.
types of infectious agents. Specific defenses are effective against a Escaped fluid causes swelling in the affected areas, putting
particular infectious agent. pressure on nearby pain neurons and causing pain. Further,
the inflammatory chemicals themselves can also stimulate
Nonspecific Defenses the pain sensation. Although we can all agree that pain is a
big nuisance, it’s also a warning that tissue has been injured,
Barriers to Entry and we need to try to correct the situation.
The body has built-in barriers, both physical and chemical, that 3. Edema and clots that form in the injured area help to “wall
help to prevent infection by microbes. These barriers are the first off” the area from the rest of the body. Thus, if pathogens
line of defense against infection. The intact skin is generally a very have entered the body during injury, they will not be able to
effective physical roadblock that prevents infection. Mucous mem- cause a systemic infection.
branes lining the respiratory, digestive, reproductive, and urinary 4. Migration of phagocytes, primarily neutrophils and mono-
tracts are also physical barriers to entry by pathogens. (However, cytes, also occurs during the inflammatory reaction. Neutro-
it must be noted that their effectiveness is limited, especially in phils and monocytes are amoeboid (see Figure 11.6) and can
the oral and nasal cavities, because most cold viruses enter the change shape to squeeze through capillary walls and enter
body by crossing these membranes.) The ciliated cells that line the tissue fluid. There, they phagocytize pathogens.
upper respiratory tract sweep mucus and trapped particles up into 5. After monocytes appear on the scene, they differentiate into
the throat, where they can be swallowed or expectorated (spit out). macrophages, large phagocytic cells that are able to devour
Chemical barriers to infection include the secretions of sebaceous as many as 100 pathogens and still survive. Some tissues,
(oil) glands in the skin, which contain chemicals that weaken or kill cer- particularly connective tissue, have resident macrophages
tain bacteria on the skin. As perspiration evaporates, the concentrated that routinely act as scavengers—devouring old blood cells,
salt on the skin helps prevent infection. Further, perspiration, saliva, bits of dead tissue, and other debris. Macrophages also
and tears contain an antibacterial enzyme called lysozyme. Saliva also release colony-stimulating factors, chemicals which pass by
helps to wash microbes off the teeth and tongue. Similarly, as urine is way of the blood to the red bone marrow. There, the factors
voided from the body, it flushes bacteria from the urinary tract. The stimulate the production and the release of white blood cells,
acidic pH of the stomach inhibits bacterial growth or kills many types primarily neutrophils.
Skin
Figure 13.3 Steps of the inflammatory reaction. (1) When there is an injury, tissue cells and mast cells release inflammatory
chemicals (such as histamine) that dilate blood vessels and cause them to leak. More blood flows to the area, and the skin appears red
and feels warm. (2) Because capillaries are more permeable, edema forms. Swelling and inflammatory chemicals stimulate pain recep-
tors (free nerve endings). (3) Blood clotting seals off the capillary, preventing blood loss and walling off the inflamed area. (4) Mono-
cytes (which become macrophages) and neutrophils squeeze through the capillary wall, and phagocytosis begins. (5) Monocytes
transform to macrophages, which stimulate specific immune responses in addition to destroying pathogens.
First Line: Nonspecific Mechanical barriers Intact skin, mucous membranes, respiratory cilia prevent entry
Chemical barriers Stomach acid, saliva, tears, etc., destroy and/or wash away pathogens
Normal flora of microbes Create a hostile environment for pathogens
Second Line: Nonspecific Inflammatory reaction Walls off infection site, draws white cells to area, signals a pain response
Nonspecific phagocytic cells Neutrophils, eosinophils, monocytes/macrophages engulf and destroy
invaders; basophils/mast cells produce chemicals to stimulate immune
response
Natural killer cells Kill pathogens by cell-to-cell contact
Protective proteins Complement participates, enhances defensive response. Interferon
interferes with viral replication
Third Line: Specific B lymphocytes Antibody response
T lymphocytes Produce messenger cytokines, stimulate B cells, direct cell destruction
Immunity usually lasts for some time. For example, once a Structure and Function of Antibodies
child has been properly immunized against measles virus, the
immune system confers a long-term protection (see the Medical The basic unit that composes antibody molecules is a Y-shaped
Focus on pages 309–310). Booster immunizations help to maintain protein molecule with two arms. Each arm has a “heavy” (long)
immunity throughout the teen years and into adulthood. polypeptide chain and a “light” (short) polypeptide chain (see
Immunity is primarily the result of the action of the Fig. 13.4). These chains have constant regions, located at the trunk of
B lymphocytes and the T lymphocytes. Recall that B lympho- the Y, where the sequence of amino acids is set. The class of antibody
cytes mature in the bone marrow,1 and T lymphocytes mature in for each individual molecule is determined by the structure of the
the thymus gland. B lymphocytes, also called B cells, give rise to antibody’s constant region. The variable regions form an antigen-
plasma cells, which produce antibodies. Antibodies combine with binding site, and their shape is specific to a particular antigen. The
and neutralize foreign antigens. Each antibody protein is shaped antigen combines with the antibody at the antigen-binding site in a
like a specific antigen and combines with that antigen in a pre- lock-and-key manner. Antibodies may consist of single Y-shaped
cise, “lock-and-key” fit (Fig. 13.4). These antibodies are secreted molecules called monomers, or they can be paired together in a mol-
into the blood, lymph, and other body fluids. In contrast, T lym- ecule called a dimer. Very large antibodies belonging to the M class
phocytes, also called T cells, do not produce antibodies. Instead, are pentamers—clusters of five Y-shaped molecules linked together.
certain T cells directly attack cells that bear nonself proteins. Other The antigen-antibody reaction can take several forms. Anti-
T cells regulate the immune response by producing cytokines, bodies react with viruses and toxins (the poisons made by bacteria)
which are proteins that regulate the immune response. by coating them completely—a process called neutralization. Other
antibodies cause agglutination, a reaction that produces an immune
1
Historically, the B stands for bursa of Fabricius, an organ in the chicken where these cells complex. An immune complex is a clump of antigens combined with
were first identified. antibodies. Clustering antigens into an immune complex marks the
Classes of Antibodies
There are five different classes of circulating antibody proteins, or
immunoglobulins (Igs) (Table 13.2). IgG antibodies are the major
type in blood, and lesser amounts are also found in lymph and
a tissue fluid. IgG antibodies bind to pathogens and their toxins.
IgG antibodies can cross the placenta from a mother to her fetus,
so that the newborn has a temporary, partial immune response.
As mentioned previously, IgM antibodies are pentamers. These
Activation cytokines from T cells antibodies are “first responders”: the first antibodies produced
by a newborn’s body. Subsequently, IgM antibodies are the first
to appear in blood soon after an infection begins and the first to
disappear before the infection is over. They are good activators of
the complement system. IgA antibodies are monomers or dimers
containing two Y-shaped structures. They are the main type of
antibody found in body secretions: saliva, tears, mucus, and breast
Clonal expansion
milk. IgA molecules bind to pathogens and prevent them from
b
reaching the bloodstream. The main function of IgD molecules
seems to be to serve as antigen receptors on immature B cells. IgE
antibodies are responsible for prevention of parasitic infections, but
antibody they can also cause immediate allergic responses.
Figure 13.5 Clonal selection theory as it applies to B cells. IgE Antibody type found as Responsible for
antigen receptors immediate allergic
(a) Each B cell has different antigen receptors. (b) An antigen combines
on basophils in response and
with only one B-cell receptor. Cytokines cause the B cell to multiply. blood and on mast protection against
(c) The chosen B cell forms plasma cells, which undergo apoptosis when cells in tissues certain parasitic
the immune response is complete. Memory B cells remain in the body. infections
T cell
activation
MHC/HLA protein
(self antigen)
b
antigen-presenting cell
foreign antigen
Clonal expansion
c
Cytotoxic T cell
T Cells and Cell-Mediated Immunity major histocompatibility complex (MHC) protein in the APC
When T cells leave the thymus, they have unique antigen recep- cell’s plasma membrane (Fig 13.6b).
tors just as B cells do (Fig. 13.6a). Unlike B cells, however, T Human MHC proteins are called HLA (human leukocyte
cells are unable to recognize an antigen present in lymph, blood, antigens). These proteins are found on all of the body’s cells.
or the tissues without help. The antigen must be presented to them Thousands of different genes that code for these proteins have been
by an antigen-presenting cell (APC). APCs can be specialized identified. Each individual human being has a unique combination of
macrophage cells or B lymphocytes. When an APC presents a viral genes, and thus, a unique set of HLAs. No two sets are exactly alike.
or cancer cell antigen to the T cell, the antigen is first linked to a An exception is the set belonging to monozygotic, or identical twins.
cytotoxic T cell
a nonself antigen
target cell
Tc cells
Cytotoxic T cell
vesicle
digesting enzyme
target cell
perforin
b
Perforin c
forms hole
in target cell. Digesting enzymes
enter through the
hole and cause
target cell to
Target cell undergo apoptosis.
d. Scanning electron micrograph SEM 1,2503
Figure 13.7 Cell-mediated immunity: How a cytotoxic T cell destroys a virus-infected or cancer cell. (a) The activated T cell
binds with a nonself antigen presented by the foreign cell. (b) The T cell releases perforin molecules, which form pores in the target cell
membrane. (c) Digesting enzymes enter through the hole, triggering apoptosis in the target cell. (d) This scanning electron micrograph
shows cytotoxic cells destroying a cancer cell.
Monoclonal Antibodies
Every plasma cell derived from the same B cell secretes antibodies
against one specific antigen. These are monoclonal antibodies
because all are the same type and because they are produced by
plasma cells derived from the same B cell. One method of producing
cancerous
hybridoma cell myeloma cell
monoclonal
antibody
Acquired immunodeficiency syndrome (AIDS) is caused by a of blood or greater (Fig. 13A). For a period of time after the initial
group of related retroviruses known as HIV (human immunodefi- infection with HIV, people don’t usually have any symptoms at all. A
ciency viruses). There are two forms of the virus, termed HIV-1 and few (1–2%) do have mononucleosis-like symptoms that may include
HIV-2. In the United States, AIDS is usually caused by HIV-1. Both fever, chills, aches, swollen lymph nodes, and an itchy rash. These
virus forms enter a host by attaching to a cell membrane receptor symptoms disappear, however, and no other symptoms appear for
called a CD4 receptor. HIV infects helper T cells, the type of lympho- quite some time. Although there are no symptoms, the person is
cyte that stimulates B cells to produce antibodies and cytotoxic T cells highly infectious. Despite the presence of a large number of viruses in
to destroy virus-infected cells. Macrophages, which present antigens the plasma, the HIV blood test is not yet positive because it tests for
to helper T cells and thereby stimulate them, are also under attack. the presence of antibodies and not for the presence of HIV itself. This
Other cells that have CD4 receptors can also be infected and later means that HIV can still be transmitted before the HIV blood test is
destroyed. positive.
HIV is a retrovirus, meaning that its genetic material consists of Several months to several years after a nontreated infection, the
RNA instead of DNA. Once inside the host cell, HIV uses a special individual will probably progress to category B, in which the helper
enzyme called reverse transcriptase to make a DNA copy (called T-lymphocyte count is 200 to 499 per mm3. During this stage, the
cDNA) of its genetic material. Next, cDNA integrates into a host patient may experience swollen lymph nodes in the neck, armpits, or
chromosome, where it directs the production of more viral RNA. Each groin that persist for three months or more. Other symptoms that indi-
strand of viral RNA causes the synthesis of an outer protein coat cate category B are severe fatigue not related to exercise or drug use;
called a capsid. The viral enzyme protease is necessary to the forma- unexplained persistent or recurrent fevers, often with night sweats;
tion of capsids. Capsids assemble with RNA strands to form viruses, persistent cough not associated with smoking, a cold, or the flu; and
which bud from the host cell and spread to other cells. persistent diarrhea.
The development of non-life-threatening but recurrent infections
Transmission of AIDS is a signal that the disease is progressing. One possible infection is
HIV is transmitted by contact with infected body fluids: semen, blood, thrush, a fungal infection that is identified by the presence of white
saliva, breast milk, vaginal fluid, and/or tissue fluid from an open spots and ulcers on the tongue and inside the mouth. The fungus may
wound. also spread to the vagina, resulting in a chronic infection there.
The most common method of transmission involves sexual con- Another frequent infection is herpes simplex, with painful and persis-
tact with an infected person, including vaginal or rectal intercourse tent sores on the skin surrounding the anus, the genital area, and/or
and oral/genital contact. Also, needle-sharing among intravenous the mouth.
drug users is high-risk behavior. Babies born to HIV-infected women Without treatment, the majority of infected persons proceed to
may become infected before or during birth, or through breast-feeding category C, in which the helper T-lymphocyte count is below
after birth. The rise in the incidence of AIDS among women of repro- 200 per mm3 and the lymph nodes degenerate. The patient is now
ductive age is paralleled by a rise in the incidence of AIDS in children suffering from AIDS, characterized by severe weight loss and
younger than age 13. weakness due to persistent diarrhea and coughing, and will most
To date, an estimated 100 million people worldwide have con- likely contract an opportunistic infection. An opportunistic infection
tracted HIV, and almost 39 million have died. A new infection is is one that only has the opportunity to occur because the immune
believed to occur every 15 seconds, the majority in heterosexuals. system is severely weakened. Such infections are extremely rare in
HIV infections are not distributed equally throughout the world. Most healthy individuals. Persons with AIDS die from one or more oppor-
infected people live in Africa (70%) where the infection first began, tunistic diseases, such as Pneumocystis jirovecii pneumonia, tubercu-
but new infections are now occurring at the fastest rate in Southeast losis, toxoplasmic encephalitis, Kaposi’s sarcoma, or invasive cervical
Asia and the Indian subcontinent. cancer. This last condition has been added to the list because the
incidence of AIDS has now increased in women.
Phases of an HIV Infection
The Centers for Disease Control and Prevention recognize three Treatment for AIDS
stages of an HIV-1 infection, called categories A, B, and C. During Treatment for AIDS is termed highly active antriretroviral therapy, or
the category A stage, the helper T-lymphocyte count is 500 per mm3 HAART. This therapy consists of combining three or more categories
—Continued
107
Category A: Acute Phase Category B: Chronic Phase Category C: AIDS
1100
CD4 T Lymphocyte in Blood (per mm3)
1000
106
900
600
500 104
400
300
HIV 103
200
100
102
0 1 2 3 4 5 6 7 8 9 10
Years Since Infection
Figure 13A Stages of an HIV infection. In category A individuals, the number of HIV in plasma rises upon infection and then
falls. The number of CD4 T lymphocytes falls, but stays above 400 per mm3. In category B individuals, the number of HIV in
plasma is slowly rising, and the number of T lymphocytes is decreasing. In category C individuals, the number of HIV in plasma
rises dramatically as the number of T lymphocytes falls below 200 per mm3.
of drugs. Currently, four categories exist: (1) drugs that inhibit viral of infection worldwide (see Chapter 17 Medical Focus: Prevention of
entry into the cell; (2) drugs that inhibit the reverse transcriptase STIs for details). Counseling of pregnant women is essential to pre-
enzyme; (3) drugs to inhibit protease, an enzyme needed for forma- vent mother-to-child HIV transmission.
tion of a viral capsid; (4) drugs that prevent integration of the viral The likelihood of transmission can be lessened if the pregnant
RNA into human DNA. This multidrug therapy, when taken accord- mother takes a modified form of HAART, and if the child is deliv-
ing to the manner prescribed, can often effectively reduce detectable ered by cesarean section. The mother also must not breast-feed her
blood HIV and restore concentrations of CD4 cells to normal or near- child because the virus is transmissible in breast milk. Medical and
normal levels. The sooner drug therapy begins after infection, the dental professionals should carefully follow universal precautions
better the chances that the immune system will not be destroyed by against infection (gloves, surgical masks, proper disinfection tech-
HIV. Also, HAART medication must be continued indefinitely. How- niques, etc.).
ever, it’s important to note that HAART does not cure AIDS, and all Many investigators are working on a vaccine for AIDS. Some are
of the medications potentially have very serious side effects. These trying to develop a vaccine in the traditional way. Others are working
include bone and joint destruction, heart attack, liver damage, and on subunit vaccines that utilize just a single HIV protein as the vac-
anemia. Unfortunately, a patient’s strain of HIV may become resistant cine. So far, no method has resulted in creating sufficient antibodies
to HAART over time. to keep an infection at bay. After many clinical trials, none too suc-
At present, the best strategy to slow the AIDS epidemic focuses cessful, most investigators now agree that a combination of various
on infection prevention. Education regarding safe sex practices, espe- vaccines may be the best strategy to bring about a response in both B
cially proper condom use and abstinence, has already reduced the rate lymphocytes and cytotoxic T cells.
Immunization protects children and adults from diseases. The success effects (which occur rarely), or can’t bear the expense. As a result,
of immunization is witnessed by the fact that the smallpox vaccination preventable diseases have recently come roaring back: a major out-
is no longer required because the disease has been eradicated. How- break of measles in 2014 spread throughout 14 states and sickened
ever, parents today often fail to get their children immunized because over 600 people. This was the greatest number of cases since 2000,
they don’t realize the importance of immunizations, fear potential side when it was thought that measles had been eliminated in the
Zoster 1 Dose
after
age 60
* for children or adolescents not previously immunized as infants
**optional, not necessary if doses 1 and 2 have been administered previously
***optional, not necessary if three doses administered previously
‡ recommended if some risk factor is present (e.g., medical condition, occupation, lifestyle).
D for persons with no prior immunity
Figure 13B Suggested immunization schedule for infants, young children, and adolescents. Children who are immune-
compromised may need additional immunizations. Always consult with your health-care provider for up-to-date information on
recommended immunizations for your area.
Source: Centers for Disease Control and Prevention. Recommended immunization schedules for persons aged 0–18 years—United States, 2015.
—Continued
United States. Pertussis (whooping cough), mumps, and chickenpox exposure to these viruses warrants vaccination early in life. Infants
have also made a comeback in children and adults. now receive their first dose of HBV vaccine before leaving the hos-
Figure 13B shows a recommended immunization schedule for pital, with booster immunizations at approximately 3 months and
children and adults. The United States is now committed to the goal of 12 months of age.
immunizing all children against the common types of childhood dis- Cervical cancer has recently been linked to the occurrence of
eases listed. Diphtheria, whooping cough, Haemophilus influenzae, genital warts, a sexually transmitted disease caused by human papil-
and Pneumococcus infection are all life-threatening respiratory dis- lomavirus (HPV). Therefore, a new vaccine for papillomavirus type
eases. Tetanus is characterized by muscular rigidity, including a 16, the most frequent cause of genital warts, has been developed.
locked jaw. These extremely serious infections are all caused by bac- Currently, the U.S. Centers for Disease Control recommends three
teria; the rest of the diseases listed are caused by viruses. Varicella doses of human papillomavirus vaccine for young women between
virus causes chickenpox. Polio is a type of paralysis; measles and the ages of 9 and 18, and also for young men 9 to 21 years old. Perhaps
rubella, sometimes called German measles, are characterized by high more vaccines for sexually transmitted diseases will one day become
fever and skin rashes; and mumps is characterized by fever and available.
enlarged parotid and other salivary glands. Rotavirus causes a severe It’s important to note that the need for immunizations and
diarrheal illness, which can be fatal in infants and small children. boosters doesn’t stop with adolescence. Regular boosters for teta-
Further, each one of these illnesses can cause fatal complications, nus and diptheria are recommended every 10 years for adults.
though the incidence is rare. Further, everyone should get a yearly flu shot, beginning at age
Currently, immunizations for two forms of hepatitis viruses is 6 months.
recommended. Hepatitis A virus (HAV) is transmitted by contami- Even though most bacterial infections (e.g., tetanus) can be cured
nated water and food, especially raw shellfish. Hepatitis B virus by antibiotic therapy, it’s far better to be immunized. Some patients
(HBV) is a blood-borne pathogen that is spread in the United States develop allergic reactions to antibiotics, which can be fatal. In addi-
mainly by sexual contact and intravenous drug use. Health-care tion, antibiotics kill beneficial bacteria as well as those that cause
workers who are exposed to blood or blood products are also at risk, disease. These beneficial bacteria may have checked the spread of
and maternal-neonatal transmission is a possibility as well. Both of pathogens that now are free to multiply and to invade the body. This is
these viruses can cause a serious acute infection. However, HBV why antibiotic therapy is often followed by a secondary infection,
infection can also lead to chronic hepatitis and then cancer of the such as a vaginal yeast infection in women. Likewise, a serious diar-
liver. It is relatively common for children to come into contact with rheal illness caused by a bacterium called Clostridium difficile (or
HAV, but rare for a child to come into contact with hepatitis B virus. “C-diff,” as it is called by heath-care workers) often follows antibiotic
However, physicians feel that the potential for liver damage from use, especially in the elderly.
Antibiotic abuse also leads to resistant bacterial strains that
are difficult to cure. For example, a once-harmless skin bacterium
called Staphylococcus aureus now causes thousands of life-
threatening infections and deaths every year. Post-surgical patients
are particularly at risk, but anyone who is hospitalized can become
infected. After decades of antibiotic exposure, this microbe (abbre-
viated MRSA, for methicillin-resistant Staphylococcus aureus)
and others have become resistant to all but the strongest
antibiotics.
Therefore, everyone should take advantage of appropriate vac-
cinations. Preventing a disease by becoming actively immune to it is
certainly preferable to becoming ill and needing antibiotic therapy
to be cured. Vaccination also benefits all of society by preventing
the spread of disease to the most vulnerable among us: newborns
and infants, the elderly, and those whose immune systems are
weakened.
“Over there, over there, Send the word, send the word over there— elderly and infirm. In June 2009, the World Health Organization
That the Yanks are coming, The Yanks are coming . . . And we won’t declared the H1N1 swine flu outbreak to be a global pandemic. For-
come back till it’s over, Over there!” tunately, the pandemic persisted for only about a year.
—“Over There,” George M. Cohan In recent studies, scientists reconstructed the 1918 ancestor virus
using genetic engineering, then compared its disease-causing ability to
In April 1918, American soldiers who proudly marched off to World that of modern-day swine flu H1N1. The results were staggering: the
War I battlefields “over there” (referring to Europe, in the words of the Spanish flu virus is roughly 39,000 times more virulent than the newer
popular patriotic ballad of the time), took an unwanted hitchhiker with H1N1 strains that now exist. That’s good news for us as a species, because
them—a particularly virulent strain of influenza A, nicknamed the it seems to indicate that the viral mutants have grown weaker over time.
“Spanish Flu” because of the huge numbers of victims in that country. However, the possibility of deadly antigenic shift will always remain. As
It quickly became a worldwide epidemic, or pandemic, causing an esti- we humans continue to travel the world more and more easily, we’ll take
mated 50 million deaths. Among the soldiers, Spanish flu caused twice our viruses (and those of our native animals) with us. If rapid genetic
as many deaths as those that resulted from combat. This particularly changes occur, new viral strains could spread efficiently from person to
savage virus is once again a concern because of characteristics it shares person, and another pandemic could happen. However, thanks to modern
with a modern-day virus: influenza A (H1N1), the so-called “swine technology, we’ll have a few more weapons in our antiviral arsenal than
flu” virus, which surfaced and rapidly became pandemic in 2009. our great-grandparents had back in 1918. During the 2009 pandemic,
Influenza viruses, like all viruses, have two basic parts. The core of communication tools like radio, television, and the Internet enabled pub-
the virus is its genetic material, which can be either DNA or RNA. Influ- lic health officials all over the world to organize their efforts to fight this
enza A viruses are RNA viruses (Fig. 13C). Like the HIV virus (see new influenza. Preventive vaccinations were quickly prepared, and drugs
Medical Focus, pp. 307–308), their genetic material is covered by a pro- that prevent viral replication, and antibiotics for secondary infections
tective protein coat called a capsid. An additional third piece, called the (such as pneumonia ) were available for treatment. Researchers continue
lipid envelope, contains protein spikes that allow the virus to attach to its to work on ways to better anticipate and recognize viral antigenic shift, so
own specific kind of host cell and not another nonmatching kind. The two we can stay one step ahead of our influenza viruses.
types of protein spikes, abbreviated H (for hemagglutinin) and N (for In the meantime, your best approach to avoid influenza is to use
neuraminidase), allow each type of influenza virus to be categorized. common sense. Get your flu shot every fall, because each new vaccination
There are 16 known types of H proteins, and 9 known types of N proteins. is tailored to that season’s viruses. Wash your hands often and well, don’t
Thus, many different combinations are possible, meaning there are many touch your nose or eyes (because virus can enter your body when you do),
different ways for viruses to attach to different kinds of host cells. Each and stay away from sick people. To keep from infecting others if you do
different combination of H and N represents a new form of flu virus. get sick, don’t go out in public. Cough or sneeze into tissues or your
Avian influenza A, the “bird flu,” which emerged in 1997 and again in sleeve, and wash your hands before you touch anything. Further, if you do
2006, is designated H5N1. The original Spanish flu virus is denoted develop severe flu symptoms such as difficulty breathing, extremely high
H1N1, and the swine flu virus is its molecular “grandchild.” fever, or chest pain, seek prompt medical attention. Antiviral drugs have
How do these new viruses emerge? It’s well known that the genetic the best chance to successfully treat you if you seek help quickly.
material of influenza virus has an extremely high mutation rate. A phe-
nomenon called antigenic drift causes small changes in flu viruses, and
explains why each year a new and different flu shot is needed. By contrast,
hemagglutinin
antigenic shift is a major change that occurs very infrequently (between 10
neuraminidase
and 40 years during the last century). Some of these mutations affect the
structure of the protein spikes, so that a virus that previously could only envelope
infect a particular animal can “jump species.” As the virus moves from RNA
one animal to the next, it can also swap genetic material and create new
combinations. Scientists studying the ancestor H1N1 from 1918 have
noted that it probably originated as a “bird flu” virus, which then mutated spike
to infect human beings. Modern H1N1 flu virus contains bird, human, and
swine DNA—and the swine DNA is from both Europe and Asia. Scien- capsid
tists call this four-way mutant a “quadruple reassortant” virus. The radical
changes of an antigenic shift are what cause pandemics, because human
populations have little or no immunity to a dramatically changed virus.
In 2009, public health officials were particularly concerned
because the illness caused by H1N1 virus was eerily reminiscent of
the 1918 Spanish flu epidemic. As in 2009, the original pandemic Figure 13C Influenza A virus is an RNA virus. It has
protein spikes on its outer envelope that make it specific
first began in the spring, not in the winter like most new viral illnesses.
to one kind of host cell.
Both forms killed healthy young adults and children, not just the
It’s a fact that few of us appreciate: Autoimmune disease is approach- Enter swine whipworm, Trichuris suis, a lowly parasitic worm
ing epidemic levels. It’s the second-leading cause of chronic illness in that normally infects pigs. Clinical researchers have chosen the
the United States, and over 50 million Americans suffer from at least eggs, or ova, as the agent for helminthic therapy. This unusual (and
one autoimmune disease. Further, the incidence of autoimmune dis- some would say, downright weird) treatment involves deliberately
eases has risen dramatically in the entire Western world over the past infecting people with parasites to create a counteractive immune
several decades, and research continues to show that many illnesses response that appears to calm the inflammation that causes autoim-
have an autoimmune link. Scientists have long suspected that autoim- mune disease. There are many human parasitic organisms, but
mune disease results from excessive cleanliness—the so-called Trichuris suis ova (TSO) are the parasite of choice because they
“hygiene hypothesis.” These researchers argue that because sanitation can’t reproduce in the human intestinal tract, so they don’t normally
has eliminated exposure to microbes, the immune system is not prop- infect humans. Subjects drink a solution containing TSO, and the
erly regulated. As a result, lymphocytes produce T1 cell cytokines, a eggs hatch in the intestine and latch onto its wall. There, they prompt
form that attacks body cells. In effect, an immune system that is production of T2 cell cytokines, which create a separate immune
poorly challenged by pathogens attacks and destroys body cells and response, and in turn, diminish the inflammatory responses of auto-
tissues instead. Therapy for any one of these many disorders can be immune disease. After approximately two weeks, TSO die and are
complicated and tricky, because each is a separate disease. Tradi- excreted. Clinical trials continue to show success in the treatment of
tional treatments that suppress or eliminate the immune response can Crohn’s disease and ulcerative colitis using TSO, and more studies
create fatal complications, including infections and cancer. are planned.
Immune Deficiency 13. Which term describes the amount of antibody present in a
blood plasma sample?
When a person has an immune deficiency, the immune system is un-
a. booster c. hematocrit
able to protect the body against disease. AIDS (see the Medical Focus
on pages 307–308) is an example of an acquired immune deficiency. As b. vaccine d. titer
a result of a weakened immune system, AIDS patients show a greater Answers in Appendix A.
susceptibility to a variety of diseases, and they also have a higher risk of
cancer. Immune deficiency may also be genetic (that is, inherited from
one’s parents) or congenital (due to failure of lymphatic tissue to de- 13.5 Effects of Aging
velop). For example, in some infants the thymus gland fails to develop, 10. Describe the anatomical and physiological changes that occur in the
producing a child with severe immune deficiency. Infrequently, a child immune system as we age.
may be born with an impaired B- or T-cell system caused by a defect
in lymphocyte development. In severe combined immunodeficiency With advancing age, people become more susceptible to all types of
disease (SCID), a genetic disorder, both antibody and cell-mediated infections and disorders because the immune system exhibits lower
immunity are lacking or inadequate. Without treatment, even common levels of function. One reason is that the thymus gland degenerates.
infections can be fatal. Replacing defective stem cells with healthy ones Having reached its maximum size in early childhood, it begins to
through bone marrow transplantation can often produce a cure. shrink after puberty and has virtually disappeared by old age. As
the gland decreases in size, so does the number of T cells. The T
Content CHECK-UP! cells remaining do not respond to foreign antigens; therefore, the
chance of having cancer also increases with age.
11. Which of the following is a form of active immunity?
Among the elderly, the B cells sometimes fail to form clones. Other
a. transfer of antibodies from mother to fetus across B cells may form clones, but the antibodies released may not function
the placenta
well. Therefore, infections are more common among the elderly. In
b. transfer of antibodies from mother to baby in breast milk addition, the antibodies of older people are more likely to attack the
c. immunization for hepatitis B virus body’s own tissues, increasing the incidence of autoimmune diseases.
d. gamma globulin injection for hepatitis B virus The response of elderly individuals to vaccines is decreased.
12. Describe the two forms of passive immunity: natural and However, considering that their overall level of immune response
artificial. How is each one obtained? Is this form of immune is low, it is better that these people be vaccinated than not. For this
response as effective or long-lasting as active immunity? Why reason, elderly individuals are encouraged to get an influenza (flu)
or why not? vaccination each year.
Summary
13.1 Lymphatic System A. Nonspecific defenses include activated T cells undergo apopto-
The lymphatic system consists of lym- barriers to entry, the inflamma- sis. A few cells remain, however,
phatic vessels and lymphatic organs. tory reaction, nonspecific white as memory T cells. Cytokines, in-
A. The lymphatic vessels return ex- blood cells, natural killer cells, cluding interferon and interleukins,
cess tissue fluid to the blood- and protective proteins. are used in an attempt to promote
stream, absorb fats at intestinal B. Specific defenses require B lym- the body’s ability to recover from
villi, and help the immune system phocytes and T lymphocytes, cancer and to treat AIDS.
defend the body against disease. also called B cells and T cells. B 13.4 Creating an Immune Response
B. Lymphatic capillaries have thin cells undergo clonal selection A. Immunity can be induced in
walls. Larger vessels are structured with production of plasma cells various ways. Vaccines are avail-
the same as cardiovascular veins, and memory B cells after their able to induce long-lasting, ac-
with valves that prevent backward antigen receptors combine with tive immunity.
flow. The largest lymphatic ves- a specific antigen. Plasma cells B. Antibodies sometimes are avail-
sels, called the right lymphatic duct secrete antibodies and eventu- able to provide an individual with
and thoracic duct, return blood to ally undergo apoptosis. Plasma temporary, passive immunity.
the right and left subclavian veins. cells are responsible for anti- C. Monoclonal antibodies are pro-
13.2 Organs, Tissues, and Cells of the body-mediated immunity. Anti- duced in the laboratory and used for
Immune System bodies are Y-shaped molecules diagnosis and treatment purposes.
Lymphocytes are produced and ac- with two binding sites for a spe- D. Allergic responses occur when the
cumulate in the lymphatic organs. cific antigen. Memory B cells re- immune system reacts vigorously to
A. The primary lymphatic organs main in the body and produce substances not normally recog-
are the red bone marrow, where antibodies if the same antigen nized as foreign. IgE-mediated or
blood cells are produced, and enters the body at a later date. immediate allergic responses, usu-
the thymus, which houses and C. T cells are responsible for cell- ally consisting of coldlike symp-
matures T lymphocytes. mediated immunity. The two main toms, are due to the activity of
B. The secondary lymphatic organs types of T cells are cytotoxic T antibodies. T-cell mediated allergic
include the spleen, lymph nodes, cells and helper T cells. Cytotoxic responses, such as contact dermati-
tonsils, Peyer patches, and ap- T cells kill virus-infected or cancer tis, are due to the activity of T cells.
pendix. Lymph is cleansed of cells on contact because they E. Autoimmune responses occur
pathogens and/or their toxins in bear a nonself antigen. Helper T when immune system cells
both lymph nodes and spleen, cells produce cytokines and stimu- mistakenly attack body tissues
and blood pathogens are de- late other immune cells. Like B and organs. Myasthenia gravis,
stroyed in the spleen. cells, each T cell bears antigen re- multiple sclerosis, and rheumatoid
C. T lymphocytes mature in the thy- ceptors. However, for a T cell to arthritis are a few of the many
mus, while B lymphocytes ma- recognize an antigen, the antigen autoimmune diseases.
ture in the red bone marrow, must be presented by an F. Immune system deficiencies can
where all blood cells are pro- antigen-presenting cell (APC), usu- be acquired, such as AIDS, or
duced. White blood cells are ally a macrophage, in the groove genetic, such as SCID.
necessary for both nonspecific of an HLA (human leukocyte anti- 13.5 Effects of Aging
and specific defenses. gen). Thereafter, the activated T The thymus gets smaller as we age, and
13.3 Nonspecific and Specific Defenses cell undergoes clonal expansion fewer antibodies are produced. The
Immunity involves nonspecific and until the illness has been elderly are at great risk of infections,
specific defenses. stemmed. Then most of the cancer, and autoimmune diseases.
Study Questions
1. What is the lymphatic system, and what sible for which type of immunity? 11. How are monoclonal antibodies pro-
are its three functions? (p. 294) (p. 301) duced, and what are their applications?
2. Describe the structure and the function 6. Describe the structure of an antibody, (pp. 306, 312)
of red bone marrow, the thymus, the and define the terms variable regions 12. Discuss allergies, tissue rejection, and
spleen, lymph nodes, and the tonsils. and constant regions. (pp. 301–302) autoimmune diseases as they relate to
(pp. 294–298) 7. Describe the clonal selection theory as the immune system. (p. 312)
3. What are the body’s nonspecific de- it applies to T cells. (pp. 303–304) 13. Explain the different causes for immune
fense mechanisms? (pp. 298–300) 8. Name the two main types of T cells and deficiency diseases, and describe their
4. Describe the inflammatory reaction and state their functions. (pp. 304–305) effects. (pp. 307–308, 313)
give a role for each type of cell and 9. What are cytokines and how are they 14. How do the lymphatic and immune
molecule that participates in the reac- used in immunotherapy? (p. 305) systems help maintain homeostasis?
tion. (pp. 298–300) 10. How is active immunity artificially (pp. 314–315)
5. What is the clonal selection theory as achieved? How is passive immunity 15. How does the skeletal system assist
it applies to B cells? B cells are respon- achieved? (pp. 305–306) the immune system in maintaining
homeostasis? (pp. 314–315)
Learning Outcomes After you have studied this chapter, you should be able to:
14.1 The Respiratory System 14.3 Gas Exchange and Transport 14.6 Homeostasis
1. Describe the events that occur 7. Describe the process of gas 12. Describe how the respiratory system
during respiration. exchange in the lungs and the works with other systems of the
2. Describe the structure and function tissues. body to maintain homeostasis.
of the respiratory system organs. 8. Explain how oxygen and carbon
3. Explain the structure and importance dioxide are transported in the blood. I.C.E.—In Case of Emergency
of the respiratory membrane. Lung Collapse
14.4 Respiration and Health
14.2 Mechanism of Breathing 9. Name and describe the various Medical Focus
4. Outline the process of ventilation, infections of the respiratory tract. The Most-Often-Asked Questions About
including inspiration and expiration. 10. Describe the effects of smoking on Tobacco and Health
5. Describe vital capacity and its the respiratory tract and on overall
relationship to other measurements health. What’s New
of breathing capacity. Bronchial Thermoplasty: A Surgical Treatment
6. Tell where the respiratory center is 14.5 Effects of Aging for Asthma
located, and explain how it controls 11. Describe the anatomical and
the normal breathing rate. physiological changes that occur in Human Systems Work Together
the respiratory system as we age.
Respiratory System
318
Nasal cavity
filters, warms, and moistens air
Pharynx
passageway where pathway
for air and food cross
Upper Glottis
Respiratory space between the vocal cords;
Tract opening to larynx
Larynx
(voice box); produces sound;
covered by the epiglottis
during swallowing
Trachea
(windpipe); passage of air
to bronchi
Bronchus
passage of air to lungs
Bronchioles
passage of air to alveoli
Lower
Respiratory
Tract Lung
contains alveoli (air sacs);
carries out gas exchange
Diaphragm
Figure 14.1 The skeletal muscle; functions
respiratory tract. Note the struc- in ventilation
tures of the upper respiratory tract
and the lower respiratory tract.
The tract extends from the nasal
cavities to the lungs.
hyoid bone
fat
thyroid thyroid cartilage
cartilage false vocal cord
(Adam’s apple)
true vocal cord
base of tongue
epiglottis
tracheal tracheal cartilage vocal cords
cartilage
trachea
membranous membranous glottis
part of trachea part of trachea
cilia
mucus
goblet
cell
nucleus
basement
membrane
a. b.
cilia
goblet cell
Imagine that you’re a military medic who’s called upon to respond when burst as a result of the high pressure from the bomb blast, and air has
troops have been injured due to a bomb blast. As you arrive at the scene, filled his thorax from the hole in his lung. When the lungs collapse, the
two fallen soldiers need your attention. One has an open chest wound, air filling the chest compresses the heart and prevents it from filling
caused by shrapnel cutting his chest. The second was nearby when the with blood. This is termed tension pneumothorax, or air in the thorax.
blast occurred, but has no obvious wounds. Yet, both have the same You’ll need to act fast, or both victims will slip into shock.
symptoms: sharp pain when they inhale, difficulty speaking, and a feel- With the help of the first soldier’s buddies, you put a special
ing of breathlessness. Both soldiers’ blood pressure is low and pulse is airtight pressure bandage over his open chest wound, which will
rapid, indicating that they might slip into shock. You take a quick history prevent additional air from entering the wound and help stop bleeding.
from both victims and from their buddies. Next, you’ll start his intravenous solution (IV). By listening to the
Right away, you suspect each soldier has atelectasis—the second soldier’s chest with your stethoscope, you’ll be able to tell
technical term for a collapsed lung. As you’ll recall, the lungs are held where the lung has collapsed because it will sound hollow. When you
up against the chest wall by the attraction force of surface tension. If trained as a medic, you learned to do a thoracocentesis, and you’ll
air enters the thorax, surface tension will fail, and the lungs will rapidly insert a catheter between the soldier’s ribs to let the trapped air
collapse. The first soldier’s chest wound is allowing air from the out into the atmosphere. Now your patients are ready for their helicop-
atmosphere to enter the thorax. A section of the second soldier’s lung ter trip to a field hospital for more advanced care.
tube by way of an incision made in the trachea. This tube acts as of a lung, and the base is the inferior broad portion that curves
an artificial air intake and exhaust duct. The operation is called a to fit the dome-shaped diaphragm, the muscle of respiration that
tracheostomy. separates the thoracic cavity from the abdominal cavity. The lat-
eral surfaces of the lungs follow the contours of the ribs in the
The Bronchial Tree thoracic cavity.
Each lobe of the lung is further divided into lobules, and each
The trachea divides into right and left primary bronchi (sing.,
lobule has a bronchiole supplying many alveoli. Pulmonary ar-
bronchus), which lead into the right and left lungs (see Fig. 14.1).
teries travel alongside the bronchi; likewise, pulmonary arterioles
The primary bronchi then branch into secondary bronchi: one for
parallel the bronchioles. Each pulmonary arteriole then further
each lobe of the lung. Thus, there are three secondary bronchi for
branches to form pulmonary capillaries. Pulmonary capillaries
the right lung, which has three lobes. Two secondary bronchi sup-
surround and cover each alveolus of the lung. Elastic connective
ply the left lung, which has only two lobes in order to allow room
tissue binds the air passages to the blood vessels within each lung;
for the heart. Each secondary bronchus then divides into smaller
this elastic tissue helps the lungs return to their resting position, or
tertiary bronchi. These smaller bronchi are supported by smaller
recoil, when a person exhales.
plates of cartilage, in place of the cartilage rings of the trachea.
Each lung is enclosed by a double layer of serous membrane
Bronchioles are the smallest conducting airways. They lack carti-
called the pleurae (sing., pleura). The visceral pleura adheres to
lage support, but possess a ciliated epithelium and a well-developed
the surface of the lung; the parietal pleura lines the inside of the
smooth muscle layer. During an asthma attack, the smooth muscle
thoracic cavity. The pleurae produce a lubricating serous fluid
of the bronchioles contracts, causing bronchiolar constriction and
that reduces friction and allows the two layers to slide across one
characteristic wheezing. Each bronchiole leads to an elongated
another. Serous fluid, a water-based solution, also creates surface
space enclosed by a multitude of air pockets, or sacs, called alveoli
tension: the tendency for water molecules to cling to each other
(sing., alveolus). The components of the bronchial tree beyond the
(due to hydrogen bonding between the molecules) and to form a
primary bronchi, including the alveoli, compose the lungs.
droplet (see section 2.2). Surface tension holds the two pleural
layers together, thus holding the lungs open against the chest
The Lungs wall. If this surface tension force is disrupted, the lung will col-
The lungs are paired, cone-shaped organs. Each fills its own pleu- lapse, as described in the In Case of Emergency reading above.
ral cavity inside the thoracic cavity, separated by the mediasti-
num. Recall that the mediastinum is the central compartment that The Alveoli
separates the thoracic cavity. It contains the heart and its major With each inhalation, air passes through the bronchial tree to the
vessels, primary bronchi, thymus gland, trachea, and esophagus alveoli. An alveolar sac is made up of simple squamous epithe-
(see Chapter 1, page 7). The apex is the superior narrow portion lium surrounded by pulmonary capillaries. Gas exchange occurs
erythrocyte
pulmonary
capillaries
capillary
endothelial cell
respiratory basement
membrane membrane
alveolar
epithelial cell
alveolar
macrophages
surfactant-
secreting cells
lung
When When
pressure pressure
in lungs in lungs
rib cage
decreases, increases,
air comes air is
rushing in. pushed out.
a. Inspiration b. Expiration
Figure 14.7 Inspiration versus expiration. (a) During inspiration, the thoracic cavity and lungs expand so that intrapulmonary
pressure decreases. Now air flows into the lungs. (b) During expiration, the thoracic wall and lungs recoil, assuming their original
positions and pressures. Now air is forced out. The internal intercostal muscles only contract during forceful expiration.
lot harder than normal during and immediately after that heavy nose or mouth to the lungs and from the lungs to the nose or mouth
exercise. Maximum inspiratory effort involves the accessory is vitally important. Therefore, a technique has been developed
muscles of respiration: muscles of the back, pectoralis minor that allows physicians to determine if there is a medical problem
(chest), sternocleidomastoid muscles of the anterior neck, etc. that prevents the lungs from filling with air upon inspiration and
Their combined efforts can help to make the thoracic cavity larger releasing air from the body upon expiration. An instrument called
than normal, thus allowing maximum expansion of the lungs. a spirometer records the volume of air exchanged during normal
While inspiration is always the active phase of breathing, breathing and during deep breathing. A spirogram (recording from
expiration is usually passive—that is, the diaphragm and external a spirometer) shows the measurements recorded by a spirometer
intercostal muscles are simply allowed to relax, the lungs recoil, when a person breathes as directed by a technician (Fig. 14.8).
and expiration occurs. However, expiration can also be forced.
Forced expiration accompanies the maximum inspiratory efforts
of heavy exercise. Forced expiration is also necessary to sing, blow Respiratory Volumes and Capacities
air into a trumpet, or blow out birthday candles. Contraction of the Normally when we’re relaxed, only a small amount of air moves
internal intercostal muscles can force the rib cage to move down- in and out with each breath. This amount of air, called the tidal
ward and inward. In addition, when the abdominal wall muscles volume, is only about 500 ml.
(rectus abdominis, external and internal obliques, and transversus It is possible to increase the amount of air inhaled, and there-
abdominis) contract, they push on the abdominal organs, which are fore the amount exhaled, by deep breathing. The maximum volume
compressed upward against the diaphragm. This creates increased of air that can be moved in plus the maximum volume that can be
pressure in the thoracic cavity, which helps to forcefully expel air. moved out during a single breath is the vital capacity. It is called
During breathing, air moves into the lungs from the nose or vital capacity because your life depends on breathing, and the more
mouth (called inspiration, or inhalation), and then moves out of the air you can move, the better off you are. A number of different
lungs during expiration, or exhalation. A free flow of air from the illnesses, discussed in section 14.4, can decrease vital capacity.
inspiratory
4,800 reserve
volume inspiratory
Volume of Air in Lungs (ml)
capacity
vital
3,600 capacity
total
2,900 lung
tidal
capacity
2,400 volume
expiratory
reserve
volume
functional
1,200 residual
capacity
residual residual
volume volume
0
Breaths/Time
Figure 14.8 Vital capacity. A spirometer measures the amount of air inhaled and exhaled with each breath. During inspiration,
the tracing moves up, and during expiration, the tracing moves down. The volume of one normal breath (tidal volume) multiplied by the
number of breaths per minute is called the minute ventilation. A lower-than-normal minute ventilation can be a sign of pulmonary malfunc-
tion. Vital capacity (red) is the maximum amount of air a person can exhale after taking the deepest inhalation possible.
Vital capacity varies by how much we can increase inspiration be determined by adding expiratory reserve volume and residual
and expiration over the tidal volume amount. We can increase volume. The maximum amount of air that can be held in a person’s
inspiration by using the accessory muscles of respiration (ster- lungs is called the total lung capacity. This measure is the sum of
nocleidomastoid, pectoralis minor, etc.) to expand the chest, and all four volumes: tidal volume, expiratory reserve volume, inspira-
also by lowering the diaphragm to the maximum extent possible. tory reserve volume, and residual volume.
Forced inspiration usually increases the volume of air beyond the
tidal volume by 2,900 ml, and that amount is called the inspiratory
reserve volume. We can increase the amount of air expired by Control of Ventilation
contracting the abdominal and internal intercostal muscles. This Normally, adults have a breathing rate of 12 to 20 ventilations per
so-called expiratory reserve volume is usually about 1,400 ml of minute. The basic rhythm of ventilation is controlled by a primary
air. You can see from Figure 14.8 that vital capacity is the sum of respiratory center located in the medulla oblongata of the brain.
the tidal, inspiratory reserve, and expiratory reserve volumes. The primary respiratory center automatically sends out motor
It’s a curious fact that some of the inhaled air never reaches nerve signals by way of the phrenic nerve to the diaphragm. Simul-
the alveoli; instead, it fills the nasal cavities, trachea, bronchi, and taneously, the intercostal nerves stimulate the external intercostal
bronchioles (see Fig. 14.1). In an average adult, some 70% of the muscles of the rib cage (Fig. 14.9). When these muscles contract,
tidal volume does reach the alveoli, but 30% remains in the air- the thoracic volume and lung volume increase, and the person in-
ways. These passages are not used for gas exchange, and therefore hales. When the respiratory center stops sending neuronal signals
they are said to contain dead-space air. To ensure that a large por- to the diaphragm and the rib cage, the diaphragm relaxes, resum-
tion of inhaled air reaches the lungs, it is better to breathe slowly ing its dome shape. The rib cage moves down and in. Decreasing
and deeply. Also, note in Figure 14.8 that even after a very deep thoracic and lung volumes allow the person to exhale.
exhalation, some air (about 1,000 ml) remains in the alveoli; this The primary respiratory center allows the basic pattern of
is called the residual volume. This air is not as useful for gas inhalation and exhalation. However, if the medulla functions alone
exchange because it contains a great deal of CO2 and has been (as might occur in a person with a serious head injury, if nerves
depleted of oxygen. In some lung diseases, such as emphysema, from higher centers are damaged), respiration is short and gasping.
the residual volume increases because the individual has difficulty Breathing rhythmically at a normal rate and volume requires nervous
emptying the lungs. This means that the vital capacity is reduced input from the pons, the brain stem center immediately superior to
because the lungs have more residual volume. the medulla. Functioning together, these two brain centers allow
With further study of Figure 14.8, you can see that the four normal, quiet breathing, a pattern referred to as eupnea: smooth,
respiratory capacities are sums of the four respiratory volumes. sustained inspiration, followed by a smooth, sustained expiration.
Inspiratory capacity is the sum of inspiratory reserve volume and Although the respiratory center controls the rate and depth
tidal volume; likewise, expiratory capacity is the sum of expiratory of breathing, its activity can be influenced by nervous input and
reserve volume and tidal volume. Functional residual capacity can chemical input.
Content CHECK-UP!
Figure 14.9 Nervous control of breathing. During 4. Name the muscles that contract when a person inhales.
inspiration, respiratory control areas of the pons and medulla 5. Which of the following has to be true for a person to inhale?
stimulate the intercostal and phrenic nerves. Intercostal nerves a. Intrapulmonary pressure is greater than atmospheric pressure.
cause the external intercostal muscles to contract. The phrenic
b. Atmospheric pressure is greater than intrapulmonary pressure.
nerve stimulates the diaphragm. Expiration occurs rhythmically
when respiratory control areas stop nervous stimulation and c. The abdominal muscles must contract.
allow the muscles to relax. d. a and c
6. Suppose you’re a respiratory therapist and you want to mea-
sure your patient’s tidal volume, inspiratory reserve volume,
and expiratory reserve volume. What would you tell him or her
Nervous Input
to do during the test? Describe the steps you’d use.
By observing our breathing during day-to-day living, it’s evi-
Answers in Appendix A.
dent that higher brain centers influence the rate and depth of
respiration. Input from the cerebral cortex, limbic system,
hypothalamus, and other brain centers causes increased respi-
ration rate and depth if you’re angry, frightened, or otherwise 14.3 Gas Exchange and Transport
upset. Faster-than-normal respiration is referred to as hyperpnea. 7. Describe the process of gas exchange in the lungs and the tissues.
Conversely, respiration rate and depth decrease in the soundest 8. Explain how oxygen and carbon dioxide are transported in
stages of sleep. Conscious control of respiration allows a person the blood.
to hold his breath for a time, or to voluntarily hyperventilate.
Neural influence over the respiratory centers also helps increase Respiration includes exchange of gases both in the lungs and in the
respiratory rate and depth during exercise. tissues. Both are critical to homeostasis. Recall that diffusion is
Nervous control over respiration also helps to protect delicate the movement of molecules from a higher concentration to a lower
lung tissue, as illustrated by the Hering-Breuer reflex. During ex- concentration. The principles of diffusion alone govern whether
ercise, inspiratory depth increases, due to recruitment of muscle oxygen (O2) or carbon dioxide (CO2) enters or leaves the blood in
fibers in the diaphragm, intercostal muscles, and accessory mus- the lungs and in the tissues.
cles. Then, stretch receptors in the bronchi, bronchioles, and the
walls between adjacent alveoli are stimulated; in turn, they pro-
duce inhibitory nerve signals that travel from the inflated lungs External Respiration
to the respiratory center. This causes the respiratory center to stop External respiration is the exchange of gases in the lungs. Specifi-
sending out nerve signals. This reflex helps support rhythmic cally, during external respiration, gases are exchanged between the
respiratory movements by limiting inspiration, thus preventing alveolar air and the pulmonary capillary blood. Blood that enters the
overexpansion of lung tissue. pulmonary capillaries is dark maroon because it is relatively O2-poor.
external respiration
alveolar air
body during expiration. O2
Another way to explain gas exchange in the lungs is to con- CO2
sider the partial pressure of the gases involved. As the molecules
of gases move randomly in all directions, they exert pressure. As
O2
an analogy, imagine blowing up a balloon, then holding its neck
closed. When you open the balloon, air escapes—it rushes out from
high pressure (inside) to low pressure (outside). In the alveoli, the CO2
amount of pressure each gas exerts is its partial pressure, symbol-
ized as Po2 and Pco2. Alveolar air has a much higher Po2 than does pulmonary
blood; thus, oxygen rushes into the blood. The pressure pattern is circulation
the reverse for CO2: blood in the pulmonary capillaries has a higher
Pco2 than the air in the alveoli. Carbon dioxide escapes pulmonary
blood to enter the alveoli. O2-poor blood
O2-rich blood
CO2
O2 O2
gas transport
Internal Respiration CO2
O2
CO2 diffuses from the tissue fluid into the blood. Figure 14.10
summarizes our discussion of gas exchange in the lungs and tis-
tissue fluid
sues and shows the differences in O2 and CO2 that lead to diffusion
of these gases. CO2 CO2
O2
Again, we can explain exchange in the tissues by consider-
ing the partial pressure of the gases involved. In this case, oxygen
diffuses out of the blood into the tissues because the Po2 in tissue respiring tissues
fluid is lower than that of the blood. Carbon dioxide diffuses into
Figure 14.10 External and internal respiration. During exter-
the blood from the tissues because the Pco2 in tissue fluid is higher nal respiration in the lungs, CO2 leaves the blood and O2 enters
than that of the blood. the blood passively by diffusion. During internal respiration in the
tissues, O2 leaves the blood and CO2 enters the blood passively
by diffusion.
Gas Transport
The mode of transport of oxygen and carbon dioxide in the blood
differs, although red blood cells are involved in transporting both the body’s oxygen at any given time because oxygen is not very
of these gases. soluble in water.
Hemoglobin is remarkably suited to the task of transport-
ing oxygen because it can either combine with or release oxygen
Oxygen Transport (depending upon its surroundings). The higher concentration of
After O2 enters the blood contained in pulmonary capillaries of the oxygen in the alveoli, plus the slightly higher pH and slightly cooler
lungs, it enters red blood cells and combines with the iron portion temperature, causes hemoglobin to take up oxygen and become
of hemoglobin, the pigment in red blood cells. In addition, a small oxyhemoglobin (HbO2). The lower concentration of oxygen in the
amount of oxygen is transported as a dissolved gas in the watery tissues, plus the slightly lower pH and slightly warmer temperature
blood plasma. This dissolved oxygen amounts to only 2–3% of in the tissues, causes hemoglobin to release oxygen and become
Pneumonia Bronchitis
Alveoli fill with pus and fluid, Airways are inflamed due
making gas exchange difficult. to infection (acute) or due to
an irritant (chronic). Coughing
brings up mucus and pus.
asbestos tubercle
body
Figure 14.11 Common bronchial and pulmonary diseases. Exposure to infectious pathogens and/or polluted air, including
tobacco smoke, causes the diseases and disorders shown here.
Poverty and HIV are the risk factors most closely associated with the toward deflation. Breathing asbestos is also associated with the
disease, and 95% of TB victims live in developing countries. Many development of cancer. Because asbestos was formerly used widely
of these people are infected with multiple-drug-resistant (MDR) as a fireproofing and insulating agent, unwarranted exposure has
tuberculosis, a form that is not easily controlled by the standard set occurred. It has been projected that more than 300,000 deaths
of antibiotics used to fight TB. However, there is good news for caused by asbestos exposure—mostly in the workplace—will
the United States, where the incidence of both common and MDR occur in the United States between 2012 and 2020.
tuberculosis infection is in decline and hit a record low in 2013. Coal-dust pneumoconiosus is also known as black lung, and
Public health officials credit several interventions for this improve- it is found in miners who are not adequately protected against in-
ment: a very vigorous response to new infection, including physician haling coal dust. The dust collects in the bronchi, forming small
and patient education, more effective infection control, and close su- deposits called nodules. These nodules can harden and destroy the
pervision of patients in active treatment. The World Health Organiza- lung tissue that surrounds them, gradually decreasing the patient’s
tion is developing similar strategies for use in other countries. ability to inflate his lungs. Victims of black lung are also more
susceptible to tuberculosis and pneumonia. The symptoms of black
Restrictive Pulmonary Disorders lung can be treated with various medications, but the only cure for
the disorder is a lung transplant.
In restrictive pulmonary disorders, vital capacity is reduced because
the lungs have lost their elasticity. An entire class of restrictive
pulmonary disorders, called pneumoconioses, is caused by inhal- Obstructive Pulmonary Disorders
ing particles such as silica (sand), asbestos, clay, cement, flour, In obstructive pulmonary disorders, air does not flow freely in the
and fiberglass. Pneumoconioses can lead to pulmonary fibrosis, airways, and the time it takes to inhale or exhale maximally is
a condition in which fibrous connective tissue builds up in the greatly increased. Chronic bronchitis and emphysema are referred
lungs. The lungs cannot inflate properly and are always tending to as chronic obstructive pulmonary disorders (COPD) because
What are the chances of being cured of lung cancer? Does smoking cause any special health problems
Very low; the five-year survival rate is only 13%. However, it is for women?
important to remember that lung cancer, or bronchogenic carcinoma Yes. Women who smoke and use the birth control pill have an increased
in technical terms, is very rare (although not unheard of) in nonsmok- risk of stroke and blood clots in the legs. In addition, women who
ers. Thus, lung cancer is largely preventable: Don’t smoke, and avoid smoke increase their chances of getting cancer of the uterine cervix.
exposure to smoke.
What are some of the short-term effects
Does smoking cause other lung diseases? of smoking cigarettes?
Yes. Smoking leads to chronic bronchitis, a disease in which the air- Almost immediately, smoking can make it hard to breathe. Within a
ways produce excess mucus, forcing the smoker to cough frequently. short time, it can also worsen asthma and allergies. Only seven
Smoking is also the major cause of emphysema, a disease that slowly seconds after a smoker takes a puff, nicotine reaches the brain, where
destroys a person’s ability to breathe. Chronic bronchitis and pulmo- it produces a morphinelike effect.
nary emphysema rates are higher in smokers than in nonsmokers.
Are there any other risks to the smoker?
Why do smokers have “smoker’s cough”? Yes, there are many more risks. Smoking is a cause of stroke, which is
Remember the mucociliary escalator (page 322)? This is the protective the third leading cause of death in the United States. Smokers are more
mechanism for the lungs and the airways: a sheet of mucus present in likely to have and die from stomach ulcers than are nonsmokers. Smok-
the trachea, bronchi, and bronchioles. Normally, constantly beating ers have a higher incidence of cancer in general. If a person smokes and
cilia on the cells lining the airways move the sheet upward. Once at the is exposed to radon or asbestos, the risk for lung cancer increases dra-
pharynx, mucus can be swallowed or spit out. Smoking is a double matically. Research continues to show that smoking is also a major risk
assault on the mucociliary escalator: First, inhaled, nasty toxins and factor for autoimmune diseases as well. These include Crohn’s disease
particles cling to the sticky mucus. Then, a big dose of nicotine para- (which affects the digestive tract), psoriasis (which affects skin and
lyzes the cilia for 30 minutes or more. Long-term smokers will elimi- connective tissue), and Buerger’s disease (which causes inflammation
nate the delicate, ciliated epithelial cells entirely, replacing them with and destruction of blood vessels, especially in the limbs).
a sturdier epithelium better able to stand the heat of cigarette smoke.
The result: There is no way to clear accumulated mucus (and the What are the dangers of passive smoking?
trapped contaminants in it) except to cough it out. The longer a person Passive smoking causes lung cancer in healthy nonsmokers. Children
smokes, the more pronounced and productive the cough becomes. whose parents smoke are more likely to suffer from pneumonia or
bronchitis in the first two years of life than are children who come
If you smoke but don’t inhale, is there any danger? from smoke-free households, and children of smokers are more likely
Yes. Wherever smoke touches living cells, it does harm. So, even if to develop asthma during childhood. Passive smokers have a 30%
smokers of pipes, cigarettes, and cigars don’t inhale, they are at an greater risk of developing lung cancer than do nonsmokers who live
increased risk for lip, mouth, and tongue cancer. in a smoke-free house.
—Continued
Are chewing tobacco and snuff safe alternatives to determined that to be successful, a smoker should use the
cigarette smoking? START plan:
No, they are not. Many people who use chewing tobacco or snuff 1. Set a date, and get ready to quit: Think of all of the reasons you
believe it can’t harm them because there is no smoke. Wrong. Smoke- want to quit, and write them down. (For starters, you’ll save
less tobacco still contains nicotine, the same addicting drug found in money and you’ll feel better!) Once you’ve decided on a date,
cigarettes and cigars. Although not inhaled through the lungs, the juice plan ahead. Review what worked, or didn’t, in the past.
from smokeless tobacco is absorbed through the lining of the mouth. 2. Tell others: Inform your family, friends, and co-workers of your
There it can cause sores and white patches, which often lead to cancer intention to quit, and ask them not to smoke around you. Once
of the mouth. Snuff dippers actually take in an average of over ten you quit, don’t take another puff from a cigarette.
times more cancer-causing substances than cigarette smokers. 3. Anticipate the problems you might encounter. Learn new
behaviors that aren’t associated with smoking: When you first
But what about those e-cigarettes? Those seem like
quit, change your routine completely so that subconscious
they ought to be pretty safe to use.
cues to smoke don’t keep appearing. Take a different route to
Electronic cigarettes, or e-cigarettes, vary in their style, but all basically work, eat breakfast in a different place, drink tea instead of
consist of a cartridge containing a nicotine solution, a heat source that heats coffee. When the urge to smoke recurs, distract yourself with
the solution into a vapor, and a battery to power the heat source. The user physical or mental activity. Exercise or talk to someone to
inhales the addictive nicotine vapor, along with whatever other additives are reduce stress. Each day, plan something fun and pleasurable
in the liquid. Over 700 different flavors—including soda, candy, fruit, and for yourself.
alcohol flavors—can be added to make the solution more attractive to the 4. Remove anything related to smoking from your home and
smoker. In addition, propylene glycol and glycerol are two ingredients that workplace. Throw out all smoking materials: cigarettes, pipes,
are added to dissolve the nicotine and keep it soluble. However, when ashtrays, lighters, etc. Avoid spending time with people who
exposed to the high heat necessary to vaporize e-cigarette liquid, these com- might undermine your efforts, especially other smokers!
pounds break down to form carcinogens. Propylene glycol and glycerol 5. Talk to your health-care provider to get support,
form formaldehyde and acetaldehyde, both of which are carcinogenic, and encouragement, and help to quit. Never be embarrassed to ask
flavorings can also create cancer-causing agents when burned. Further- for, and use, antismoking medication. Nicotine comes in gum
more, e-cigarettes contain many of the same contaminants as their tradi- and patches (both sold over the counter) and in prescription
tional counterparts: heavy metals (including toxic lead), organic inhaler and nasal spray forms. Using these products can help you
carbon–containing compounds, small particles, and ash. The bottom line is to overcome the cravings for nicotine that occur immediately
that they are clearly toxic, and are likely no safer than traditional cigarettes. after quitting. In addition, use of antidepressants (available by
One thing is certain: public health officials are increasingly view- prescription) has been shown to significantly increase a patient’s
ing e-cigarettes as a societal menace, especially for children and youth. chances of quitting for good. Chantix®, an antidepressant, also
Babies and children have been accidently poisoned from drinking the reduces the effects of nicotine addiction by blocking nicotine
nicotine-laced solution, and burned by the hot cartridge. The vapor fla- receptors. Private and group smoking cessation counseling often
vorings are tailored to appeal to young people, with flavors such as helps, and is available for free or at a low cost. Your local health
bubble gum, cherry, and grape. Studies show that adolescents and teens department will have information about programs in your area.
who use e-cigarettes are more than twice as likely as their peers to transi- There are even apps for your mobile device to help support your
tion to traditional cigarettes. While over 40 states prohibit direct sales to efforts to quit, and you can sign up for a text service that will
minors, e-cigarettes are easily purchased over the Internet, and there is send you regular text messages with tips, advice, and encourage-
no minimum age for those types of purchases. Moreover, if you’re trying ment while you quit.
to quit smoking, you need to be aware that e-cigarettes have not been
approved by the Food and Drug Administration for smoking cessation. And remember—if at first you don’t succeed, try, try again!
In fact, physicians are concerned that smokers may try to use them to The first three to six months after quitting will be the toughest, and
quit, instead of traditional, FDA-approved medications. So think again if that’s when many people go back to smoking. Don’t be discouraged if
you have been considering e-cigarettes to be a safe, appealing, and fun this happens to you. On average, most people try to quit at least twice
alternative to cigarettes, cigars, pipes, and chewing tobacco. before finally succeeding. To avoid a relapse, don’t drink alcohol and/
or hang around with other smokers. Studies have shown that both can
Okay, okay, enough already! You’ve convinced me lead to failure in the attempt to quit. Weight gain and increased irrita-
that I should quit. But how? I’ve tried before. Is there bility or depression can also be expected. Exercise and eating a
a better way to quit smoking? healthy diet will minimize both of these side effects.
The U.S. Office of the Surgeon General has done extensive research For more information, visit the Surgeon General’s stop-smoking
on the most effective ways to quit smoking. This research has website: http://smokefree.gov.
tumor
Figure 14.12 Normal lung versus diseased lungs. (a) Normal lung. Note the healthy red color. (b) Lung of an emphysema victim.
Small black deposits from smoking can be seen throughout. The apex (upper portion) of the lung shows lung tissue that has broken
down. (c) Lung from a heavy smoker. Notice how black the lungs are except where the large red cancerous tumor has formed.
It’s difficult for most of us to imagine a world where a whiff of A new treatment called a bronchial thermoplasty is now avail-
perfume or disinfectant, a faceful of smoke from a careless able for individuals with bronchial smooth muscle thickening, whose
smoker, a bout of strenuous exercise or even someone’s cat could asthma cannot be controlled by medication alone. Using this tech-
disrupt our breathing to the point where we would need nique, the pulmonologist (a physician who specializes in lung disor-
hospitalization—and even worse, knowing that any one of those ders) passes a long, slender tube called a bronchoscope through the
things could kill us. Yet that’s the world in which people with nasopharynx and trachea. The bronchoscope is then advanced as far
asthma live. As you know, asthma is caused by bronchi whose as possible into a section of the patient’s bronchi (see Figure 14.1).
smooth muscle is over-reactive. In response to any of the triggers There, electrodes on the tip of the bronchoscope are heated with
just mentioned, the muscle goes into spasm, reducing airway size radiofrequency energy, causing the surrounding muscle to shrink and
and causing the characteristic asthma symptoms: coughing, thereby increasing the diameter of the bronchus. Patients must
wheezing, a breathless sensation. People with chronic asthma undergo three or more treatment sessions under mild sedation because
actually develop a thickening in the bronchial smooth muscle, a different section of the lung is treated with each session. The therapy
which increases the severity of their disease. The two preferred has been proven to be very effective for individuals with chronic
categories of drugs used to control asthma are inhaled bronchodi- asthma.
lators and steroids, but they are not consistently effective for For more information about asthma and asthma treatment, visit
people with chronic asthma. the Asthma and Allergy Foundation of America at http://aafa.org.
cutting off the supply of air to that lung. The entire lung then col- 14.5 Effects of Aging
lapses, the secretions trapped in the lung spaces become infected,
11. Describe the anatomical and physiological changes that occur
and pneumonia or a lung abscess (localized area of pus) results. in the respiratory system as we age.
The only treatment that offers a possibility of cure is to remove
a lobe or the entire lung before metastasis has had time to occur.
This operation is called pneumonectomy. If the cancer has spread, Respiratory fitness decreases with age. Maximum breathing
chemotherapy and radiation are also required. capacities decline, while the likelihood of fatigue increases.
The Medical Focus on pages 333–334 lists the various illnesses, Inspiration and expiration are not as effective in older persons.
including cancer, that are apt to occur in persons who smoke. Cur- With age, weakened intercostal muscles and decreased
rent research indicates that passive smoking—exposure to smoke elasticity of the rib cage combine to reduce the inspiratory
created by others who are smoking—can also cause lung cancer and reserve volume, while the lungs’ inability to recoil reduces the
other illnesses associated with smoking. If a person stops voluntary expiratory reserve volume. As a result, more residual air is
smoking and avoids passive smoking, and if the body tissues are not found in the lungs of older people, and the residual volume
already cancerous, they may return to normal over time. increases.
With age, gas exchange in the lungs becomes less efficient,
Content CHECK-UP! not only due to changes in the lungs but also due to changes in
the blood capillaries. The respiratory membrane thickens, and the
10. What type of lower respiratory infection should be treated with
antibiotics? What kind should never be treated using gases cannot diffuse as rapidly as they once did.
antibiotics, and why? Respiratory diseases, such as those discussed in
11. Obstructive pulmonary diseases include: section 14.4, are more prevalent in older people than in the
general public. In the elderly, the ciliated cells of the trachea
a. emphysema. c. asthma.
are reduced in number, and those remaining are not as effective
b. chronic bronchitis. d. All of the above.
as they once were. As you know from Chapter 13, other aspects
12. Which of the following increases in a person with emphysema?
of the immune response also diminish in the elderly, including
a. amount of surface area in the lung for gas exchange the numbers and effectiveness of the white blood cells. Thus,
b. residual volume pneumonia and other respiratory infections are among the lead-
c. amount of elastic tissue in the lungs ing causes of death in older persons. For this reason, the Cen-
d. amount of oxygen delivered to the brain and heart ters for Disease Control (CDC) recommends that everyone who
Answers in Appendix A. is older than 65 receive the pneumococcal vaccine to prevent
pneumonia.
Content CHECK-UP!
This reaction lowers blood pH because free H (hydrogen 1
14. Lung disease often _____ carbon dioxide levels in the blood,
ions) are formed during the reaction as carbonic acid dissociates. causing _____.
The greater the amount of CO2 in the blood, the greater the car- a. increases; acidosis
bonic acid formed, and the more free hydrogen ions are formed. b. increases; alkalosis
Conversely, when carbon dioxide starts to diffuse out of the blood
c. decreases; acidosis
in the lungs, the reaction occurs in the reverse direction. Carbon
dioxide concentration in blood decreases (because it is being ex- d. decreases; alkalosis
haled), and carbonic acid concentration decreases, too. Now, the Answer in Appendix A.
blood pH rises.
Summary
14.1 The Respiratory System C. The larynx is the voice box. It then into bronchioles. The lungs
The four main actions of the respira- houses the vocal cords. The are composed of bronchi, bron-
tory system are (1) ventilation, (2) ex- glottis, a slit between the vocal chioles, alveoli, pulmonary capil-
ternal respiration (gas exchange in cords, is covered by the epiglot- laries, and connective tissue.
the lungs), (3) internal respiration (gas tis when food is being swal- E. The respiratory membrane is
exchange in the tissues), and (4) the lowed. formed by the alveolar wall and
transport of gases in the blood. D. The trachea and the primary capillary wall, joined by base-
A. The nasal cavities, which filter, bronchi are held open by carti- ment membrane. The large sur-
warm, and humidify incoming air, laginous rings. The trachea di- face area and thinness of the
open into the pharynx. vides to form two primary respiratory membrane allow
B. The food and air passages cross bronchi, one to supply each lung. rapid gas exchange.
in the pharynx, which conducts The cartilage rings gradually dis- 14.2 Mechanism of Breathing
air to the larynx and food to the appear as the primary bronchi A. Ventilation is the movement of
esophagus. branch into smaller bronchi and gases into and out of the lungs.
Learning Outcomes After you have studied this chapter, you should be able to:
15.1 Anatomy of the Digestive 15.3 Chemical Digestion 12. Describe the functions of the major
vitamins and minerals in the body.
System 7. Name and state the functions of the
1. Trace the path of food through the digestive enzymes for
alimentary canal, and describe the carbohydrates, proteins, and fats. Focus on Forensics
general structure and function of The Stories That Teeth Can Tell
each organ mentioned. 15.4 Effects of Aging
2. Describe the wall of the small 8. Describe the anatomical and Medical Focus
intestine, and relate its anatomy to physiological changes that occur in Disorders of the Digestive Tract
nutrient absorption. the digestive system as we age.
3. Describe peristalsis, and state its Human Systems Work Together
function. 15.5 Homeostasis
Digestive System
4. Name the hormones produced by 9. Explain how the digestive system
the alimentary canal that help control works with other systems of the
digestive secretions. body to maintain homeostasis.
Medical Focus
Tips for Effectively Using Nutrition
15.2 Accessory Organs of Digestion 15.6 Nutrition Labels
5. Name five accessory organs of 10. State the functions of glucose, fats,
digestion. and amino acids in the body. Medical Focus
6. Outline the location, anatomy, and 11. Define the terms essential fatty acid, Bariatric Surgery for Obesity
functions of the pancreas, the liver, essential amino acid, and vitamin.
and the gallbladder.
342
Accessory organs
parotid
Salivary glands
secrete saliva and sublingual
digestive enzyme Mouth
submandibular teeth chew food; tongue tastes and
pushes food for chewing and swallowing
Pharynx
passageway where food is swallowed
Esophagus
passageway where peristalsis pushes
food to stomach
diaphragm
Liver
major metabolic organ: Stomach
processes and stores nutrients; secretes acid and digestive enzyme
produces bile for emulsification of fats for protein; churns, mixing food with
secretions, and sends chyme to
Gallbladder small intestine
stores bile from liver; sends it to
small intestine
Small intestine
Pancreas mixes chyme with digestive enzymes
produces pancreatic juice, which contains for final breakdown; absorbs nutrient
digestive enzymes; sends it to the small molecules into body; secretes
intestine; produces insulin and secretes digestive hormones into blood
it into blood after eating
Large intestine
absorbs water and salt to form feces
Anus
enamel
crown dentin
pulp
hard palate gum
jawbone
soft palate
periodontal
molars (3) membrane
premolars (2)
cementum
canine (1)
incisors (2)
a. b.
Figure 15.2 Human teeth. (a) The chisel-shaped incisors bite; the pointed canines tear; the fairly flat premolars grind;
and the flattened molars crush food. The last molar, called a wisdom tooth, may fail to erupt, or if it does, it is sometimes crooked
and useless. Often dentists recommend the extraction of the wisdom teeth. (b) Longitudinal section of a tooth. The crown is the por-
tion that projects above the gumline and can be replaced by a dentist if damaged. When the periodontal membrane is inflamed, the
tooth can loosen.
to the ears between the cheek and the masseter muscle. They have the lower jaw. The ducts from the sublingual and submandibular
ducts that open on the inner surface of the cheek at the location of glands open under the tongue. You can locate the openings for the
the second upper molar. The parotid glands swell when a person salivary glands if you use your tongue to feel for small flaps on the
has the mumps, a disease caused by a viral infection. The sublin- inside of your cheek and under your tongue. Saliva is a solution
gual glands are located beneath the tongue, and the submandibu- of mucus and water. It also contains bicarbonate and an enzyme
lar glands are in the floor of the mouth on the inside surface of called salivary amylase, which begins the process of digesting
peristaltic
soft wave
bolus
palate
epiglottis
esophagus
glottis is closed
larynx rises and lower gastroesophageal
trachea epiglottis covers esophagus sphincter relaxes and
(airway) open glottis stomach
esophagus food enters stomach
opens
a. Swallowing b. Peristalsis
Figure 15.3 Swallowing. (a) When food is swallowed, the soft palate closes off the nasopharynx, and the epiglottis covers the glottis,
forcing the bolus to pass down the esophagus. Therefore, a person does not breathe while swallowing. (b) Peristalsis moves food
through the gastroesophageal sphincter into the stomach.
submucosa mucosa
submucosa
lumen lumen
artery muscularis
serosa vein
muscularis
adventitia
a. b.
Figure 15.4 Wall of the alimentary canal. (a) Several different types of tissues are found in the wall of the alimentary canal.
Note the placement of circular muscle inside longitudinal muscle. (b) Micrograph of the wall of the esophagus.
Serosa (serous membrane layer) Most of the alimentary canal has mouth to the stomach. The entrance of the esophagus to the
a serosa, a very thin, outermost layer of squamous epithelium stomach is marked by a constriction, often called the esophageal
supported by connective tissue. The serosa secretes a serous sphincter. It’s important to note that the esophageal sphincter
fluid that keeps the outer surface of the intestines moist so isn’t a true sphincter muscle. A true sphincter muscle (such as
that the organs of the abdominal cavity slide against one an- the pyloric sphincter, discussed with the stomach) is an actual
other. The esophagus has an outer layer composed only of ring of muscle that closes a tube when it contracts and opens the
loose connective tissue called the adventitia. tube when it relaxes. Although not an actual ring of muscle, the
esophageal sphincter functions as one because it allows the bolus
Although the gut is a continuous tube, its different regions
to pass into the stomach when relaxed (see Fig. 15.3). Likewise,
have individual characteristics uniquely suited to each region’s par-
the sphincter prevents the stomach’s acidic contents from backing
ticular function. For example, the stomach’s circular, longitudinal
up into the esophagus when contracted. When vomiting occurs,
and oblique muscle layers enable it to mix food. You’ll read about
contraction of the diaphragm and abdominal muscles propels the
other specializations as you continue through this chapter.
stomach’s contents past the esophageal sphincter upward through
the esophagus.
The Esophagus
The esophagus is a muscular tube that lies posterior to the tra- The Stomach
chea. It passes from the pharynx through the thoracic cavity and
The stomach (Fig. 15.5) is a thick-walled, J-shaped organ that
diaphragm into the abdominal cavity, where it joins the stomach.
lies on the left side of the abdominal cavity inferior to the dia-
The esophagus is ordinarily collapsed, but it opens and receives the
phragm and posterior to the liver. The stomach is continuous with
bolus when swallowing occurs.
the esophagus superiorly and the duodenum of the small intestine
A rhythmic contraction called peristalsis pushes the food
inferiorly.
along the alimentary canal. In peristalsis, short segments of
The length of the stomach remains at about 25 cm (10 in.)
smooth muscle built into the wall of the digestive tract alternately
regardless of the amount of food it holds, but the diameter varies,
contract and then relax. Peristalsis constantly moves food forward
depending on how full it is. As the stomach expands, deep folds in
through the digestive tract. (As an analogy, think of squeezing a
its wall, called rugae, stretch out and gradually disappear. When
toothpaste tube, starting at the bottom, then continuing upward
full, the stomach can hold about 4 liters (1 gallon). The stomach
along the entire length of the tube. If you do it correctly, the
receives food from the esophagus, stores food, liquifies food by
toothpaste moves forward until the tube is empty.) Peristalsis
mixing food with its juices (thereby starting the digestion of pro-
begins in the esophagus and continues in all the organs of the
teins), and moves food into the small intestine.
alimentary canal. Occasionally, peristalsis begins even though
there is no food in the esophagus. This produces the sensation of
a lump in the throat. Regions of the Stomach
The esophagus plays no role in the chemical digestion of The stomach has four regions. The cardiac region, which is near
food. Its sole purpose is to transport the food bolus from the the heart, surrounds the lower esophageal sphincter where food
gastric gland
a.
duodenum parietal
cells
gastric pit
gastric gland
chief cells
b. c. 20 µm
Figure 15.5 Anatomy and histology of the stomach. (a) The stomach has a thick wall with deep folds, rugae, that allow it to
expand and fill with food. (b) The stomach lining has gastric glands, which secrete mucus and protein-digesting gastric juice. (c) Photomi-
crograph of the stomach lining.
enters the stomach. The fundic region, which holds food tempo- pepsin when exposed to hydrochloric acid. Parietal cells produce
rarily, is an expanded portion superior to the cardiac region. The the hydrochloric acid. The HCl causes the gastric juice in the stom-
body region, which comes next, is the main part. The pyloric ach to have a high acidity with a pH of about 2; this is beneficial
region narrows to become the pyloric canal leading to the pyloric because it kills most of the bacteria present in food. Although HCl
sphincter. Food passes through this sphincter and enters the duo- does not digest food, it does break down the connective tissue of
denum, the first part of the small intestine. meat and activates pepsin.
Parietal cells also produce intrinsic factor, a glycoprotein
that binds to vitamin B12, preventing this vitamin from being
Digestive Functions of the Stomach destroyed in the harsh, acidic environment of the stomach. If
The stomach acts on food both chemically and physically. Its wall the stomach fails to produce intrinsic factor, or if the diet is
contains three muscle layers: One layer is longitudinal, another is deficient in vitamin B12, a serious disorder called pernicious
circular, and the third is obliquely arranged. This muscular wall not anemia will result. Lacking the vitamin, red blood cells will
only moves the food along, but it also churns, mixing the food with fail to develop.
gastric juice and breaking it down to small pieces. Enteroendocrine cells of the gastric glands produce the hor-
The term gastric always refers to the stomach. The columnar mone gastrin. This hormone enters stomach blood vessels and
epithelial lining of the stomach has millions of gastric pits, which is circulated throughout the stomach. Gastrin regulates muscular
lead into gastric glands (Fig. 15.5a, b). Gastric glands contain contraction and secretion by the stomach. Histamine from ECL
four types of secretory cells: chief cells, parietal cells, enteroendo- cells prolongs the effect of gastrin, causing additional acid to be
crine cells, and mucous cells. Other secretory cells found scattered secreted. However, it’s important to be able to inhibit acid secretion
throughout the glands are ECL cells and D cells. The gastric glands when appropriate, and that is the role of the somatostatin secreted
produce gastric juice, a watery solution that contains pepsinogen, by the D cells.
hydrochloric acid (HCl), intrinsic factor, and mucus. Chief cells The wall of the stomach is protected by the thick layer of
secrete pepsinogen, which becomes the protein-digesting enzyme mucus secreted by the mucous cells. If, by chance, HCl penetrates
lumen lacteal
blood
capillaries
lymph
nodule
venule
lymphatic
a. vessel b.
arteriole
Figure 15.7 Anatomy of the small intestine. (a) The wall of the small intestine has folds that bear fingerlike projections
called villi (sing., villus). (b) Photomicrograph of intestinal villi. Villi in turn have projections called microvilli. (c) Photomicrograph of
a villus with its microvilli. The products of digestion are absorbed by microvilli and enter the blood capillaries and the lacteals of
the villi.
carbohydrates) and amino acids (digested from protein) enter the Enteroendocrine hormones produced by cells in the stomach and
blood capillaries of a villus. Glycerol and fatty acids (digested small intestine participate as well.
from fats) enter the epithelial cells of the villi, and within these Three phases occur as the control mechanisms become ac-
cells are joined and packaged as lipoprotein droplets, which enter tive. The first, the cephalic phase (remember from Chapter 1 that
a lacteal. Thus, lipids first enter the lymphatic capillaries and are cephalic means “head”), begins when we look at, think about,
ultimately transported in the lymph to the lymphatic ducts. Recall smell, or taste food. Sensory signals are relayed to the hypothala-
that the lymphatic ducts return lymph to the bloodstream by way mus, the brain center that stimulates hunger. In turn, the hypothal-
of the subclavian veins (p. 294). After nutrients are absorbed into amus triggers autonomic nerves belonging to the parasympathetic
the blood, they are eventually carried to all the cells of the body by nervous system to automatically stimulate secretion and muscle
the bloodstream. contraction. Filling the stomach helps to trigger the next regula-
As we noted previously, a third function of the small intestine tory mechanism: the gastric phase of control. The presence of
is movement of nondigested remains to the large intestine. The food (particularly food high in amino acids) that stretches the
wall of the small intestine has two types of movements: segmenta- stomach causes stimulation of the enteric nerve network. At the
tion and peristalsis. Segmentation refers to localized contractions same time, the stomach hormone gastrin is also released. Gastrin
and constrictions that mix the chyme thoroughly with digestive is transported in the bloodstream to nearby smooth muscle and
juices. Segmentation also encourages absorption of nutrients into gastric glands. Gastric contraction and secretion by gastric glands
the bloodstream or lymph. Peristalsis then moves nondigested re- are controlled internally by cooperation of these two mechanisms.
mains toward the large intestine. Both muscle contraction and gastric gland secretion increase in
response.
A similar nerve network and hormone set cooperate with
Regulation of Contraction and Secretion in the
parasympathetic nerve activity to trigger the third, or intestinal
Digestive Tract phase of secretion. When the duodenum is stretched by digested
A combination of three control mechanisms cooperates to regu- food that is rich in fatty acids and carbohydrate, the enteric
late the muscular contractions needed to move food throughout nervous system responds to stimulate intestinal secretion and
the gut, as well as the secretion of digestive juices needed for contraction. Simultaneously, cells of the duodenal wall produce
breaking down the food as it travels along. The central nervous three hormones that are of particular interest: secretin, gastric
system allows us to respond to hunger signals (and for many of inhibitory polypeptide (GIP; sometimes referred to as glucose-
us, stimulating eating behavior when we’re stressed). The enteric dependent insulinotropic polypeptide), and cholecystokinin
nervous system is a nerve network built directly into the wall of (CCK). Acid, especially hydrochloric acid (HCl) present in
the gut, allowing it to control its own movements and secretion. chyme, is a potent stimulator for secretin release, whereas
ascending descending
colon colon
goblet
cells
cecum
vermiform sigmoid
appendix colon
rectum
anal canal
haustrum
taenia coli
ileocecal
valve rectum
cecum
ileum
vermiform appendix
anal canal
rectum
veins
internal
anal sphincter
Figure 15.9 The large intestine. (a) The colon has four regions: the ascending colon, the transverse colon, the
descending colon, and the sigmoid colon. (b) Haustra (sing., haustrum) expand the colon’s volume, and taenia coli help to create
peristalsis so that defecation occurs. (c) The rectum and anal canal are at the distal end of the alimentary canal. (d) The intestinal
mucosa has many goblet cells.
urge is felt. The involuntary defecation reflex contracts the rectal Peritoneum
muscle and relaxes the internal anal sphincter, a ring of muscle that The abdominal wall and the organs of the abdomen are covered by
closes off the rectum. Then, feces move toward the anus. A pushing peritoneum, a serous membrane (Fig. 15.10). The portion of the
motion, along with the relaxation of the external anal sphincter, peritoneum that lines the wall is called the parietal peritoneum.
propels feces from the body. Because these activities are under The portion that covers the organs is called the visceral perito-
voluntary control, it is possible to control defecation. Defecation neum. In between the organs, the visceral peritoneum is a double-
normally occurs from three times a week to three times daily, and layered mesentery that supports the visceral organs, including the
some variation is normal. blood vessels, nerves, and lymphatic vessels.
mesocolon
c. mucosa, submucosa, muscularis, serosa.
duodenum
d. submucosa, mucosa, muscularis, serosa.
transverse colon
small 2. Which hormone is produced by the stomach and controls
intestine
greater omentum stomach contraction and secretion?
parietal peritoneum a. pepsin
b. gastrin
mesentery
c. cholecystokinin (CCK)
visceral peritoneum d. secretin
3. Unlike the other nutrients, lipids are not absorbed directly into
the bloodstream. Instead, they pass into lymphatic lacteals.
Why do you think they are absorbed this way? How do lipids
eventually make their way to the bloodstream?
ileum peritoneal cavity Answers in Appendix A.
rectum urinary bladder
bile
cystic duct
pancreatic
juice
gallbladder
duodenum
pancreatic islet
capillary
endocrine hormone-secreting
cells islet cells
Figure 15.11 The pancreas. (a) The pancreas is an exocrine gland when it secretes digestive enzymes into tubes that join to be-
come the pancreatic duct. The pancreatic duct and the common bile duct empty into the duodenum of the small intestine. (b) Pancreatic
exocrine and endocrine cells. Pancreatic juice produced by the exocrine cells contains enzymes that digest all types of food: carbohy-
drates, fats, proteins, and nucleic acids. Pancreatic endocrine cells secrete hormones.
hepatic
right lobe
portal vein
falciform
ligament inferior
vena cava left lobe
liver round ligament
of liver
gallbladder
Posterior
a.
hepatic cells
bile canals
hepatic
sinusoid
branch of
hepatic
central artery
vein
portal
bile
triad
duct
Figure 15.12 Macroscopic and
microscopic anatomy of the liver. (a) The liver
has two lobes viewed anteriorly (left) and
posteriorly from the visceral surface (right). branch of
(b) Cross section of a hepatic lobule, illustrating hepatic
microscopic structure. b. portal vein
blood from the stomach, pancreas, spleen, and intestines. The bile stored by the liver as glycogen. Between meals, glycogen is broken
ducts merge to form the common hepatic duct. down to glucose, which enters the hepatic veins. In this way, the
The central veins from each of the lobules enter a hepatic vein. blood glucose level remains within a homeostatic range.
With the help of Figure 12.18, trace the path of blood from the If the supply of glycogen is depleted, the liver converts glyc-
intestines to the liver via the hepatic portal vein and from the liver erol (from fats) and amino acids to glucose molecules. This pro-
to the inferior vena cava via the hepatic veins. cess is called gluconeogenesis. To convert amino acids to glycerol
for gluconeogenesis, the liver must first carry out deamination, a
Liver Functions complex metabolic pathway. Through this process, amino groups
are removed, converted to ammonia, and combined with carbon
As the blood from the hepatic portal vein passes through the liver, dioxide to form urea:
hepatic cells remove poisonous substances and detoxify them. The
liver also removes and stores nutrients and works to keep the con-
O
tents of the blood constant. It removes and stores iron and the fat-
soluble vitamins A, D, E, and K; makes the plasma proteins from 2 NH3 + CO2 H2N C NH2
amino acids; and helps regulate the quantity of cholesterol in the ammonia carbon dioxide urea
blood.
The liver maintains the blood glucose level at about 100 mg/ Urea is the usual nitrogenous waste product from amino acid
100 ml (0.1%), even though a person eats intermittently. When breakdown by the liver. Urea is normally excreted by the kidneys.
insulin is present, any excess glucose in the blood is removed and However, if it accumulates excessively, it can be toxic to the body.
Human beings are true omnivores when it comes to the foods we between this bacterium and ulcers, proved his theory to his skepti-
consume. When you consider the myriad of things that people eat— cal peers by drinking a culture of H. pylori—and giving himself an
habanero hot peppers, raw fish, insect larvae, seaweed, bacon-topped inflamed stomach!) For this reason, ulcers are now treated with
greasy cheeseburgers, and all the rest—it’s remarkable to think that antibiotics as well as antacids. Ulcers can also result from taking
the digestive tract and its accessory organs are durable enough to certain medications, including anti-inflammatory drugs such as
handle it all. However, even this sturdy system has its limits. Here are aspirin and ibuprofen. Discontinuing the medication usually
a few of the more common digestive tract disorders. allows the ulcer to heal.
Disorders of the Liver, Gallbladder, and Pancreas Autoimmune Disorders of the Digestive Tract
Hepatitis is inflammation of the liver, and it has many causes. As you know from Chapter 14, autoimmune diseases happen when
Viral hepatitis can be caused by one of five hepatitis viruses, but the body’s defense mechanisms launch an attack on cells, tissues,
the hepatitis A and B viruses are considered the most dangerous in and organs. Several autoimmune disorders affect the digestive
the United States. Hepatitis A is usually acquired from sewage- tract. Gluten-sensitive enteropathy, or celiac disease, is an allergic
contaminated drinking water. Hepatitis B is typically spread by hypersensitivity to the protein gluten, found in wheat, rye, and bar-
sexual contact, but it can also be spread by blood transfusions or ley. The allergy causes the small intestine lining to die off. If
contaminated needles. The hepatitis B virus is more contagious exposed to gluten in food or drink, the celiac disease sufferer expe-
than the AIDS virus, which is spread in the same way. The United riences painful cramping, diarrhea, and weight loss. He or she may
States Centers for Disease Control (CDC) recommends immuniza- also develop vitamin and mineral deficiencies. A strict gluten-free
tion for these viruses beginning in infancy (see Chapter 13, Medi- diet and nutritional supplements alleviate the symptoms of celiac
cal Focus: “Immunization: The Great Protector”). Both hepatitis C disease.
and D viruses are usually acquired by contact with infected blood. Inflammatory bowel diseases such as Crohn’s disease and
Hepatitis E has been found in sewage-contaminated water in sev- ulcerative colitis are autoimmune disorders characterized by
eral developing countries, including China, India, and Pakistan. severe diarrhea, cramping, fatigue, and weight loss. Ulcerative
Acute viral hepatitis can cause liver failure, and chronic viral hep- colitis is confined to the colon, but Crohn’s disease can be found
atitis B, C, and D can result in liver cancer. Cirrhosis is another anywhere along the entire length of the digestive tract, from the
chronic liver disease that often results from alcoholism. In alco- mouth to the anus. Both disorders can be effectively treated with a
holic cirrhosis, the organ becomes fatty, and liver tissue is replaced combination of steroids, chemotherapy drugs, and sometimes sur-
by inactive fibrous scar tissue. Hepatitis and cirrhosis affect the gery to remove damaged sections of the small intestine or colon.
entire liver, hinder its ability to repair itself, and are often fatal. Though there is no cure for these diseases, their symptoms may
Both cause jaundice, a yellowish tint to the skin and the whites of resolve over time. However, sufferers must learn to anticipate and
the eyes. Jaundice develops because the liver fails to properly control flare-ups.
lymphatic
blood capillary blood capillary
capillary
a. Carbohydrate digestion b. Protein digestion c. Fat digestion
Figure 15.13 Completing digestion and absorption in the small intestine. (a) Starch is digested to maltose by pancreatic amylase
and to glucose by the brush border enzyme maltase. Glucose is actively transported to intestinal villus cells and enters intestinal
capillaries. Disaccharides are similarly digested and absorbed. (b) Proteins are digested to amino acids by proteases and peptidases;
amino acids are actively absorbed by intestinal villus cells and enter the bloodstream. (c) Fats are emulsified by bile and digested to
monoglycerides and free fatty acids before diffusing into villus cells. In villus cells, they are reassembled into lipoproteins before diffusing
into lacteals.
bicarbonate (NaHCO3). One pancreatic enzyme, pancreatic amy- The peptidases are brush border enzymes that complete the
lase, digests starch (Fig. 15.13a): digestion of protein to amino acids. Peptides, which result from the
first step in protein digestion, are digested to amino acids by these
pancreatic
peptidases:
amylase
starch 1 H2O maltose peptidases
peptides 1 H2O amino acids
The three disaccharases (maltase, sucrase, and lactase) are
brush border enzymes produced by cells lining the small intestine. Like monosaccharides, amino acids are absorbed by intestinal
Intestinal disaccharases digest compound sugar molecules, called cells and enter intestinal capillaries.
disaccharides, into single sugar molecules, or monosaccharides. Lipase, a third pancreatic enzyme, digests fat molecules in the
Maltose, a disaccharide that results from the first step in starch fat droplets after they have been emulsified by bile salts (Fig. 15.13c):
digestion, is digested to glucose by maltase:
bile salts
maltase
fat fat droplets
maltose 1 H2O glucose 1 glucose
pancreatic lipase
Similarly, the enzyme sucrase digests table sugar (the disac- fat droplets 1 H2O glycerol and fatty acids
charide sucrose) and lactase digests milk sugar (the disaccharide
lactose). The monosaccharides that result are absorbed by intesti- As mentioned previously, glycerol and fatty acids enter the
nal cells and enter intestinal capillaries. cells of the intestinal villi. Within these cells, they are rejoined and
Recall that there are three pancreatic proteases, or enzymes packaged as lipoprotein droplets before entering the lacteals.
that digest protein: trypsin, chymotrypsin, and carboxypepti- Digestion of the nucleic acids DNA and RNA into free
dase. The following chemical equation summarizes their action nucleotides is accomplished by two pancreatic nuclease en-
(Fig. 15.13b): zymes. The free nucleotides can be further broken down into
their components by a phosphatase and a nucleosidase enzyme
pancreatic proteases built into the brush border cells. The phosphatase cleaves a
protein 1 H2O peptides and free amino acids phosphate from the nucleotide, leaving a molecule called a
Free amino acids are ready to be absorbed by the intestinal vil- nucleoside. The nucleosidase completes digestion into the nu-
lus cells. Peptides are too large and must undergo further digestion cleic acid’s three ingredient molecules: sugar, phosphate, and
in the small intestine. It is important to note that all three pancreatic organic base.
proteases are secreted in an inactive form and cannot digest protein Table 15.2 lists some of the major digestive enzymes produced
until they are inside the small intestine. This prevents them from by the gastrointestinal tract, salivary glands, or the pancreas. Each
accidentally digesting the pancreas itself. type of food is broken down by specific enzymes.
CARBOHYDRATE-DIGESTING ENZYMES
PROTEIN-DIGESTING ENZYMES
LIPID-DIGESTING ENZYMES
Pancreatic lipase Pancreas Small intestine Basic Fat droplet 1 H2O → glycerol 1 fatty acids
Content CHECK-UP!
11. Because the alimentary canal secretes gastrin and secretin, it
is considered a part of the _____ organ system.
Answer in Appendix A.
15.6 Nutrition
10. State the functions of glucose, fats, and amino acids in the body. Figure 15.14 Newest dietary guidelines, published by
11. Define the terms essential fatty acid, essential amino acid, the U.S. Department of Agriculture, and available at
and vitamin. www.choosemyplate.gov. The website can be customized for
12. Describe the functions of the major vitamins and minerals in the body. an individual’s age, gender, and activity level.
TABLE 15.3 Vitamins: Their Role in the Body and Food Sources
Vitamins Role in Body Good Food Sources
FAT-SOLUBLE VITAMINS
Vitamin A Assists in the formation and maintenance of Deep yellow/orange and dark green vegetables and fruits
healthy skin, hair, and mucous membranes; aids (carrots, broccoli, spinach, cantaloupe, sweet potatoes);
in the ability to see in dim light (night vision); is cheese, milk, and fortified margarine
essential for proper bone growth, tooth
development, and reproduction
Vitamin D Aids in the formation and maintenance of bones Milk fortified with vitamin D; tuna, salmon, or cod liver oil;
and teeth; assists in the absorption and use of also made in the skin when exposed to sunlight
calcium and phosphorus
Vitamin E Protects vitamin A and essential fatty acids from Vegetable oils and margarine; nuts; wheat germ and
oxidation; prevents plasma membrane damage whole-grain breads and cereals; green, leafy vegetables
Vitamin K Aids in synthesis of substances needed for clotting Green, leafy vegetables, cabbage, and cauliflower; also made
of blood; helps maintain normal bone metabolism by bacteria in intestines of humans, except for newborns
WATER-SOLUBLE VITAMINS
Vitamin C Is important in forming collagen, a protein that Citrus fruits, berries, melons, dark green vegetables,
gives structure to bones, cartilage, muscle, and tomatoes, green peppers, cabbage, potatoes
vascular tissue; helps maintain capillaries,
bones, and teeth; aids in absorption of iron;
helps protect other vitamins from oxidation
B-COMPLEX VITAMINS
Thiamin Helps in release of energy from carbohydrates; Whole-grain products, dried beans and peas, sunflower
promotes normal functioning of nervous system seeds, nuts
Riboflavin Helps body transform carbohydrates, proteins, and Nuts, yogurt, milk, whole-grain products, cheese, poultry,
fats into energy leafy green vegetables
Niacin Helps body transform carbohydrates, proteins, and Nuts, poultry, fish, whole-grain products, dried fruit, leafy
fats into energy greens, beans; can be formed in the body from
tryptophan, an essential amino acid found in protein
Vitamin B6 Aids in the use of fats and amino acids; aids in the Sunflower seeds, beans, poultry, nuts, bananas, dried fruit,
formation of protein leafy green vegetables
Folic acid Aids in the formation of hemoglobin in red blood Nuts, beans, whole-grain products, fruit juices, dark green
cells; aids in the formation of genetic material leafy vegetables
Pantothenic acid Aids in the formation of hormones and certain Nuts, beans, seeds, poultry, dried fruit, milk, dark green
nerve-regulating substances; helps in the leafy vegetables
metabolism of carbohydrates, proteins, and fats
Biotin Aids in the formation of fatty acids; helps in the Occurs widely in foods, especially eggs; made by bacteria
release of energy from carbohydrates in the human intestine
Vitamin B12 Aids in the formation of red blood cells and genetic Milk, yogurt, cheese, fish, poultry, eggs; not found in plant
material; helps in the functioning of the nervous foods unless fortified (as in some breakfast cereals)
system; requires intrinsic factor from the
stomach to be absorbed
Source: From David C. Nieman, et al., Nutrition, Revised 1st ed. Copyright © 1992 Wm. C. Brown Communications, Inc., Dubuque, Iowa.
TABLE 15.4 Minerals: Their Role in the Body and Food Sources
Minerals Role in Body Good Food Sources
MACRONUTRIENTS
Calcium Is used for building bones and teeth and for maintaining All dairy products; dark green, leafy vegetables; beans, nuts,
bone strength; also involved in muscle contraction, blood sunflower seeds, dried fruit, molasses, canned fish
clotting, and maintenance of plasma membranes
Phosphorus Is used to build bones and teeth; to release energy from Beans, sunflower seeds, milk, cheese, nuts, poultry, fish,
carbohydrates, proteins, and fats; and to form genetic lean meats
material, plasma membranes, and many enzymes
Magnesium Is used to build bones, to produce proteins, to release energy Sunflower and pumpkin seeds, nuts, whole-grain
from muscle carbohydrate stores (glycogen), and to products, beans, dark green vegetables, dried fruit,
regulate body temperature lean meats
Sodium Regulates body-fluid volume and blood acidity; aids in Most of the sodium in the U.S. diet is added to food as
transmission of nerve impulses salt (sodium chloride) in cooking, at the table, or in
commercial processing; animal products contain
some natural sodium
Chloride Is a component of gastric juice and aids in acid-base balance Table salt, seafood, milk, eggs, meats
Potassium Assists in muscle contraction, the maintenance of fluid and Widely distributed in foods, especially fruits and
electrolyte balance in the cells, and the transmission of vegetables, beans, nuts, seeds, and lean meats
nerve impulses; also aids in the release of energy from
carbohydrates, proteins, and fats
MICRONUTRIENTS (TRACE ELEMENTS)
Iron Is involved in the formation of hemoglobin in the red blood Molasses, seeds, whole-grain products, fortified
cells of the blood and myoglobin in muscles; also is a breakfast cereals, nuts, dried fruits, beans, poultry,
part of several enzymes and proteins fish, lean meats
Zinc Is involved in the formation of protein (growth of all tissues), Whole-grain products, seeds, nuts, poultry, fish, beans,
in wound healing, and in prevention of anemia; is a lean meats
component of many enzymes
Iodine Is an integral component of thyroid hormones Table salt (fortified), dairy products, shellfish, and fish
Fluoride Is involved in maintenance of bone and tooth structure Fluoridated drinking water is the best source; also found
in tea, fish, wheat germ, kale, cottage cheese,
soybeans, almonds, onions, milk
Copper Is vital to enzyme systems and in manufacturing red blood Nuts, oysters, seeds, crab, wheat germ, dried fruit, whole
cells; is needed for utilization of iron grains, legumes
Selenium Functions in association with vitamin E; may assist in Nuts, whole grains, lean pork, cottage cheese, milk,
protecting tissues and plasma membranes from oxidative molasses, squash
damage; may also aid in preventing cancer
Chromium Is required for maintaining normal glucose metabolism; may Nuts, prunes, vegetable oils, green peas, corn, whole
assist insulin function grains, orange juice, dark green vegetables, legumes
Manganese Is needed for normal bone structure, reproduction, and the Whole grains, nuts, seeds, pineapple, berries, legumes,
normal functioning of the central nervous system; is a dark green vegetables, tea
component of many enzyme systems
Molybdenum Is a component of enzymes; may help prevent dental caries Tomatoes, wheat germ, lean pork, legumes, whole
grains, strawberries, winter squash, milk, dark green
vegetables, carrots
Source: From David C. Nieman, et al., Nutrition, Revised 1st ed. Copyright © 1992 Wm. C. Brown Communications, Inc., Dubuque, Iowa.
No, it isn’t quite as interesting as your morning newspaper, but there’s for tissue growth and repair. Children and women who are pregnant
important information tucked into the corner of your Aqua Puffs (and or nursing should increase daily protein intake to support their body’s
all other packaged food). Reading nutrition labels, like the one shown rapid growth.
in Fig. 15A, should become a habit for anyone interested in health and
wellness. You’ll find the nutritional breakdown for a single serving Vitamins and Minerals
(in this example, a serving is 1 cup, or 57 grams) on these labels. Vitamins are organic molecules required in small amounts for good
Labels also tell us what share of daily nutrients and Calories is found health. Antioxidant vitamins (A, C, E, and beta-carotene) can
in that serving, based on a diet of 2,000 Calories. Calories are a mea- neutralize free radicals, unstable molecules generated during cellular
surement of food energy. As you can see, one serving of the cereal metabolism. Free radicals damage cell components and are linked to
provides 220 Calories. cancer and atherosclerosis. Calcium, iron, and sodium are important
minerals to consider. Calcium is required for bone manufacture, blood
Carbohydrates clotting, and proper nerve function, and iron is needed for hemoglo-
When studying nutrition labels, check carbohydrate content first. Car- bin. However, sodium consumption should be limited: Excess sodium
bohydrates are the most readily available energy source, and the best can worsen hypertension.
source for brain and nerve tissue. Sugar molecules are simple carbo- Bottom line: How nutri-
hydrates. Complex carbohydrates found in breads, cereals, vegeta- tious is that bowl of Aqua
bles, and fruits have the highest dietary fiber content. Fiber is found in Puffs? It’s a low-fat, high-
two forms, and each has distinct health benefits: Soluble fiber com- fiber cereal with no choles-
bines with cholesterol, preventing it from being absorbed, while terol or saturated fat. It
insoluble fiber has a laxative effect. Current recommendations include provides 80% of daily dietary Nutrition Facts
25 to 30 grams of fiber daily.
1
Serving Size: 1 cup (57 g)
iron, and 10% of vitamin C, 4
Servings per container: 8
essential for health. Fat is needed for energy, vitamin absorption, cereal will be a decent quick Saturated fat: 0g 0%
Cholesterol: 0 mg 0%
and for manufacturing cell lipids and steroids. However, any excess breakfast. But all that Sodium: 320 mg 13%
nutrient energy is stored as fat, which could ultimately lead to sugar—11 grams! It’s bound Total Carbohydrate: 46 g 15%
obesity. Further, nutrition research continues to prove the danger of to be tasty for someone with Soluble fiber: less than 1 g 0%
Insoluble fiber: 6 g 24%
excess saturated fat, and even worse are the artificially created a sweet tooth, but simple Sugars: 11 g
trans-fats. High saturated fat levels have been implicated in colon, sugars add Calories. Further, Other carbohydrates: 28 g
Protein: 5 g 11%
pancreas, ovary, prostate, and breast cancers. Saturated fat and you’d probably still need a
Vitamin A — 0% • Vitamin C — 10%
cholesterol contribute to atherosclerosis, the major cause of vitamin supplement. A Calcium — 0% • Iron — 80%
hypertension (high blood pressure), heart attack, and stroke in the breakfast of fresh fruit, along 2,000
Calories
Western world. (Atherosclerosis is described on pages 267–268.) with a no-fat dairy (or per-
Total fat
Saturated fat
Less than
Less than
65 g
20 g
Cholesterol Less than 300 mg
Better choices for fat intake would be monosaturated and polyun- haps soy) product for pro- Sodium
Total carbohydrate
Less than 2,400 mg
300 g
saturated plant fats such as canola and olive oils. Regardless of the tein, would be a better way to
Dietary fiber
Calories per gram:
25 g
fat type, a 2,000 daily Calorie diet should have no more than match the cereal’s nutrients
Fat 9 • carbohydrate 4 • protein 4
It’s a final measure sought by increasing numbers of people: bariatric laparoscope to illuminate structures in the abdomen. A band is placed
surgery, or surgical intervention with the specific goal of causing around the stomach. Once tightened like a belt, the stomach is divided
drastic weight loss. For many overweight people, years of dieting into a smaller upper chamber, which receives food, and a lower cham-
haven’t worked. Name a diet plan, and they have tried it—sure, they ber that remains connected to the duodenum. The belt can later be
lose weight, only to regain it. Obesity is approaching epidemic levels tightened further, or removed if necessary. In Roux-en-Y gastric
in the United States, with more than 78 million adults classified as bypass, the top section of the stomach is cut free and stapled shut to
obese. In addition, pediatricians are especially concerned with the make a pouch about the size of an egg. The small intestine is cut free
dramatic rise in childhood and teenage obesity. between the duodenum and jejunum, and the jejunum is sewn to the
Obesity is defined as a body mass index (BMI) greater than 30,1 or end of the stomach pouch. Finally, the duodenal segment is sewn back
a weight that is 41% or more higher than the ideal weight for one’s to the jejunum (forming the Y-shaped branch for which the procedure
height. It’s a physical and emotional challenge for the overweight patient. is named). The lower stomach and duodenum remain healthy and con-
Obesity is a primary risk factor for hypertension, type II diabetes melli- tinue to secrete digestive enzymes, but never receive food. Regardless
tus, atherosclerosis, stroke, coronary artery disease, and early heart of the approach used, the person will only be able to eat small amounts
attack. It has been linked to increased risk of breast, ovarian, uterine, and of food, but should feel full due to the small size of the stomach after
prostate cancer. Obese individuals suffer disrespect and ridicule from surgery. In addition, secretion of the gastric hormone ghrelin decreases
society and discrimination on the job. After years of struggling with the after surgery, and that often diminishes the person’s appetite.
problem, many are willing to undergo surgery as a last-chance option. It’s important to note that bariatric surgery comes with extremely
However, reputable programs offering bariatric surgery have serious potential complications. Postoperative bleeding and infection
strict requirements for patients. To be admitted as a surgical candi- are risks of any surgical procedure. Blood clots in the legs can form
date, the patient must be morbidly obese (BMI greater than 40; or during hospitalization, causing pulmonary embolism or stroke. After
greater than 100 pounds over ideal weight) or have a BMI in the range gastric bypass, staple lines in the stomach can leak. In rare cases, the
of 35 to 39, along with a serious obesity-related health issue such as connection between the stomach pouch and jejunum narrows, requir-
diabetes or high blood pressure. Patients cannot have respiratory or ing additional corrective surgery. Worst of all, a small percentage of
cardiac problems that might complicate surgery. Most important, the patients die during the surgery itself. After surgery, vitamin and min-
patient must understand the risks of surgery as well as its benefits. eral deficiencies are possible.
Patients must also understand that lifestyle changes will be necessary Further, bariatric surgery offers no guarantees of permanent
even after successful surgery and recovery. Psychological and nutri- weight loss—patients can in fact regain any weight that is lost, even
tional counseling is usually required before surgery to prepare the with a drastically smaller stomach. However, with proper nutrition
patient for new eating habits and ways of thinking about food. Follow- and behavioral changes, bariatric surgery can result in dramatic
up counseling tracks the patient’s progress in adapting. weight loss and improvement to health.
The two most commonly used interventions are laparoscopic
weight in pounds
banding and the Roux-en-Y gastric bypass (Fig. 15B). The more con- 1
To calculate BMI, use the following formula: 3 703.
(height in inches) 3 (height in inches)
servative approach, laparoscopic banding, requires making a series of BMI is not always accurate in determining obesity. Other factors such as percent body fat may
small incisions around the stomach and using an instrument called a also need to be used.
stomach
stomach (bypassed)
pouch
Pregnancy crowds
digestive organs and
promotes heartburn and
constipation.
Summary
15.1 Anatomy of the Digestive System particles called nutrients, (3) nutrient swallowing. The salivary glands
The gastrointestinal tract consists of absorption, and (4) the elimination of send saliva into the mouth.
the mouth, pharynx, esophagus, indigestible wastes. Saliva contains salivary amylase,
stomach, small intestine, and large A. The oral cavity begins physical an enzyme that begins the
intestine. The functions of the diges- and chemical digestion. chemical digestion of starch.
tive system include (1) ingestion, B. The teeth chew the food and C. Both air and food pass through
(2) the breakdown of food into small the tongue forms a bolus for the pharynx.
Study Questions
1. List the organs of the alimentary canal, 4. Name the accessory digestive organs, 8. What is the chief contribution of
and state the contribution of each to and describe the part they play in the each of these constituents of the
the digestive process. (pp. 343–350) digestion of food. (pp. 353–355, 358) diet: (a) carbohydrates; (b) proteins;
2. Discuss the absorption of the products 5. Name and discuss any three functions (c) fats; (d) fruits and vegetables?
of digestion into the lymphatic and of the liver. (pp. 355, 358) (pp. 361–362)
cardiovascular systems. (pp. 349–350, 6. Discuss the digestion of starch, pro- 9. What role do water-soluble
358–359) tein, and fat, listing all the steps that vitamins usually play in the body?
3. Name and state the functions of the occur with each. (pp. 358–360) (pp. 362–364)
hormones that assist the nervous sys- 7. How does the digestive system help 10. Name and discuss three eating disor-
tem in regulating digestive secretions. maintain homeostasis? (pp. 361, 368) ders. (pp. 365–366)
(pp. 350–351)
372
parasympathetic
fibers A sagittal section of a kidney shows that many branches of the
(involuntary) renal artery and renal vein reach inside a kidney (Fig. 16.3a). Re-
moving the blood vessels shows that a kidney has three regions
ureter (Fig. 16.3b). The renal cortex is an outer, granulated layer that
urinary trigone dips down in between a radially striated inner layer called the renal
bladder
medulla. The renal medulla consists of cone-shaped tissue masses
somatic nerve orifice of
(voluntary) ureter called renal pyramids. The renal pelvis is a central space, or cavity,
that is continuous with the ureter.
internal
sphincter
Anatomy of a Nephron
external sphincter Each kidney is composed of over one million nephrons, microscopic
urethra
structures that are the functional units of the kidney (Fig. 16.3d).
Figure 16.2 Urination. As the bladder fills with urine, There are two nephron types: cortical nephrons, which are shorter
sensory signals (blue arrows) go to the spinal cord and then to because they are located primarily in the cortex, and juxtamedul-
the brain. The brain can override the urge to urinate. When urina- lary nephrons, which extend deep into the medulla. A nephron con-
tion occurs, motor nerve signals (green arrows) cause the blad- sists of two combined structures: a renal corpuscle and a renal
der to contract and an internal sphincter to open. Nerve signals
tubule. The renal corpuscle is formed by the glomerulus, a tightly
also cause an external sphincter to open.
coiled capillary network, and the glomerular capsule (also called
Bowman’s capsule). The glomerular capsule is formed by the closed
end of the renal tubule, which widens to form a cuplike structure
Urination that surrounds the glomerulus. The blood supply of a nephron is un-
When the adult urinary bladder fills to about 250 ml with urine, usual because it contains two distinct capillary regions (Fig. 16.4).
stretch receptors send sensory nerve signals to the spinal cord. Sub- The nephron receives oxygenated arterial blood from an afferent
sequently, parasympathetic motor nerve signals from the lumbar arteriole, which originates from a smaller branch of the renal artery.
and sacral regions of the spinal cord cause the urinary bladder to The afferent arteriole leads to the glomerulus, the first capillary
contract and the sphincters to relax so that urination, also called bed. Blood leaves the glomerulus through the efferent arteriole. The
micturition, is possible (Fig. 16.2). In older children and adults, the efferent arteriole takes blood to the second capillary bed, called
brain controls this reflex, delaying urination until a suitable time. the peritubular capillary network, which surrounds the remain-
ing renal tubule. A specialized section of the peritubular capillary
network, the vasa recta, helps to maintain solute concentration in
Content CHECK-UP! the renal medulla, and will be detailed later. From the peritubular
capillary network, the blood goes into a venule. Venules join larger
1. Which is an enzyme produced by the kidney?
veins that ultimately empty into the renal vein.
a. renin c. erythropoietin
b. angiotensin d. aldosterone Parts of a Renal Tubule
2. Describe the way in which the kidneys and lungs interact to Each renal tubule is made up of several parts, beginning with the
control blood pressure. What chemicals are involved? glomerular capsule. This wide proximal end of the tubule surrounds
3. If you were to describe the urinary system, you could say: the glomerulus and receives the fluid it filters. The inner layer of
a. The kidneys are in the lumbar region. the glomerular capsule is composed of podocytes that have long,
b. The urinary bladder sits in the pelvic cavity. cytoplasmic extensions. The podocytes cling to the capillary walls of
the glomerulus and leave pores that allow easy passage of small mol-
c. The urethra transports urine from the kidney to the urinary
bladder. ecules from the glomerulus to the inside of the glomerular capsule.
Next, there is a proximal convoluted tubule (PCT), called
d. Only a and b are correct.
“proximal” because it is near the glomerular capsule. The cuboidal
e. All three statements are correct. epithelial cells lining this part of the nephron have numerous micro-
Answers in Appendix A. villi about 1 μm in length. These microvilli are tightly packed and
form a brush border, increasing the surface area for reabsorption.
renal
medulla
d. Nephrons
a. Blood vessels
renal cortex
renal pyramid
in renal medulla
renal pelvis
ureter
renal pyramid
in renal medulla
Figure 16.3 Gross anatomy of the kidney. (a) A sagittal section of the kidney showing the blood supply. Note that the renal
artery divides into smaller arteries, and these divide into arterioles. Venules join to form small veins, which join to form the renal vein.
(b) Sagittal section photograph of the kidney. (c) The same section without the blood supply. Now it is easier to distinguish the renal
cortex, the renal medulla, and the renal pelvis, which connects with the ureter. The renal medulla consists of the renal pyramids.
(d) An enlargement showing the placement of nephrons.
Simple squamous epithelium appears as the tube narrows and they touch is called the juxtaglomerular apparatus. (It is illus-
makes a U-turn called the loop of Henle. Each loop consists of a trated in Fig. 16.8, and its function will be described in section
descending limb and an ascending limb. 16.3.) The distal convoluted tubules of several nephrons enter a
The cuboidal epithelial cells of the distal convoluted tubule single collecting tubule. In turn, collecting tubules empty into
(DCT) have numerous mitochondria, but they lack microvilli. larger collecting ducts. Many collecting ducts carry urine to the
This is consistent with the active role they play in moving mol- renal pelvis.
ecules from the blood into the tubule, a process called tubular As shown in Figure 16.4, the glomerular capsule and the
secretion. Within the nephron, the distal convoluted tubule is convoluted tubules always lie within the renal cortex. The loop
generally adjacent to the afferent arteriole. The region where of Henle dips down into the renal medulla; juxtamedullary
proximal distal
glomerular capsule convoluted convoluted
(Bowman's capsule) tubule tubule
efferent arteriole
glomerulus
afferent arteriole
efferent
arteriole glomerulus
b.
distal
convoluted tubule
afferent arteriole
proximal
convoluted tubule
peritubular glomerular
venule capillary capsule
network
renal
artery c. 503
descending
renal vein limb ascending limb
descending limb
Loop of ascending
limb collecting duct
Henle collecting duct
vasa recta
capillaries
d. 1003
Renal Medulla
Figure 16.4 Nephron anatomy. (a) A nephron is made up of a glomerular capsule, the proximal convoluted tubule, the loop
of Henle, the distal convoluted tubule, and the collecting duct. Trace the path of blood around the nephron by following the arrows.
(b) Scanning electron micrograph shows a surface view of the glomerulus and its blood supply: the arterioles and peritubular capillary.
(c) Photomicrograph of cross section of the glomerulus. Notice that the convoluted tubules are just adjacent to it. (d) Photomicrograph of
cross sections of ascending and descending limbs of the loop of Henle, and peritubular capillaries.
nephrons have a very long loop of Henle, which penetrates inside of the glomerular capsule. This is a filtration process because
deep into the renal medulla. Collecting ducts are also located in large molecules and formed elements are unable to pass through the
the renal medulla, and they give the renal pyramids their lined capillary wall. In effect, then, blood in the glomerulus has two por-
appearance. tions: the filterable components and the nonfilterable components:
Filterable Nonfilterable
Urine Formation Blood Components Blood Components
Figure 16.5 gives an overview of urine formation, which is divided Water Formed elements (blood
into these steps: glomerular filtration, tubular reabsorption, and Nitrogenous wastes cells and platelets)
tubular secretion. Small molecules of nutrients Large plasma proteins
Salts (ions)
Creatinine and urochrome
Glomerular Filtration
Glomerular filtration occurs when whole blood enters the affer- The glomerular filtrate contains small, dissolved molecules found
ent arteriole and the glomerulus. Due to glomerular blood pressure, in approximately the same concentrations as their plasma concen-
water and small molecules are pushed from the glomerulus to the trations. Small molecules that escape being filtered as well as the
glomerular capsule
Glomerular filtration
H2O
urea Water, salts, ions, nutrient molecules,
and waste molecules move from the
glucose glomerulus to the inside of the glomerular
capsule. These small molecules are
amino called the glomerular filtrate. Tubular reabsorption
acids Nutrient and salt molecules and ions are
both passively and actively reabsorbed from
uric the ascending limb of the loop of Henle and
acid glucose, drugs, ammonia,
proximal the convoluted tubules into the peritubular
water, amino H1
salts convoluted capillary network, and water flows passively.
acids, salts
tubule
glomerulus
efferent
arteriole NaCl, water
H1
Tubular secretion
Certain ions and molecules (e.g., H1
and penicillin) are actively secreted from
the peritubular capillary network into the
convoluted tubules.
afferent
arteriole
end of another
distal tubule
renal distal
artery convoluted
tubule
renal
vein
venule
urea
collecting
duct
Water and salts peritubular
diffuse together capillary
into the vasa network
recta, where they
re-enter the blood
as plasma. H2O
urea
uric acid
loop of Henle salts
vasa recta NH41
creatinine
Figure 16.5 Steps in urine formation. Top: The three main steps in urine formation are described in boxes that are
color-coded to arrows showing the movement of molecules into or out of the nephron at specific locations. In the end, urine is
composed of the substances within the collecting duct (see brown arrow, lower right).
of the Kidneys
7. Describe how the kidneys help maintain the fluid and electrolyte
balance of blood. tissue
8. Name and explain how three hormones—aldosterone, antidiuretic fluid
hormone, and atrial natriuretic hormone—work together to maintain plasma
blood volume and pressure.
9. Describe three mechanisms, including how the kidneys function, to lymph
maintain the acid–base balance of blood.
other
The kidneys are involved in maintaining the blood’s fluid and elec-
trolyte balance, and also the acid–base balance. If the kidneys fail
to carry out these vital functions, either hemodialysis or a kidney
transplant is needed.
intracellular fluid (63%)
cortex NaCl
Antidiuretic hormone (ADH) produced by the hypothalamus,
Outer NaCl NaCl
H2O
and released by the posterior lobe of the pituitary, plays a role
medulla
in water reabsorption from the distal convoluted tubule and col-
lecting duct. In order to understand the action of this hormone,
H2O NaCl
consider its name. Diuresis means flow of urine, and antidiuresis
means against a flow of urine. In practical terms, if an individual
H2O NaCl H2O
does not drink much water on a given day, the hypothalamus will
H2O detect an increase in the osmotic pressure of the blood (i.e., the sol-
H2O utes in the blood will become more concentrated). As an analogy,
ascending
descending
d limb imagine leaving a glass of salt water on a windowsill for a week or
limb more. The salt will become more concentrated over time because
urea water is lost by evaporation. In the same way, blood solutes become
vvasa recta
more concentrated if the water lost daily isn’t replaced by drink-
ing. In response to increased blood osmolarity, the hypothalamus
Inner collecting
medulla loop of Henle duct will produce ADH, which is then released from the posterior pitu-
itary. ADH is transported to the cells of the collecting duct. There,
it causes specialized cell membrane channels called aquaporins
Figure 16.7 Reabsorption of water at the loop of to open. Water diffuses from the collecting duct to the interstitial
Henle and the collecting duct. A hypertonic environment in the space of the kidney through these aquaporins. Thus, more water is
tissues of the medulla of a kidney draws water out of the de- reabsorbed into the blood, blood volume and blood pressure rise,
scending limb and the collecting duct. This water is returned to and less urine is formed. On the other hand, if an individual drinks
the cardiovascular system. The thick black line means the ascend-
a large amount of water and does not perspire much, ADH is not
ing limb is impermeable to water. In the distal convoluted tubule
released. Collecting duct aquaporins remain closed, more urine
and collecting duct, water permeability is hormone dependent.
forms, and more water is excreted.
proximal
convoluted glomerular
tubule capsule
podocyte
afferent
arteriole
glomerulus
juxtaglomerular
apparatus
collecting duct
distal
convoluted
distal efferent tubule
convoluted arteriole
tubule
b.
a.
Figure 16.8 Juxtaglomerular apparatus. (a) This
drawing shows that the afferent arteriole and the distal convoluted
tubule usually lie next to each other. The juxtaglomerular appara-
tus occurs where they touch. (b) The juxtaglomerular apparatus
secretes renin, a substance that leads to the release of aldoste-
rone by the adrenal cortex. Reabsorption of sodium ions followed
by water then occurs. Therefore, blood volume and blood pres-
sure increase.
Acid–Base Buffer Systems These reactions temporarily prevent any significant change in
Normally, the pH of the blood stays near 7.4 because the blood is blood pH. A blood buffer, however, can be overwhelmed unless
buffered. A buffer is a chemical or a combination of chemicals that some more permanent adjustment is made. The next adjustment to
can take up excess hydrogen ions (H1) or excess hydroxide ions keep the pH of the blood constant occurs at pulmonary capillaries.
(OH2). Proteins are the primary buffers of both the intracellular
and extracellular fluid. Their amino acids can combine with or Respiratory Regulation of Acid–Base Balance
release hydrogen ions as needed. One of the most important buffers As discussed in Chapter 14, the respiratory center in the medulla
in the blood is a combination of carbonic acid (H2CO3) and bicar- oblongata increases the breathing rate, as well as the depth of res-
bonate ions (HCO32). Carbonic acid is a weak acid that minimally piration, if the hydrogen ion concentration of the blood rises. This
dissociates and re-forms in the following manner: change rids the body of hydrogen ions because the following reac-
tion takes place in pulmonary capillaries:
H2CO3 dissociates H+ + HCO3–
carbonic re-forms hydrogen bicarbonate
acid ion ion H+ + HCO3– H2CO3 H2O + CO2
When hydrogen ions (H1) are added to blood, the following reac-
tion occurs: In other words, when CO2 is exhaled, H1 ions recombine with HCO32
ions to form carbonic acid. Carbonic acid then dissociates, forming
H+ + HCO3– H2CO3 more carbon dioxide to be exhaled. H1 ions are now no longer free in
solution, but tied up harmlessly with water. Increasing respiratory rate
provides a rapid way to remove excess free H1 ions from blood. In
When hydroxide ions (OH2) are added to blood, this reaction occurs: contrast, when blood H1 falls, respiration decreases (hypoventilation),
allowing CO2 to build up. More H1 is produced and balance is restored.
OH– + H2CO3 HCO3– + H2O It is important to have the correct proportion of carbonic
acid and bicarbonate ions in the blood. Breathing readjusts this
pump
blood semipermeable
tubing
blood flow
dialysate
flow
dialysate
Figure 16.10 An artificial kidney machine. As the patient’s blood is pumped through dialysis tubing, it is exposed to a dialysate
(dialysis solution). Wastes exit from blood into the solution because of a preestablished concentration gradient. In this way, blood is
not only cleansed, but its water–salt and acid–base balances can also be adjusted.
salt molecules pass from the blood vessels in the abdominal wall is 97% if the kidney is received from a relative and 90% if it is
into the dialysate before the fluid is collected four or eight hours received from a nonrelative. Even with a successful surgery, the
later. The solution is drained into a bag from the abdominal cavity transplant patient must take antirejection medication for the rest
by gravity, and then it is discarded. One advantage of CAPD over of his or her life.
an artificial kidney machine is that the individual can go about
his or her normal activities during CAPD. However, CAPD is not
appropriate for all patients with renal failure. Because the abdomi- Content CHECK-UP!
nal cavity has a permanent opening, the patient must be carefully
10. Which are not normally found in urine? Choose all that apply.
trained and very diligent with sterile technique to avoid causing
abdominal infection (peritonitis). a. hydrogen ions d. urochrome
b. proteins e. creatinine
c. glucose
Renal Transplantation
11. Dialysis is used to treat:
Patients with renal failure sometimes undergo a kidney trans-
a. diabetes mellitus. c. kidney failure.
plant operation, during which a functioning kidney from a donor
is received. As with all organ transplants, there is the possibility b. high blood pressure. d. kidney stones.
of organ rejection. Receiving a kidney from a close relative has Answers in Appendix A.
the highest chance of success. The current one-year survival rate
The prostate gland, which is part of the male reproductive system, be used, and there are several belonging to this category: terazosin,
surrounds the urethra at the point where the urethra leaves the urinary doxazosin, tamsulosin, alfuzosin. All relax muscle tissue in the pros-
bladder. The prostate gland produces and adds a fluid to semen as tate. However, these drugs do not shrink the prostate. Often, treatment
semen passes through the urethra within the penis. At about age 50, involves using combinations of drugs from each category.
a man’s prostate often begins to enlarge, growing from the size of a If medication fails to help relieve the symptoms of BPH, a more
walnut to that of a lime or even a lemon. This condition is called invasive procedure can reduce the size of the prostate. Prostate tissue can
benign prostatic hyperplasia (BPH). Prostate enlargement is due to be destroyed by applying microwaves to a specific portion of the prostate,
a prostate enzyme called 5-alpha reductase. This enzyme acts on the or by using laser or ultrasound. In many cases, however, a physician may
male hormone testosterone, converting it into a substance that pro- decide that prostate tissue should be removed surgically. Rather than per-
motes prostate growth. That growth is normal during puberty, but forming abdominal surgery, which requires an incision in the abdomen,
continued growth in an adult is undesirable. As it enlarges, the pros- the physician can often access the prostate via the urethra in an operation
tate squeezes the urethra, causing urine to back up—first into the called transurethral resection of the prostate (TURP). This commonly
bladder, then into the ureters, and finally, perhaps, into the kidneys. used procedure is successful in approximately 97% of patients.
If the bladder can’t be completely emptied, the patient is at risk for Many men are concerned that BPH may be associated with pros-
infection and formation of kidney stones. tate cancer, but the two conditions are not necessarily related. BPH
The treatment for BPH begins by taking dietary supplements or occurs in the inner zone of the prostate, while cancer tends to develop
drugs that are expected to shrink the prostate and/or improve urine flow. in the outer area. If prostate cancer is suspected, blood tests and a
The first, saw palmetto, is sold in tablet form as an over-the-counter biopsy, in which a tiny sample of prostate tissue is surgically removed,
nutrient supplement. It is believed to interfere with the action of 5-alpha will confirm the diagnosis.
reductase. It should not be taken without medical supervision, but it is Although prostate cancer is the second most common cancer in
particularly effective during the early stages of prostate enlargement. men, it is not a major killer. Typically, the most common form of prostate
The prescription drugs finasteride and dutasteride are more powerful cancer is so slow growing that the survival rate is about 98% if the condi-
inhibitors of the enzyme, but erectile dysfunction and loss of libido are tion is detected early. Treatment typically consists of surgery to remove
common side effects. Drugs called alpha-adrenergic blockers can also the prostate, along with radiation therapy and/or chemotherapy.
16.5 Effects of Aging than half that of a young adult and often contains residual urine.
Therefore, urination is more urgent and frequent.
12. Describe the anatomical and physiological changes that occur in the
urinary system as we age.
Content CHECK-UP!
Urinary disorders are significant causes of illness and death among
12. Many changes occur in the kidneys as people age. The
the elderly. Total renal function in an elderly individual may be only
change that seems to affect renal efficiency most is:
50% of that of the young adult. With increasing age, the kidneys
decrease in size and have significantly fewer nephrons. However, a. degenerating glomeruli.
vascular changes may play a more significant role in declining b. improper diet and fluid intake.
renal efficiency than renal tissue loss. Microscopic examination c. kidney stones.
shows many degenerate glomeruli through which blood no longer d. prostate problems.
flows and many other glomeruli that are completely destroyed. Answer in Appendix A.
Kidney stones occur more frequently with age, possibly as a
result of improper diet, inadequate fluid intake, and kidney infec-
tions. Infections of the urethra, bladder, ureters, and kidneys in-
crease in frequency among the elderly. Enlargement of the prostate 16.6 Homeostasis
occurs in males and, as is discussed in the Medical Focus, Prostate 13. Describe how the urinary system works with other systems of the
Enlargement and Prostate Cancer, this can lead to urine retention body to maintain homeostasis.
and kidney disease. Cancer of the prostate and bladder are the most
common cancers of the urogenital system. The illustration in Human Systems Work Together on page 388
The involuntary loss of urine, called incontinence, increases tells how the urinary system works with the other systems of the
with age. The bladder of an elderly person has a capacity of less body to help maintain homeostasis.
Summary
16.1 Urinary System tubule have many mitochondria respiratory center has regulated
A. The kidneys excrete nitrogenous and microvilli to carry out reab- the breathing rate to control the
wastes, including urea, uric acid, sorption, which is active transport excretion of carbon dioxide at
and creatinine. They maintain from the tubule to the blood. In pulmonary capillaries. The kid-
the normal water–salt balance, contrast, the cuboidal epithelial neys largely control acid–base
blood pressure, and acid–base cells of the distal convoluted tu- balance by excreting hydrogen
balance of the blood, as well as bule have numerous mitochondria ions and reabsorbing bicarbon-
influencing the secretion of but lack microvilli. They carry out ate ions as needed.
certain hormones. secretion, which is active trans- 16.4 Problems with Kidney Function
B. The kidneys produce urine, port from the blood to the tubule. Various types of urinary problems,
which is conducted by the ure- C. The steps in urine formation are including repeated urinary infec-
ters to the bladder, where it is glomerular filtration, tubular tions, can lead to renal failure.
stored before being released by reabsorption, and tubular A. Hemodialysis uses machines to
way of the urethra. secretion. mimic the function of the kidneys
C. Urine is eliminated from the 16.3 Regulatory Functions of the Kidneys by removing wastes from the
body via a reflex called micturi- A. The kidneys regulate the fluid blood. Some patients use CAPD
tion. Stretch receptors in the wall and electrolyte balance of the to cleanse their blood.
of the urinary bladder begin this body. Water comes into the body B. Patients in kidney failure might
reflex, which ends in the relax- by drinking, in food, and as a by- undergo a kidney transplant.
ation of two urinary sphincters: product of metabolism. Water Success rates of this procedure
the internal sphincter, made of leaves the body through urine, are high, especially when donors
smooth muscle, and the external sweat, exhalation, and feces. and recipients have similar tis-
sphincter, which is made of B. Water is reabsorbed from certain sue types and immunosuppres-
skeletal muscle. parts of the tubule, and the loop of sant drugs are used.
16.2 Anatomy of the Kidney and Excretion Henle establishes an osmotic gra- 16.5 Effects of Aging
Macroscopically, the kidneys are di- dient that draws water from the Kidney function declines with age.
vided into the renal cortex, renal descending loop and also from Also, kidney stones, infections,
medulla, and renal pelvis. the collecting duct. The permeabil- and urination problems are more
A. Microscopically, the kidneys con- ity of the collecting duct is under common.
tain nephrons. Each nephron has the control of the hormone ADH. 16.6 Homeostasis
its own blood supply. Blood in the C. The reabsorption of salt in- The kidneys work with other organs
afferent arteriole flows into the creases blood volume and pres- in the body to excrete wastes. The
glomerulus, a knot of capillaries. sure because more water is also sweat glands of the integumentary
Blood in the efferent arteriole reabsorbed. Two other hor- system excrete excess water, salts,
flows out of the glomerulus and mones, aldosterone and ANH, and urea. The liver excretes prod-
immediately enters the peritubular control the kidneys’ reabsorption ucts of the breakdown of hemoglo-
capillary network. of sodium (Na1) and water and bin, while the lungs excrete carbon
B. Each region of the nephron is ana- the secretion of potassium (K1). dioxide. The kidneys are the primary
tomically suited to its task in urine D. The kidneys regulate the acid– organs of homeostasis: they main-
formation. The spaces between base balance of the blood. tain water–electrolyte balance and
the podocytes of the glomerular Before the work of the kidneys acid–base balance. These in turn af-
capsule allow small molecules to begins, the acid–base buffer fect blood volume and blood pres-
enter the capsule from the glom- systems of the blood have func- sure. The kidneys also act as
erulus. The cuboidal epithelial tioned to keep the pH temporar- endocrine organs to secrete renin
cells of the proximal convoluted ily under control; also, the and erythropoietin.
PART V
The Reproductive System
Learning Outcomes After you have studied this chapter, you should be able to:
17.1 Human Life Cycle 17.3 Female Reproductive System 17.6 Homeostasis
1. Discuss the functions of the 9. Describe the macroscopic and 17. Discuss how the reproductive
reproductive system. microscopic anatomy of the ovaries. system works with other systems of
2. Describe the human life cycle. 10. Label a diagram of the external the body to maintain homeostasis.
female genitals.
17.2 Male Reproductive System 11. Contrast female orgasm with male Visual Focus
3. Trace the path of sperm, from the orgasm. Anatomy of Ovary and Follicle
testes to the urethra. 12. Describe the menstrual cycle.
4. Describe the macroscopic and 13. Describe the actions of estrogen and Medical Focus
microscopic anatomy of the testes. progesterone, including both primary Ovarian Cancer
5. Name the glands and describe the and secondary sexual characteristics.
Breast and Testicular Self-Exams for Cancer
secretions that contribute to the
composition of semen. 17.4 Control of Reproduction and Endocrine-Disrupting Contaminants
6. Describe the anatomy of the penis Sexually Transmitted Infections Preventing Transmission of STIs
and the events preceding and during 14. List several means of birth control,
ejaculation. and describe their effectiveness. Human Systems Work Together
7. Discuss hormonal regulation in the 15. Describe the symptoms of genital Reproductive System
male. warts, genital herpes, hepatitis,
8. Outline the actions of testosterone, chlamydia, gonorrhea, and syphilis. Focus on Forensics
including its effects on the primary Rape
sex organs and secondary sexual 17.5 Effects of Aging
characteristics.
16. Discuss the anatomical and
physiological changes that occur in
the reproductive system as we age.
392
Spermatocyte
92 Oocyte
prophase II
Chromosomes
primary cell
(46
pairs)
meiosis I
metaphase II
46 46
Chromosomes Chromosomes
secondary cell
(23 (23
pairs) pairs)
meiosis II
anaphase II
23 23 23 23 completed
Chromosomes Chromosomes Chromosomes Chromosomes haploid (n)
gamete
a. telophase II
b.
Figure 17.2 Meiosis (a) Prior to meiosis, the ovaries in females and testes in males produce large quantities of oogonia/sper-
matogonia by mitosis. Primary cells will divide to form two secondary cells; secondary cells divide further to form four haploid cells. In this
way, the chromosome number is reduced from 92, to two sets of 46 chromosomes, to four sets of 23 chromosomes. (b) The stages in
meiosis are the same as mitosis (prophase, metaphase, anaphase, telophase) except that they occur twice. Note that during prophase I,
the paired chromosomes in a tetrad can exchange genetic information with one another.
erectile tissue
of penis
urethra
penis anus
vas deferens
glans penis epididymis
prepuce
testis
scrotum
Figure 17.3 Male reproductive system. The testes produce sperm. The seminal vesicles, the prostate gland, and the
bulbourethral glands provide a fluid medium for the sperm, which move from a testis to an epididymis to a vas deferens and through the
ejaculatory duct to the urethra in the penis. The foreskin (prepuce) is removed when a penis is circumcised.
the testis, forming septa, or walls, that divide the testis into compart- (Sertoli) cells. Sustentacular cells are large; they extend from the
ments called lobules. Each lobule contains one to three tightly coiled capsule to the lumen of the seminiferous tubule. The sustentacular
seminiferous tubules (Fig. 17.4a). Altogether, these tubules have cells support, nourish, and regulate the development of cells under-
a combined length of approximately 250 m. A microscopic cross going spermatogenesis.
section of a seminiferous tubule reveals that it is packed with cells The germ cells near the outer capsule are called
undergoing spermatogenesis (Fig. 17.4b), the production of sperm. spermatogonia. The spermatogonia divide, producing more
Delicate connective tissue surrounds the seminiferous tubules. cells by mitosis. Some of these cells remain as spermatogonia,
Cells that secrete the male sex hormones, the androgens, are which continue to divide. These provide a constant source of
located here between the seminiferous tubules. Therefore, these sperm cells throughout a normal man’s lifetime. Other spermato-
endocrine cells are called interstitial cells (also called interstitial gonia replicate their DNA and become primary spermatocytes,
cells of Leydig or, simply, Leydig cells). The most important of containing 92 sister chromatids (strands of DNA) held together
the androgens is testosterone, whose functions are discussed later in 46 pairs (Fig. 17.5). Primary spermatocytes are termed
in this section. diploid, or 2n cells. The primary spermatocytes start the process
Testicular cancer, or cancer of the testes, is one type of cancer of meiosis, which requires two divisions. Following meiosis I,
that can be detected by self-examination, as explained in the Medi- two secondary spermatocytes are formed, each containing 46
cal Focus on page 413. chromatids in 23 pairs. When meiosis II has been completed,
there are four spermatids, cells that are termed haploid because
they possess half the normal chromosome number. Spermatids
Spermatogenesis then mature into sperm.
Spermatogenesis, the production of sperm, includes the process of Mature sperm, or spermatozoa, have three distinct parts: a
meiosis as the sperm form. Before puberty, the testes, including the head, a middle piece, and a tail (see Fig. 17.4c). Mitochondria
seminiferous tubules, are small and nonfunctioning. At the time of in the middle piece provide energy for the movement of the tail,
puberty, the interstitial cells increase their size and start producing which has the structure of a flagellum. The head contains a nu-
androgens. Then, the seminiferous tubules also enlarge, and they cleus covered by a cap called the acrosome, which stores enzymes
start producing sperm. needed to penetrate the ovum. Notice in Figure 17.4b, that the
The seminiferous tubules contain two types of cells: germ sperm are situated so that their tails project into the lumen of the
cells, which are involved in spermatogenesis, and sustentacular seminiferous tubules.
Figure 17.4 Testis and sperm. (a) The lobules of a testis contain seminiferous tubules. (b) Micrograph showing a cross
section of the seminiferous tubules, where spermatogenesis occurs. (c) A sperm has a head, a middle piece, and a tail. The nucleus is in
the head, which is capped by the enzyme-containing acrosome.
When formed, the sperm are transported from the seminifer- Male Internal Accessory Organs
ous tubules into a complex network of channels that ultimately
Table 17.1 lists and Figure 17.6 depicts the internal accessory
form ducts. The ducts join to form the epididymis, which empties
organs, as well as the other reproductive organs, of the male. Sperm
into the vas deferens.
are transported to the urethra by a series of ducts. Along the way,
The ejaculated semen of a normal human male contains sev-
various glands add secretions to seminal fluid.
eral hundred million sperm, but only one sperm normally enters
an egg. Sperm typically survive in the female reproductive tract
for approximately 48 hours after sexual intercourse. However, Epididymides
under optimal conditions sperm can survive for 4–6 days after Each epididymis is a tightly coiled, threadlike tube that would
intercourse. stretch about 6 meters if uncoiled. An epididymis runs posteriorly
nucleus of
Sertoli cell
Figure 17.5 Spermatogenesis. Diploid spermatogonia reproduce by mitosis, and the two phases of meiosis result in
spermatids. Spermatids mature into functional sperm cells.
dorsal vein
dorsal artery
dorsal nerve
skin
corpora
cavernosa
connective
layers skin
Figure 17.7 Penis anatomy. (a) Beneath the skin and the connective tissue lies the urethra surrounded by erectile tissue.
This tissue expands to form the glans penis, which in uncircumcised males is partially covered by the foreskin (prepuce). (b) Two other
columns of erectile tissue in the penis are located posteriorly.
uterine tube
ovary fimbriae uterus
fimbriae
vagina
uterus
glans clitoris
Figure 17.9 The female
labium minora anus reproductive system. The ovaries
release one egg per month. Fertiliza-
labium majora
tion occurs in the uterine tube and de-
vaginal orifice velopment occurs in the uterus. The
vagina is the birth canal as well as the
organ of sexual intercourse.
Visual Focus
4. Ovulation: The
6. Corpus luteum
secondary oocyte is
degenerates. corpus released.
luteum 5. Corpus luteum produces
the sex hormones secondary
progesterone and some oocyte
estrogen.
Figure 17.10 Anatomy of ovary and follicle. As a follicle matures, the oocyte enlarges and is surrounded by layers of
follicular cells and fluid. The micrograph shows the mature vesicular (Graafian) follicle. Eventually, ovulation occurs, the mature follicle
ruptures, and the secondary oocyte is released. A single follicle actually goes through all the stages in one place within the ovary.
first polar
body first polar second polar fusion of
46 chromosomes body body sperm nucleus (n)
in 23 pairs 46 chromosomes 23 chromosomes and egg nucleus (n)
sperm
nucleus (n)
23 chromosomes
Figure 17.11 Oogenesis in an ovary. Oogenesis involves meiosis I, during which the chromosome number is reduced, and
meiosis II, which results in a single egg. Meiosis II takes place after a sperm enters the secondary oocyte. At the end of oogenesis, there
are also at least two polar bodies, nonfunctional cells that later disintegrate.
ovarian
vessels
ovarian ligament
uterine tube
fimbriae
ovary
body of uterus
broad ligament
ureter
cervix
vagina
external os
Ovarian cancer is often “silent,” showing no obvious signs or reported in the more industrialized countries, with the exception of
symptoms until late in its development. Rarely is there any abnor- Japan.
mal vaginal bleeding, as might be seen with uterine or cervical Early detection requires periodic, thorough pelvic examinations.
cancers. The most common sign is enlargement of the abdomen, The Pap smear, useful in detecting cervical cancer, does not reveal
which is caused by the accumulation of fluid. Vague symptoms ovarian cancer. Women over age 40 should have a cancer-related
may occur: bloating, pelvic or abdominal pain, difficulty eating check-up every year. Researchers are currently trying to develop a
and/or feeling full quickly, increased urinary frequency, and the blood test that will allow for consistent diagnosis of early ovarian
urgent need to urinate. When symptoms such as these persist in cancer. Testing for high levels of tumor marker CA-125, a protein
women over 40 (and if they cannot be explained by any other cause) antigen, is sometimes used to screen for ovarian cancer. However,
they may indicate the need for a thorough evaluation for ovarian CA-125 is unreliable because it gives false positive results for many
cancer. other disorders, including benign ovarian cysts and pregnancy. A
The risk for ovarian cancer increases with age. The highest rates combination of blood testing and ultrasound examination of the ova-
are for women over age 60. Women who have never had children are ries is currently the most accurate way to diagnose ovarian cancer.
twice as likely to develop ovarian cancer as those who have. Early age Surgery, radiation therapy, and drug therapy are treatment
at first pregnancy, early menopause, and the use of oral contracep- options. Surgery usually includes the removal of one or both ovaries
tives, which reduces ovulation frequency, appear to be protective (oophorectomy), the uterus (hysterectomy), and the uterine tubes
against ovarian cancer. If a woman has had breast cancer, her chances (salpingectomy). In some very early tumors, only the involved ovary
of developing ovarian cancer double. Certain rare genetic disorders is removed, especially in young women. In advanced disease, an
and usage of hormone replacement therapy are also associated with attempt is made to remove all intra-abdominal cancerous tissue to
increased risk. The highest incidence rates for ovarian cancer are enhance the effect of chemotherapy.
region superior to the entrance of the uterine tubes, and the body of Vagina
the uterus is the major region. The cervix is the narrow end of the The vagina is a tube that makes a 45° angle with the inferior lumbar
uterus that projects into the vagina. A cervical orifice, or opening, region (small of the back). The mucosal lining of the vagina lies
leads to the lumen of the vagina. in folds that extend when the fibromuscular wall stretches. This
Development of the embryo normally takes place in the uterus. capacity to extend is especially important when the vagina serves
This organ, sometimes called the womb, is approximately 5 cm as the birth canal, and it can also facilitate intercourse, when the
wide in its usual state but is capable of stretching to over 30 cm to vagina receives the penis.
accommodate the growing baby. The lining of the uterus, called
the endometrium, participates in the formation of the placenta (see
Chapter 18), which supplies nutrients needed for embryonic and External Genitals
fetal development. In the nonpregnant female, the endometrium The female external genitals (Fig. 17.13) are known collectively
varies in thickness during a monthly menstrual cycle, discussed as the vulva. The vulva includes two large, hair-covered folds of
later in this chapter. skin called the labia majora (sing., labium majus). They extend
Cancer of the cervix is a common form of cancer in women. posteriorly from the mons pubis, a fatty prominence underly-
The Medical Focus Immunization: The Great Protector in ing the pubic hair. The labia minora (sing., labium minus) are
Chapter 13 (pages 309–310) describes a vaccine that immu- two small folds of skin lying just inside the labia majora. They
nizes against the human papillomavirus that causes the major- extend forward from the vaginal opening to encircle and form
ity of human cervical cancers. Early detection is possible by a foreskin for the clitoris, an organ that is homologous to the
means of a Pap smear, which entails the removal of a few penis. Although quite small, the clitoris has a shaft of erectile
cells from the region of the cervix for microscopic examination. tissue and is capped by a pea-shaped glans. The clitoris also has
If the cells are cancerous, a hysterectomy (the removal of the sensory receptors that allow it to function as a sexually sensi-
uterus) may be recommended. Removal of the ovaries in addi- tive organ.
tion to the uterus is termed an ovariohysterectomy. Because The vestibule, a cleft between the labia minora, contains
the vagina remains intact, the woman can still engage in sexual the orifices of the urethra and the vagina. The vagina can be
intercourse. partially closed by a ring of tissue called the hymen. The hymen
Days 1 3 5 7 9 11 13 15 17 19 21 23 25 27 1
Gonadotropin levels
FSH
LH
Days 1 3 5 7 9 11 13 15 17 19 21 23 25 27 1
ovulation
estrogen
progesterone
Days 1 3 5 7 9 11 13 15 17 19 21 23 25 27 1
Uterine cycle
menstrual
flow
functional
layer
basal
layer
Days 1 3 5 7 9 11 13 15 17 19 21 23 25 27 1
Figure 17.15 Events of the menstrual cycle. During the menstrual cycle, FSH and LH are released by the anterior pituitary. FSH
promotes the maturation of a follicle in the ovary. The follicle produces increasing levels of estrogen, which cause the endometrium to thicken
during the proliferative phase in the uterus. An LH surge causes ovulation. After ovulation, LH promotes the development of the corpus
luteum. This structure produces increasing levels of progesterone, which causes the endometrial lining to become secretory. Menses due to
the breakdown of the endometrium begins when progesterone production declines to a low level due to corpus luteum disintegration.
intercostal muscles
pectoralis minor
pectoralis major
nipple
nipple
areola
mammary ducts rib
lobule containing
lobule alveoli
mammary ducts
a. Anteromedial view b. Sagittal view
Figure 17.16 Structure of the female breast and mammary glands. (a) Anteromedial view. (b) Sagittal section.
estrogen causes proliferation of ducts and that both estrogen and Breast cancer is one of the few types of cancer that can be de-
progesterone bring about alveolar development. The abundance of tected by the female herself. The Medical Focus on page 413 tells
these hormones during pregnancy means that the alveoli prolifer- how to do a monthly check for breast cancer.
ate at this time. A breast which does not produce milk has ducts
but few alveoli, while a lactating (milk-producing) breast has many
ducts and alveoli.
During pregnancy, the breasts enlarge as the ducts and Content CHECK-UP!
alveoli increase in number and size. The same hormones that
7. Which ovarian structure eventually releases the secondary
affect the mother’s breasts can also affect the child’s. Some new-
oocyte? Which produces progesterone? Which is scar tissue?
borns, including males, even secrete a small amount of milk for
How are they related?
a few days.
8. The second stage of meiosis in an ovum will only be com-
Usually, no milk is produced during pregnancy. The hor-
pleted if:
mone prolactin is needed for lactation (the process of milk
production) to begin. Prolactin formation is suppressed during a. it occurs before the ovum is released at ovulation.
pregnancy, because negative feedback control by high levels of b. it occurs after the ovum is released and travels through the
estrogen and progesterone shuts down prolactin secretion by the uterine tube.
anterior pituitary. Once the baby is delivered, however, the pitu- c. the ovum is fertilized by a sperm cell.
itary begins secreting prolactin. It takes a couple of days for milk d. it occurs just after the ovum is released from the ovary, but
production to begin, and in the meantime, the breasts produce before it enters the uterine tube.
colostrum, a thin, yellow, milky fluid rich in protein, including 9. During which stage of the monthly cycle of the uterus does
antibodies. the endometrium thicken and become glandular and
The continued production of milk requires a suckling child. vascular?
When a breast is suckled, the nerve endings in the areola are stimu- a. menstrual phase
lated, and a nerve impulse travels along neural pathways from the b. secretory phase
nipples to the hypothalamus, which directs the posterior pituitary
c. proliferative phase
gland to release the hormone oxytocin. When this hormone arrives
at the breast, it causes the lobules to contract so that milk flows into d. ovulation phase
the ducts (called milk letdown), where it may be drawn out of the Answers in Appendix A.
nipple by the suckling child.
lon96431_ch17_392-424.indd 411
Abstinence Refrain from sexual intercourse No sperm in vagina 100% None; also protects against sexually
transmitted infections
Natural family planning Determine day of ovulation by keeping Intercourse is avoided only during the 80-97% None (requires training for
records; various testing methods time period while ovum is viable symptothermal method to be
effective)
Withdrawal method Penis withdrawn from vagina just Ejaculation outside the woman’s body; 75% None
before ejaculation no sperm in vagina
Douching Vagina cleansed after intercourse Washes sperm out of woman’s body Less than 70% May cause infection or inflammation
NONPRESCRIPTION METHODS
Male condom Sheath of latex, polyurethane, or Traps sperm and prevents entry into 85% With latex: latex allergy; natural
natural material fitted over erect vagina; latex and polyurethane material condoms give no
penis forms protect against STIs protection against STIs
Female condom Synthetic latex fitted inside vagina Traps sperm and prevents entry into 79% Possible allergy or irritation; urinary
vagina; some protection against STIs tract infection
Spermicide: jellies, foams, Spermicidal products inserted into the Spermicidal chemical nonoxynol-9 50–80% Irritation, inflammation; allergic
films, creams, tablets vagina before intercourse kills large numbers of sperm cells reaction; urinary tract infection
Contraceptive sponges Sponge containing spermicide inserted Spermicidal chemical nonoxynol-9 72–86% Irritation, inflammation; allergic
into vagina and placed against kills large numbers of sperm cells reaction; urinary tract infection;
cervix toxic shock syndrome
411
Continued
18/11/15 4:19 PM
412
TABLE 17.3 Continued
Name Procedure How Does It Work? How Effective Is It? Side Effects and Other Health Risks
PRESCRIPTION HORMONAL METHODS
Progestin-only mini-pill Pills are swallowed daily Thickens cervical mucus, preventing 92% Irregular bleeding; weight gain;
lon96431_ch17_392-424.indd 412
sperm from contacting ovum; may breast tenderness
prevent implantation by embryo
Combined hormone 91, Pills are swallowed daily; user has 3–4 Suppresses ovulation by the 98% Dizziness, nausea; changes in
daily regimen menstrual periods a year combined actions of the menstruation, mood, and weight;
hormones estrogen and rarely: cardiovascular disease,
progestin; may prevent including high blood pressure,
implantation by embryo blood clots, heart attack, and
strokes
SURGICAL STERILIZATION
Vasectomy Vasa deferentia are cut and tied No sperm in seminal fluid Almost 100% Most likely irreversible; minor risk of
surgical complications such as
infection or reaction to anesthetic
Tubal ligation: Oviducts are cut and tied, or a clip is Sperm cannot enter oviduct; ova Almost 100% Most likely irreversible; pain,
transabdominal placed on the oviduct cannot pass through oviduct bleeding, infection; other
surgery post-surgical complications;
ectopic (tubal) pregnancy
Sterilization implant Small metallic implant is placed into Causes scar tissue to form, blocking Almost 100% Most likely irreversible; pain after
(Essure) uterine tubes; inserted through the uterine tubes and preventing placement; ectopic pregnancy
vagina using a catheter conception
18/11/15 4:19 PM
MEDICAL FOCUS
Breast and Testicular Self-Exams for Cancer
The American Cancer Society urges women to do a breast self-exam 5. If you find any changes during your self check-ups, try not to
and men to do a testicle self-exam every month. Breast cancer and panic. Finding that there’s a change doesn’t necessarily mean
testicular cancer are far more curable if found early, and either test you’ve got cancer. But see your physician or other health-care
takes less than half an hour. provider right away, just to be sure. Remember—if you find it
early, there’s an excellent chance that breast cancer can be cured.
Breast Self-Exam for the Ladies:
You should know that the best check for breast cancer is a mam-
1. Check your breasts for any lumps, knots, or changes about one week
mogram, which is a low-dose X ray of the breast tissue. When your
after your period. Don’t stand up to do the exam—be sure to lie
doctor checks your breasts, ask about getting a mammogram. Yearly
down on a flat surface. This will allow your breast tissue to spread
mammograms are recommended for women over 40 years of age.
evenly over your chest, so you can feel a change much more easily.
Women with a personal or family history of breast cancer (mother,
2. Place your right hand behind your head. Use the fingertips of
sister, or aunt who have or had the disease) may be advised to start
your middle three fingers for the test; they’re the most sensitive
such screening exams at an earlier age, and to have the exams more
part of your hand. Move your left hand over the right side of your
frequently. Additional exams such as ultrasound or MRI of the breast
chest in an up-and-down pattern. Begin at the edge of your arm-
may also be advised.
pit, tracing overlapping dime-sized circles all the way to the bot-
tom of your rib cage. Stroke up and down across your entire chest Testicle Self-Exam for the Guys:
from the armpit to the sternum (breastbone). As you move your
1. Check your testicles once a month, beginning right after puberty.
fingers across your chest, slide them from the top of your clavicle
It takes only a few minutes.
(collarbone) down to the bottom of your rib cage. Start with a
2. Do your check right after a warm bath or shower, so that the skin
very gentle pressure, so you can feel any lumps that might lie just
on your scrotum is relaxed. Hold your penis out of the way, and
under the skin. Gradually increase the pressure until you’re
check one testicle at a time. Roll each testicle between your
stroking firmly on the breast. Use each level of pressure before
thumb and finger as shown in Figure 17C. Feel for hard lumps or
you move onto another area (Fig. 17A).
bumps. A normal epididymis often feels like a lump on the out-
3. Now place your left hand behind your head and check your left
side of your testis, so get used to locating it.
breast with your right hand.
3. If you notice a change or have aches or lumps, try not to be too
4. Then, check your breasts while standing in front of a mirror
alarmed. There are many normal structures found in a testicle that
(Fig. 17B). First, put your hands firmly on your hips. Then,
may feel “lumpy,” including blood vessels and supporting tissues.
raise your arms above your head and stand up very straight so
But be sure to tell your doctor or other health-care professional right
you’re tightening your chest muscles and skin. Look for any
away if you’re concerned about any differences that you notice.
changes in the way your breasts look: changes in size or shape,
dimpling of the skin, changes in the nipple, redness, swelling, Testicular cancer is the most common solid tissue cancer in young
or abnormal discharge. men between the ages of 15 and 35, so doing a self-exam is very
important. Cancer of the testicles can be cured if you find it early. You
should also know that prostate cancer is the second most common
cancer in men (second only to skin cancer). Men over age 50 should
have an annual health checkup that includes a prostate examination.
One of the first synthetic estrogens to be produced in a laboratory was introduced into the environment via human sewage. Other chemicals
diethylstilbestrol, or DES, created in 1938. In the ensuing years, DES shown to influence hormones are found in plastics, food additives, and
was used to treat a variety of conditions such as prostate cancer in personal hygiene products. Baby bottles, plastic cups, and toys recently
men and menopausal symptoms in women. For a short time, it was have been discontinued from the market because compounds used for
even used as an emergency contraceptive. Tragically, DES was also hardening their plastic are suspected EDCs. In mice, some plastic com-
given to many pregnant women to prevent early miscarriage. Years ponents affect neonatal development when present in extremely low
later, those same women’s children are suffering from its effects on concentrations (parts per trillion). EDCs have been found in nature at
their reproductive systems. Daughters of the original patients (called levels 1,000 times greater than this—even in amounts comparable to
DES daughters) often have birth defects involving reproductive sys- functional hormone levels in the human body. It’s also important to rec-
tem organs, including the ovaries, uterus, and vagina. Further, these ognize that hormones and hormonelike contaminants are concentrated
same women are 2.5 times as likely to have breast cancer after age 40. in adipose tissue. Obesity, which is epidemic in the United States,
DES daughters are also more likely to suffer from cancers of the increases the risk that EDCs might be found at toxic levels in humans.
vagina and cervix. DES sons have an increased risk of genital abnor- Scientists and those representing industrial manufacturers con-
malities, and possibly prostate and testicular cancers as well. tinue to debate whether EDCs pose a health risk to humans. Currently,
The consequences of DES use have raised concern about the the EPA regulates the concentration of 23 inorganic chemicals includ-
many chemicals created after 1938 that might also affect the endo- ing mercury, lead, and arsenic, and more than 30 organic chemicals
crine system. Because endocrine hormones influence nearly all also are regulated. Doubtless other inorganic and organic chemicals
aspects of physiology and behavior in animals, synthetic compounds will be added to the list as research continues. In the meantime, there
called endocrine-disrupting contaminants (EDCs) that show hor- are steps you can take to minimize the dangers of EDCs:
monal effects are being studied extensively. Environmental biologists
first became aware of EDCs when wildlife—especially fish, amphib- • Maintain a healthy weight. Excess adipose tissue can contain
high levels of EDCs that you may have been exposed to through-
ians, reptiles, and birds in polluted areas—began to show abnormali-
out your life.
ties in tissue differentiation, sexual development, and reproduction.
Human studies suggest that these same pollutants lower sperm counts, • Use less plastic. Substitute reusable cloth bags, washable din-
nerware, glass containers, etc., for the plastic products you might
reduce male and female fertility, and increase the rates of certain can-
otherwise buy. In particular, avoid plastics marked 3, 6, or 7,
cers (breast, ovarian, testicular, and prostate). Further, EDCs are
because these types are the most likely to contain EDCs.
thought to be responsible for early onset of menses in young girls,
some of whom begin their periods as early as age 10. Additionally, • Recycle plastic, so that EDCs that might be contained in it don’t
leak into the groundwater.
some studies seem to indicate that EDCs contribute to learning defi-
• Don’t heat or reheat food in plastic containers.
cits and behavioral problems in children.
Many EDCs are chemicals used as pesticides and herbicides in • If you eat a lot of fish, be aware of those that may contain high
levels of EDCs and other contaminants. The EPA maintains a
agriculture, and some are associated with the manufacture of various
database that can help you find out which fish in your area are
other synthetic organic compounds such as PCBs (polychlorinated
safe to eat: http://www.epa.gov/waterscience/fish/
biphenyls). Oral contraceptives and other hormonal pharmaceuticals are
form, called the symptothermal method, uses two separate sets of unprotected intercourse. The name is a misnomer because the medi-
data to determine when ovulation occurs. The first involves record- cation does not have to be taken the next morning—the woman can
ing basal body temperature, the temperature taken when the woman begin the medication one to several days after having unprotected
first awakens. At the time of ovulation, her body temperature will intercourse.
increase abruptly. Simultaneously, the consistency of the mucus dis- One type of emergency contraception contains four synthetic
charge from her cervix changes from thick, dense and sticky to elastic estrogen-progesterone pills; a second type contains progesterone-
(like raw egg whites). When used correctly by trained and motivated only pills. Two pills are taken up to 72 hours after unprotected in-
couples, the method is 98% effective and free from any side effect. tercourse, and two more are taken 12 hours later. The medication
upsets the normal uterine cycle, preventing an embryo from im-
planting in the endometrium. The medication should not be used for
Emergency Contraception regular contraception. Side effects may include nausea, vomiting,
Emergency contraception, sometimes referred to as “morning- abdominal pain, fatigue, and headache. Other, more serious com-
after pills,” refers to a medication that will prevent pregnancy after plications include hypertension, cardiovascular disease, and stroke.
Genital Warts
Genital warts are caused by the human papillomaviruses (HPVs).
Many times, carriers either do not have any sign of warts or merely
have flat lesions. When present, the warts commonly are seen on the
penis and foreskin of men and near the vaginal opening in women. A
newborn can become infected while passing through the birth canal.
Individuals who are currently infected with visible growths
may have those growths removed by surgery, freezing, or burning
with lasers or acids. However, visible warts that are removed may
recur. You’ll recall (from Chapter 13) that a vaccine for the human
papillomaviruses that most commonly cause genital warts is now
available. The vaccine is an extremely important step in the preven-
tion of cancer, as well as the warts themselves. Genital warts are
associated with cancer of the cervix, as well as tumors of the vulva,
vagina, anus, and penis. Researchers believe that these viruses may
be involved in up to 95% of all cases of cancer of the cervix. Vac-
b.
cination might make such cancers a thing of the past.
Genital Herpes
Genital herpes is caused by herpes simplex virus. Type 1 usually
causes cold sores and fever blisters, while type 2 more often causes
genital herpes.
Persons usually get infected with herpes simplex virus type 2
when they are adults. Some people exhibit no symptoms; others
may experience a tingling or itching sensation before blisters
appear on the genitals (Fig. 17.17a, b). Once the blisters rupture,
they leave painful ulcers that may take as long as three weeks or
as little as five days to heal. The blisters may be accompanied by
fever, pain on urination, swollen lymph nodes in the groin, and in
women, a copious discharge. At this time, the individual has an c.
increased risk of acquiring an HIV infection. Figure 17.17 Sexually transmitted infections. (a) Herpes
After the ulcers heal, the disease is only latent, and blisters can simplex virus infection on female labia. (b) Herpes simplex virus
recur, although usually at less frequent intervals and with milder infection on the penis. (c) Treponema pallidum, the bacterium
that causes syphilis.
It is extremely important to protect yourself from getting a sexually Avoid anal-rectal intercourse (in which the penis is inserted into the
transmitted infection (STI). Some of the STIs, such as gonorrhea, rectum) because the lining of the rectum is thin and cells infected with
syphilis, and chlamydia, can be cured by taking an antibiotic. Viral HIV can easily enter the body there.
STIs, such as hepatitis, herpes, and HIV/AIDS, are incurable, though
treatment is available for HIV and herpes. In any case, it is best to Unsafe Sexual Practices Transmit STIs
prevent the passage of STIs from person to person so that you never Always use a latex condom during sexual intercourse if you don’t
need treatment at all. know for sure that your partner has been free of STIs for some time.
Be sure to follow the directions supplied by the manufacturer. Use of
Sexual Activities Transmit STIs (Fig. 17D)
a water-based spermicide containing nonoxynol-9 in addition to the
Abstain from sexual intercourse or develop a long-term monoga- condom can offer further protection because nonoxynol-9 immobi-
mous (always the same partner) sexual relationship with a partner lizes viruses and virus-infected cells.
who is free of STIs.
Avoid fellatio (kissing and insertion of the penis into a partner’s
Refrain from multiple sex partners or having relations with some- mouth) and cunnilingus (kissing and insertion of the tongue into the
one who has multiple sex partners. Think about it: if you have sex vagina) because they may be a means of transmission. The mouth and
with two other people and each of these people has sex with two gums often have cuts and sores that facilitate the entrance of infected
people and so forth, the number of people who might spread an STI cells.
dramatically increases.
Be very careful about using alcohol or any drug that may prevent
Remember that, although the prevalence of AIDS is presently you from being able to control your behavior. In a social setting where
higher among homosexuals and bisexuals, the highest rate of strangers are present, be sure to watch over your food and drinks.
increase in infection is now occurring among heterosexuals. The Date-rape drugs can be slipped into either one, and they’re usually
outermost lining of the uterus is quite thin, and it does allow infected odorless, tasteless, and invisible.
cells from a sexual partner to enter.
Be aware that having relations with an intravenous drug user is Drug Use Transmits Hepatitis and HIV (Fig. 17E)
risky because the behavior of this group risks hepatitis and an HIV Don’t ever inject drugs into your veins! Be aware that hepatitis and
infection. Recognize that anyone who already has another active STI HIV can be spread by blood-to-blood contact.
is more susceptible to an HIV infection.
Always use a new, sterile needle for injection or one that has been
Uncircumcised males are more likely to become infected with an STI cleaned in bleach if you are a drug user and can’t stop your habit.
than circumcised males because vaginal secretions can remain under Never share used needles with anyone else!
the foreskin for a long period of time.
Figure 17D Sexual activities transmit STIs. Figure 17E Sharing needles transmits STIs.
Summary
17.1 Human Life Cycle number of 46 chromosomes. along with secretions produced
The functions of the reproductive Mitosis is used in the growth of by the seminal vesicles, prostate,
system include the production and the embryo, fetus, and child. and bulbourethral glands. Sperm
transportation of gametes by the 17.2 Male Reproductive System and these secretions are called
ovaries and testes, nourishing the The primary male reproductive or- semen, or seminal fluid.
developing embryo and fetus, nour- gans are the testes. The accessory C. The external genitals of males
ishing a newborn via the production organs include the epididymis, vas are the penis, the organ of sex-
and delivery of breast milk, and sup- deferens, ejaculatory duct, seminal ual intercourse, and the scrotum,
plying the body with sex hormones. vesicles, prostate gland, bulboure- which contains the testes.
A. The life cycle of humans requires thral glands, and urethra. D. Erection is a spinal reflex that in-
two types of nuclear division: mei- A. Spermatogenesis occurs in volves the autonomic nervous
osis and mitosis. Meiosis occurs the seminiferous tubules of the system. Orgasm is a physical
in sperm production in males and testes. and emotional climax that results
ova production in females. It re- B. Sperm mature and are stored in in ejaculation of semen from the
sults in haploid cells with 23 chro- the epididymides. Sperm may penis.
mosomes. When fertilization also be stored in the vasa defer- E. Hormone regulation, involving se-
occurs, the zygote has the diploid entia before entering the urethra cretions from the hypothalamus,
Study Questions
1. Explain the process of meiosis. How is 2. Outline the path of sperm. What 3. Discuss the anatomy and physiology
a haploid cell produced from a diploid glands contribute fluids to semen? of the testes. Describe the structure of
cell? (pp. 393–395) (pp. 395–397) sperm. (pp. 395–397)
LearningTerminology
Medical Outcome Questions
Exercise
After studying this chapter, see if you can 1. orchidopexy (ŏrkĭ-dō-pĕk9sē) 6. multipara (mŭl-tĭp9ŭh-rŭh)
derive the definitions for the medical terms 2. transurethral resection of prostate 7. seminoma (sĕmĭ-nō9mŭh)
listed at right. Many of the prefixes and (TURP) (trănsyū-rē9thrăl rē-sĕk9shŭn 8. genitourinary ( jĕnĭ-tō-yū9rĭ-nār9ē)
suffixes used to create these terms can be ŭv prŏs9tāt) 9. prostatic hypertrophy (prŏs-tăt9ĭk
found throughout the chapter. For addi- 3. gonadotropic (gōnăd-ō-trōp9ĭk) hy9pĕr-trōfē)
tional help, use McGraw-Hill Connect™ at 4. gynecomastia (gīnĕ-kō-măs9tē-ŭh) 10. azoospermia (ā-zō9ō-spĕr9mē-ŭh)
www.mcgrawhillconnect.com and consult 5. hysterosalpingo-oophorectomy
Appendix B. (hĭstĕr-ō-săl-pĭng9gō-ōŏf-ŏr-ĕk9tō-mē)
T he town of Mount Airy, North Carolina, is most famous for its connections
to the fictional town of “Mayberry,” from the 1960s-era television show, The
Andy Griffith Show. Mount Airy is the birthplace of Andy Griffith, the show’s star
and namesake, and Mayberry was modeled after Mount Airy. (If you’ve never
seen The Andy Griffith Show, check it out on YouTube®.) Andy Griffith was not
the town’s only famous resident, however. There were two other Mount Airy
citizens who were famous long before The Andy Griffith Show ever began—
Chang and Eng Bunker. The Bunkers were the original “Siamese twins,” a pair
of conjoined brothers born in Siam (now modern-day Thailand) in 1811. As you’ll
discover in this chapter, conjoined twins like Chang and Eng are formed when
the developing zygote begins separating but doesn’t completely divide. Two
individuals are formed but remain connected somewhere along their bodies.
The two Bunker brothers were united at the chest by a tube of flesh, and
modern-day surgeons speculate that the twins could easily have been
separated with today’s medical knowledge and surgical procedures.
Separation was a medical impossibility then, however, and the two earned a
handsome living for a time as human oddities, giving lectures and
demonstrations throughout the United States and Europe. In 1839, they settled
on a farm in Mount Airy, then married sisters Adelaide and Sarah Yates, and
between them, fathered 21 children. The twins died within hours of each other
in 1874, at the age of 63.
Learning Outcomes After you have studied this chapter, you should be able to:
425
head
acrosome
Fertilization Membrane
Figure 18.1 Fertilization. Fertilization is accomplished in a series of steps: 1. sperm cells break aside the cells of the corona
radiata, until a single sperm is able to penetrate and adhere to the zona pellucida; 2. enzymes in the sperm’s acrosome digest the zona
pellucida; 3. sperm plasma membrane binds to the ovum plasma membrane; 4. entire sperm enters the ovum, and its nucleus is released;
5. fertilization membrane is formed, polyspermy is prevented; and 6. sperm and ovum pronuclei fuse together in a nuclear envelope.
ovum
zona pellucida
corona radiata
5. Early blastocyst
single cell =
zygote 1. Ovulation
ovary
uterine tube
2-cell 6. Implantation
stage
4-cell
3. Cleavage stage
8-cell
stage
4. Morula
Immediately after fertilization, the zygote divides repeatedly therapeutic cloning, as discussed in the Medical Focus reading
as it passes down the uterine tube to the uterus. A morula is a on page 430. Sometimes during development, either the cells of
compact ball of embryonic cells that becomes a blastocyst. The the morula separate, or the inner cell mass splits, and two em-
many cells of the blastocyst arrange themselves so that there is an bryos are present rather than one. If each of the two embryos
inner cell mass surrounded by a layer of cells, the trophoblast. is able to complete development, the two babies formed will
The trophoblast will become the chorion. The early appearance of be identical twins because they have inherited exactly the same
the chorion emphasizes the complete dependence of the develop- chromosomes. Should separation of the cell mass be incomplete,
ing embryo on this extraembryonic membrane. The inner cell mass the identical twins formed are called conjoined twins (formerly
will become the embryo. referred to as Siamese twins). Conjoined twins can be joined at
Each cell within the morula and the inner cell mass of any part of the body. Fraternal twins, who arise when two differ-
the blastocyst has the genetic capability of becoming any tis- ent ova are fertilized by two different sperm, do not have identical
sue. This recognition has recently led to a new procedure called chromosomes.
The term cloning means making exact multiple copies of genes, a cell, other sources of stem cells. Numerous exciting studies have shown that
or an organism. For example, identical twins are clones of a single zygote. the adult body has plenty of stem cells: blood, skin, liver, bone, skele-
Theoretically, cloning of human beings may someday be possible, though tal muscle, and neural stem cells have all been found. Once scientists
certainly ethically objectionable. The procedure might begin as described can effectively get adult stem cells to reproduce in cell culture, they
in Figure 18A. The person being cloned need not contribute sperm or an could be a source of tissue cells that won’t ever be rejected. It has even
egg to the process. Instead, in a process called somatic-cell nuclear been possible to coax blood stem cells and neural stem cells to become
transfer (SCNT), a 2n (diploid) nucleus from, say, a fibroblast, can be other types of human tissues in the body. Another potential source of
placed in an enucleated ovum, which then begins developing. The pre- blood stem cells is a baby’s umbilical cord, and umbilical blood can
embryo (blastocyst) would be implanted in the uterus of a surrogate now be indefinitely stored for future use. As technology improves,
mother where it would develop until birth. Although subject to envi- these types of abundant, easily obtainable stem cells might just hold
ronmental influences, the clone would be expected to closely resemble the promise of a cure for many human diseases and disorders.
its “parent.” (For example, Dolly the sheep, cloned in 1996, was the
first mammal ever to be produced through SCNT.)
Therapeutic cloning is not the same as cloning a human being skin fibroblast
because the cells of the created pre-embryo are never introduced into the
enucleated ovum
uterus. Instead, they are separated and treated to become particular tis- patient
sues, which can then be used to treat the patient. The separated cells of a
pre-embryo are called stem cells because they divide repeatedly and can
become various tissues, as shown in Figure 18A. Theoretically, tissues
resulting from this procedure will not be subject to rejection by the
patient because they will bear the same surface molecules as the patient’s
cells. However, it’s important to remember that an ovum contains mito- cell fusion
chondrial DNA (mtDNA) from the mother. Researchers are uncertain
what, if any, effect mtDNA could have on the development of rejection.
Researchers hope that one day therapeutic clone cells may provide
insulin-secreting cells for diabetics, nerve cells for stroke patients or those mitosis
with Parkinson’s disease, cardiac cells for those with heart disease, and so
forth. However, so far therapeutic cloning is experimental and has not
been perfected. To date, the research is extremely expensive to carry out morula
and has a very high failure rate. Further, questions remain about what the
new cells will do once implanted in the person’s body—will they spread mitosis
like cancer cells do? Moreover, it is important to recognize that ethical inner cell
concerns about therapeutic cloning will always remain—after all, any mass
pre-embryo is potentially an entire, living human being.
Anticipating intense interest in therapeutic cloning, the U.S.
National Academy of Sciences proposed strict new guidelines for fed-
blastocyst
erally funded research in 2005. As a result, Embryonic Stem Cell
Research Oversight, or ESCRO, committees were created to approve
any research before it could begin. An ESCRO committee review is
embryonic stem cells
carried out in addition to the current review always required by an
Institutional Review Board, or IRB. ESCRO committees include bio-
ethicists and legal experts, as well as members of the general public.
ESCRO rules require that prior to beginning any research, cultured
stem cells
informed consent from the donors of ova or sperm must be obtained.
Further, stem cells created for therapeutic cloning must never be used
for reproductive purposes. Additional restrictions require that the Figure 18A Therapeutic
embryos created cannot be grown in culture for longer than 14 days. cloning. By placing a
At that point, the primitive streak of the developing nervous system patient’s cell nucleus into
tissues
begins to form. The Academy formed a national agency charged with an enucleated ovum, stem
cells can be obtained. blood muscle nervous
regularly reviewing all guidelines on stem cell research, and these
reviews were conducted in 2008 and 2010. Then, embryonic stem
cells are grown to form
Problems with rejection of embryonic stem cells, as well as the
tissues for transplant. Transplantation in Patient
ethical issues surrounding their use, have led researchers to pursue
amniotic cavity
notochord
ectoderm
yolk sac
ectoderm endoderm
mesoderm
Figure 18.4 Embryonic germ layers. An embryo has three primary germ layers: ectoderm, mesoderm, and endoderm. Organs and
tissues can be traced back to a particular germ layer as indicated in this illustration.
Placenta eighth week when they begin to disappear, except in one area. These
The placenta is shaped like a pancake, measuring 15 to 20 cm in villi are surrounded by maternal blood, and it is here that exchanges
diameter and 2.5 cm thick. The placenta is normally fully formed of materials take place across the placental membrane. The placental
and functional by the end of the embryonic period and before the membrane consists of the epithelial wall of an embryonic capillary
fetal period begins. The placenta is expelled as the afterbirth and the epithelial wall of a chorionic villus. Maternal blood rarely
following the birth of an infant. mingles with fetal blood. Instead, oxygen and nutrient molecules,
The placenta has two portions, a fetal portion composed of such as glucose and amino acids, diffuse from maternal blood across
chorionic tissue and a maternal portion composed of uterine tissue. the placental membrane into fetal blood, and carbon dioxide and other
Chorionic villi cover the entire surface of the chorion until about the wastes, such as urea, diffuse out of fetal blood into maternal blood.
Figure 18.5 Embryonic development within the uterus. (a) Three weeks after fertilization. (b) Five weeks after fertilization,
amnion and chorion are present, and the uterus is about the size of a hen’s egg. (c) Two months after fertilization, the placenta and
umbilical cord are well formed.
brain tail
brain
optic
vesicle
optic
vesicle
pharyngeal
tail arch
pharyngeal
arch heart
region of liver
heart, liver
umbilical
vessel
umbilical
vessel
somite
gastrointestinal tract limb bud
a. b.
Figure 18.6 Human embryo at beginning of fifth week. (a) Scanning electron micrograph. (b) The embryo is curled so that the head
touches the region of the heart and liver. The organs of the gastrointestinal tract are forming, and the arms and the legs develop from the
bulges called limb buds. The tail is an evolutionary remnant; its bones regress and become those of the coccyx (tailbone).
Wolffian duct
Müllerian duct
probladder
kidney
cloaca
limb bud
weeks 5–6
no Y chromosome Y chromosome
urogenital groove
ovaries testes
Müllerian
duct forming epididymis 6 weeks
the uterine Wolffian Müllerian
tube duct duct
(degenerating) (degenerating)
fused Müllerian urinary Y chromosome no Y chromosome
ducts forming Wolffian duct bladder
the uterus urinary forming the
bladder ductus deferens glans
(moved aside) urogenital
seminal vesicle
groove
Figure 18.9 Male and female organs. (a) Development of gonads and ducts. (b) Development of external genitals.
urethra
urinary bladder
vagina
cervix
placenta ruptured
rectum amniotic
sac
placenta
uterus
placenta
umbilical
cord
c. Second stage of birth: baby emerges d. Third stage of birth: afterbirth is expelled
Figure 18.10 Three stages of parturition (birth). (a) Position of fetus just before birth begins. (b) Dilation of cervix. (c) Birth of baby.
(d) Expulsion of afterbirth.
In Memoriam: Brandon Nelson, 1982–1983 features persist in the newborn, oxygen-rich blood will mix
Each and every day in the United States, approximately 1,300 babies with oxygen-poor blood. Blood circulation will be impaired,
will be born too soon. Premature birth is defined as birth prior to perhaps leading to the delivery of a “blue baby”—that is, a
37 weeks gestation (normal gestation is approximately 40 weeks). baby with cyanosis, a bluish cast to the skin. Heart failure can
Many other babies, although full-term, have a low birth weight (less also result from these conditions.
than 5.5 pounds at birth). These babies face weeks to months in the Risk for permanent disability Many premies grow up to be normal
neonatal intensive care unit, or NICU. Fortunately, advances in the and healthy, but many others face permanent disability. Devel-
care of these tiniest patients allow most of them to continue to grow opmental delays, cerebral palsy, learning disorders, chronic
and develop while slowly gaining weight. Most eventually go home. lung disease, blindness, and deafness are all potential conse-
However, “premies” and term babies with low birth weight face many quences of premature birth. Further, pediatricians estimate that
serious challenges to their survival: fully half of all neurological disabilities in children are related
to premature birth.
Respiratory distress syndrome (hyaline membrane disease) The lungs
do not produce enough of the chemical surfactant that helps the Why do women deliver prematurely? Obstetricians (physicians
alveoli stay open (see Chapter 14, page 324). Therefore, the who specialize in the treatment of women during and after pregnancy)
lungs tend to collapse, instead of expanding to be filled with air. have come up with four general causes for preterm labor and delivery.
Retinopathy of prematurity The high level of oxygen needed to en- The placenta may be disrupted by a bacterial infection; this triggers
sure adequate gas exchange by the immature lungs can lead to uterine contractions. Bleeding from the placenta or from the uterus
proliferation of blood vessels within the eyes, with ensuing itself may trigger labor. The uterus may be stretched excessively, as
blindness. often occurs in multiple births. Finally, maternal or fetal stress may
Intracranial hemorrhage The delicate blood vessels in the brain are trigger a hormone cascade that leads to uterine contraction and pre-
apt to break, causing swelling and inflammation of the brain. If term delivery. Pregnant women who have already had a previous pre-
not fatal, this can lead to brain damage. term delivery are known to be at risk for subsequent preterm delivery,
Jaundice The immature liver fails to excrete the waste product bili- as are women pregnant with twins, triplets, or more. Structural abnor-
rubin, which instead builds up in the blood, possibly causing malities of the uterus or the cervix may also lead to delivery of a
brain damage. premature baby.
Infections The level of antibodies in the body is low, and the various Unfortunately, despite increased research and improvements in
medical procedures performed could possibly introduce patho- medical care, the rate of premature birth has increased by 31% in the
gens. Also, bowel infection is common, along with perforation, past 20 years. Obviously, more needs to be done to prevent premature
bleeding, and shock. birth, and you can read more about it in the Medical Focus on
Circulatory disorders Fetal circulation, discussed in Chapter 12, has pages 440–441. The March of Dimes supports educational efforts and
two features: (1) the oval opening between the atria, and (2) the research into the causes of birth defects and prematurity. More infor-
arterial duct that allows blood to bypass the lungs. If these mation can be obtained at www.marchofdimes.com.
decreases uterine motility by relaxing smooth muscle, including sphincter and reflux of stomach contents into the esophagus. Con-
the smooth muscle in the walls of arteries. The arteries expand, and stipation is caused by a decrease in intestinal tract motility.
this leads to a low blood pressure. Hypotension causes the kidneys Pregnancy results in respiratory system changes caused both
to release their enzyme, renin. The renin-angiotensin-aldosterone by progesterone and by the increasing size of the uterus. Under the
mechanism is thus activated, and is promoted by estrogen. Aldo- influence of progesterone, the bronchial and bronchiolar smooth
sterone activity promotes sodium and water retention, and blood muscle relaxes. The brain is signaled to lower CO2,which it does
volume increases until it reaches its peak sometime during weeks by increasing respiratory rate and depth. Compared to nonpreg-
28–32 of pregnancy. Altogether, blood volume increases from nant values, the maternal blood oxygen level changes little, but
5 liters to 7 liters—a 40% rise. An increase in the number of red blood carbon dioxide levels fall by 20%, creating a concentration
blood cells follows. With the rise in blood volume, cardiac output gradient that favors the flow of carbon dioxide from fetal blood to
increases by 20–30%. Blood flow to the kidneys, placenta, skin, maternal blood at the placenta. The increasing size of the uterus
and breasts rises significantly. Smooth muscle relaxation also ex- from a nonpregnant weight of 60–80 g to 900–1,200 g means that
plains the common gastrointestinal effects of pregnancy. The heart- it will occupy most of the abdominal cavity, reaching nearly to
burn experienced by many is due to relaxation of the esophageal the xiphoid process of the sternum. The pregnant uterus not only
Before the nursery room gets painted pink or blue, before the baby regis- smoke are more likely to have erectile dysfunction than nonsmokers.
try is completed at the department store, before deciding whether the Further, it will later be essential for both the pregnant mother and the
baby gets named after Great-Aunt Adelaide or Grandma Gertrude, a fetus to be in a smoke-free environment at all times.
couple that has decided to start (or add to) a family must take precautions Because the placenta functions as a filter, if mom smokes or
to prevent congenital, or birth, defects. Some birth defects are encounters secondhand smoke, her baby “smokes,” too. Cleft lip/cleft
unavoidable—those caused by chromosomal or genetic abnormalities, palate may occur because of exposure to toxins in cigarette smoke.
for example. Tragically, however, many other birth defects are com- Children of smoking mothers are more likely to be stillborn, or die
pletely preventable. shortly after birth. Death from sudden infant death syndrome (SIDS—
For decades, the placenta was believed to be an effective barrier unexplained death of an otherwise healthy baby) is more common in
between mother and fetus, but continuing research has shown instead babies of smoking mothers. The occurrence of preterm babies with
that the placenta is really a filter through which many substances can low birth weight is doubled for women who smoke.
enter the baby’s bloodstream from the mother’s circulation. Thus, Alcohol easily crosses the placenta, and there is no safe dosage
almost anything that mom eats, drinks, smokes, or injects—good and during pregnancy. Even one drink a day appears to increase the chances
bad—is potentially capable of winding up in the baby’s body. of miscarriage. The more alcohol consumed, the greater the baby’s
Chemicals, bacteria, viruses, parasites, antibodies from the mother’s chance of physical abnormalities. Fetal alcohol syndrome (FAS) is
immune system (both harmful and beneficial) can all act as the term given to the collection of physical, mental, and behavioral
teratogens—agents capable of causing birth defects. abnormalities seen in babies born to heavy drinkers. FAS babies have
Ideally, preventing birth defects, is a process that should begin decreased weight, height, and head size, with malformation of the
before a woman ever becomes pregnant. At a complete physical exam head and face. Later, developmental delay is common, as are numer-
before pregnancy, she can receive any necessary immunization boost- ous other physical malformations. Babies born to heavy drinkers are
ers, or “catch up” with immunizations she may have missed as a child apt to undergo an extremely painful withdrawal, called delirium
(see pages 309–310). It is especially important to immunize against tremens, after birth—shaking, vomiting, and extreme irritability.
rubella (German measles) because it can cause blindness, deafness, Any use of recreational drugs must end before attempting to
mental retardation, heart malformations, and other serious problems conceive, because all will decrease a man’s sperm count. Certainly,
in an unborn child. Antibiotic treatment can cure bacterial STIs (syph- illegal drugs such as marijuana, cocaine, and heroin are teratogens
ilis, gonorrhea, chlamydia, etc.) and prevent serious harm to the that must be completely avoided during pregnancy. All increase the
embryo. Although there are no cures for viral STIs, it is still important probability of pregnancy complications, including stillbirth. In par-
to know if a woman is infected. As you know, HIV can cross the pla- ticular, cocaine use causes severe fluctuations in a mother’s blood
centa, but highly active anti-retroviral therapy (HAART) can often pressure that temporarily deprive the developing fetus’s brain of oxy-
prevent fetal infection (see pages 307–308). Health-care providers gen. Approximately 60% of drug-affected babies are cocaine babies;
will also recommend prenatal vitamin/mineral supplements with high if they survive, they can have visual problems, lack coordination, and
levels of vitamin B12 and folate, before and after conception, to are often developmentally delayed.
minimize the risk of neural tube defects such as spina bifida. Once pregnancy occurs, prenatal medical care and good health
Couples trying to conceive should also adapt their lifestyle, if habits must continue. A healthy pregnancy diet should contain mod-
necessary. If either or both partners smoke, there will never be a more erate increases in calories and protein to meet the demands of both
perfect time to quit (see pages 333–334 for helpful tips). Males who fetus and mother. The pregnant woman of normal weight should
pushes the intestines, liver, stomach, and diaphragm superiorly, but makes cells resistant to insulin, and the result can be gestational
it also widens the thoracic cavity. As a result, a pregnant woman (pregnancy-induced) diabetes. Some of the integumentary
cannot breathe quite as deeply, nor exhale as forcefully. changes observed during pregnancy are also due to placental hor-
The enlargement of the uterus does result in additional prob- mones. Striae gravidarum, commonly called “stretch marks,”
lems. In the pelvic cavity, compression of the ureters and urinary typically form over the abdomen and lower breasts in response to
bladder can result in stress incontinence, during which the preg- increased steroid hormone levels rather than stretching of the skin.
nant woman involuntarily urinates. Compression of the inferior Melanocyte activity also increases during pregnancy. Darkening of
vena cava, especially when lying down, decreases venous return, the areolae, skin in the line from the navel to the pubis, areas of the
and the result is edema and varicose veins. face and neck, and vulva is common.
Aside from the steroid hormones progesterone and estrogen, Changes in breast anatomy and the development of lactation
the placenta also produces some peptide hormones. One of these are discussed in Chapter 17, pages 407 and 409.
Content CHECK-UP!
7. Oxytocin is an essential hormone both for labor and delivery 9. Which of the following is an effect of placental estrogen?
and the months after birth as well. What are its functions dur- a. reduced uterine motility
ing this entire time? What are the consequences if oxytocin
b. relaxation of smooth muscle
production does not occur?
c. increased insulin resistance
8. Effacement is the technical term for:
d. increased uterine blood flow
a. leakage of amniotic fluid.
Answers in Appendix A.
b. false labor contractions.
c. the process of gradually stretching the cervix until it slowly
disappears.
d. loss of the mucous plug that blocked the cervical canal.
Summary
18.1 Fertilization B. The extraembryonic mem- D. The gonads start to develop during
A. A sperm consists of a head, a branes, placenta, and umbilical the seventh week. Testosterone
middle piece, and a flagellum tail. cord allow humans to develop induces the gonads to form into
The ovum is surrounded by a within the uterus. These struc- testes; without testosterone, they
non-living matrix called the zona tures protect the embryo and al- will form into ovaries.
pellucida and an outermost low it to exchange wastes, 18.3 Birth
cellular corona radiata. nutrients, and oxygen with the A. During stage 1 of parturition, the
B. During fertilization, the sperm’s mother’s blood. cervix effaces and dilates.
acrosomal enzymes help to di- C. At the end of the embryonic pe- B. During stage 2, the child is born.
gest the layers around the ovum riod, all organ systems are es- C. During stage 3, the afterbirth is
so a single sperm can penetrate tablished, and there is a mature expelled.
it. There, the sperm nucleus and functioning placenta. Fetal D. During pregnancy, the mother’s
fuses with the ovum nucleus to development extends from the uterus enlarges greatly, resulting
create a zygote with a unique set third through the ninth months. in weight gain, standing and
of chromosomes. Following suc- During the third and fourth walking difficulties, and general
cessful implantation by the em- months, the skeleton is becom- discomfort. It comes to occupy
bryo, a positive blood or urine ing ossified and the sex of the most of the abdominal cavity
test for HCG will confirm the fetus becomes distinguishable. with resultant annoyances such
pregnancy. During the fifth through ninth as incontinence. Many of the
18.2 Development months, the fetus continues to complaints of pregnancy, such as
A. Cleavage of the zygote and early grow and to gain weight. Babies constipation, heartburn,
embryo forms a ball of cells that born after six or seven months darkening of certain skin areas,
then differentiate. The first organ may survive, but full-term ba- and diabetes of pregnancy are
system to appear is the nervous bies have a better chance of due to the presence of placental
system. survival. hormones.
A s you begin to study the topic of human genetics in this chapter, you might
be interested to know that genetic chance was, in part, responsible for
changing European history. In the early 1900s, the last Russian monarch, Tsar
Nicholas Romanov, and his wife, Tsarina Alexandra, had four daughters but were
desperate for a male heir for the throne. When their fifth child, crown prince
Alexei, was born in 1904, the couple was heartbroken to discover that their son
suffered from hemophilia, a sex-linked genetic disorder that causes uncontrolled
bleeding in affected boys. When physicians of the time couldn’t help their son,
the Romanovs turned to Grigory Rasputin, a Russian mystic often called the
“mad monk.” Historians aren’t sure how Rasputin did it, but he was able to
alleviate Alexei’s suffering. In so doing, Rasputin won the trust of the monarchs,
and gained great influence over their decisions. On Rasputin’s advice, Tsar
Nicholas took control of the Russian army from his generals during World War I,
a decision that scholars agree helped to contribute to Russia’s defeat. Would
Nicholas have been a more effective ruler (and might Europe look different
today?) if his only son hadn’t suffered from a genetic disorder? No one will ever
know. Nicholas abdicated the throne on March 9, 1917, setting the stage for the
Russian revolution, and the entire Romanov family was assassinated in July 1918.
Learning Outcomes After you have studied this chapter, you should be able to:
Focus on Forensics
The Innocence Project
445
tiny sample of chorionic cells is withdrawn by suction. The cells do nucleus of a cell that is about to divide (the chromosomes are more
not have to be cultured, and karyotyping can be done immediately. visible then), so that a picture of the chromosomes is obtained. The
However, this sampling procedure does not gather any amniotic picture may be entered into a computer, and the chromosomes elec-
fluid, so the biochemical tests done on the amniotic fluid follow- tronically arranged by pairs (Fig. 19.1c). The resulting display of
ing amniocentesis are not possible. CVS also carries a greater risk chromosomes is the karyotype. Figure 19.1d,e compares a normal
of spontaneous abortion than amniocentesis—0.8% compared to karyotype with that of a person who has Down syndrome, the most
0.3%. Further, CVS has been suggested as the cause behind certain common autosomal abnormality.
limb and facial congenital abnormalities. The advantage of CVS is
that the results of karyotyping are available at an earlier date. Nondisjunction
An abnormal chromosomal makeup in an individual can be due
Preparing the Karyotype to nondisjunction. Nondisjunction occurs during meiosis I when
After a sample of cells has been obtained, the cells are stimulated to both members of a homologous pair go into the same daughter cell
divide in a culture medium. A chemical is used to stop mitosis dur- or during meiosis II when the sister chromatids fail to separate and
ing metaphase when chromosomes are the most highly compacted both daughter chromosomes go into the same gamete (Fig. 19.2). If
and condensed. The cells are then spread on a microscope slide an ovum with 24 chromosomes is fertilized by a normal sperm cell
and dried. Stains are applied to the slides, and the cells are photo- with 23 chromosomes, the zygote formed has a trisomy: One type
graphed. Staining produces dark and light cross-bands of varying of chromosome is present in three copies instead of the normal two,
widths, and these can be used in addition to size and shape to and the total chromosome count is 47 instead of the normal 46.
help pair up the chromosomes. Today, a computer may be used to Conversely, if an ovum with 22 chromosomes is fertilized with a
arrange the chromosomes in pairs. It is possible to photograph the normal sperm, the zygote formed carries a monosomy: One type
nondisjunction
48 chromatids 44 chromatids
in 24 pairs in 22 pairs
meiosis II
X XX XY
and prostate gland are underdeveloped, and the individual has no
facial hair. Also, some breast development may occur (Fig. 19.4b).
Nondisjunction also occurs with regard to the sex chromo- Affected individuals have large hands and feet and very long arms
somes. Ova or sperm with too many or too few sex chromosomes and legs. They may have developmental delays, particularly if they
can occur. Therefore, nondisjunction accounts for the birth of indi- inherit more than two X chromosomes.
viduals with too few or too many sex chromosomes. A poly-X female has more than two X chromosomes. Females
with three X chromosomes have no distinctive physical appearance,
aside from a tendency to be tall and thin. Some exhibit delayed
Too Many/Too Few Sex Chromosomes motor and language development, though most are normal. Some
From birth, an XO individual with Turner syndrome has only one may have menstrual difficulties, but many menstruate regularly
sex chromosome, an X; the O signifies the absence of a second and are fertile. Their children usually have a normal karyotype.
sex chromosome. Turner females are short, with a broad chest Females with more than three X chromosomes occur rarely.
and a webbed neck. The ovaries, uterine tubes, and uterus are Unlike XXX females, XXXX females are usually tall and severely
very small and nonfunctional. Turner females do not undergo pu- developmentally delayed. Various physical abnormalities are seen,
berty or menstruate, and their breasts do not develop (Fig. 19.4a). but they may menstruate normally.
They are usually of normal intelligence and can lead fairly normal XYY males with Jacobs syndrome can only result from nondis-
lives. Though Turner females have occasionally given birth follow- junction during spermatogenesis. This is because only males have a
ing in vitro fertilization using donor ova, there are significant risks Y chromosome. Affected males are usually taller than average, suffer
for both the mother and baby. Pregnant Turner syndrome women from persistent acne, and tend to have speech and reading problems.
are at high risk of developing pregnancy-related high blood pres- At one time, it was suggested that these men were likely to be crimi-
sure, a condition called pre-eclampsia. If untreated, pre-eclampsia nally aggressive, but it has since been shown that the incidence of
can lead to heart attack and stroke. Further, almost 40% of babies such behavior among them may be no greater than among XY males.
of Turner mothers are born prematurely. Notice that there are no YO males. This shows that at least one
A male with Klinefelter syndrome has two or more X chro- X chromosome is needed for survival. However, XXY individuals
mosomes in addition to a Y chromosome, and is sterile. The testes are males, not females.
Inheritance of Genes on
Autosomal Chromosomes
zygote zygote An individual normally has two alleles for an
autosomal trait. Just as one member of each
pair of chromosomes is inherited from each
growth and development growth and development parent, so too is one of each pair of alleles inherited from each par-
ent. If the two alleles are identical, the pair is termed homozygous;
if not, the pair is heterozygous.
The term genotype refers to the genes of the individual.
Figure 19.5 shows four possible fertilizations and the resulting
genotype of the individual for earlobe attachment. In the first in-
stance, the chromosomes of both the sperm and the ovum carry an
E. Consequently, the zygote and subsequent individual have the al-
leles EE, which can be called a homozygous dominant genotype.
A person with genotype EE obviously has unattached earlobes. The
physical appearance of the individual—in this case, unattached
earlobes—is called the phenotype.
In the second fertilization, the zygote has received two reces-
unattached earlobe attached earlobe unattached earlobe
sive alleles (ee), and the genotype is called homozygous recessive.
An individual with this genotype has the recessive phenotype,
Figure 19.5 Genetic inheritance. Individuals inherit a minimum which is attached earlobes. In both the third and fourth examples
of two alleles for every characteristic of their anatomy and physiol- of fertilization, the resulting individual has the alleles Ee, which
ogy. The inheritance of a single dominant allele (E) causes an indi- is a heterozygous genotype. A heterozygote shows the dominant
vidual to have unattached earlobes; two recessive alleles (ee) characteristic; therefore, the phenotype of this individual is unat-
cause an individual to have attached earlobes. Notice that each in- tached earlobes.
dividual receives one allele from the father (by way of a sperm) and
How many dominant alleles does an individual need to in-
one allele from the mother (by way of an ovum).
herit to have a dominant phenotype? These examples show that a
Sex-Linked Inheritance
The sex chromosomes contain genes just as the autosomal chromo-
somes do. Some of these genes determine whether the individual It’s a girl: XB XB It’s a girl: XB Xb It’s a boy: XB Y It’s a boy: Xb Y
is a male or a female. Investigators have now discovered a series Normal, and not a carrier Normal, but a carrier
a. for color blindness for color blindness
Normal COLOR BLIND
Examples of dominantly Examples of recessive inherited Examples of X-linked disorders Examples of multifactorial
inherited disorders include: disorders include: include: inheritance include:
∙ Neurofibromatosis—benign ∙ Cystic fibrosis—disorder ∙ Agammaglobulinemia—lack ∙ Cleft lip and/or palate
tumors in skin or deeper affecting function of mucous of immunity to infections ∙ Clubfoot
∙ Achondroplasia—a form of and sweat glands ∙ Color blindness—inability to ∙ Congenital dislocation of the
dwarfism ∙ Galactosemia—inability to distinguish certain colors hip
∙ Chronic simple glaucoma metabolize milk sugar ∙ Hemophilia (some forms)— ∙ Spina bifida—open spine
(some forms)—a major ∙ Phenylketonuria—essential defect in blood-clotting
cause of blindness if liver enzyme deficiency mechanisms ∙ Hydrocephalus (with spina
untreated bifida)—water on the brain
∙ Sickle-cell disease—blood ∙ Muscular dystrophy (some
∙ Huntington disease— disorder primarily affecting forms)—progressive wasting ∙ Pyloric stenosis—narrowed or
progressive nervous system blacks of muscles obstructed opening from
degeneration stomach into small intestine
∙ Thalassemia—blood disorder ∙ Spinal ataxia (some forms)—
∙ Familial primarily affecting persons of spinal cord degeneration ∙ Breast cancer
hypercholesterolemia— Mediterranean ancestry ∙ Diabetes mellitus
high blood cholesterol levels, ∙ Tay-Sachs disease—lysosomal ∙ Coronary artery disease
propensity to heart disease storage disease leading to
∙ Polydactyly—extra fingers or nervous system destruction
toes
Source: Data from the National Foundation/March of Dimes.
Figure 19.8 Inheritance pattern for CF, an autosomal reces- Previously, you studied the structure of DNA and how it replicates
sive disorder. (a) The figures below the parents show four possible and carries out protein synthesis. DNA technology includes our
combinations of inherited alleles. Therefore, each offspring has a ability to work directly with DNA to determine the relatedness of
25% chance of inheriting two recessive alleles and having CF. individuals, to assist forensics in determining whether a person
(b) A sample pedigree for carrier parents and their children. Note has committed a crime, and to develop new treatments for human
that Sue and Rod are carriers like their parents Joe and Mary, and illnesses, called gene therapy.
Tina is affected with CF.
Gene Therapy
Gene therapy is the insertion of genetic material into human cells
for the treatment of a disorder. It includes procedures that give
abnormal genes are inherited. The inheritance of these condi- a patient healthy genes to make up for faulty genes and also in-
tions, listed in the “Multiple Genes” column in Table 19.2, is cludes the use of genes to treat various other human illnesses, such
complex. as cancer and cardiovascular disease. Currently, approximately
Often parents want to improve their chances of having a 1,700 patients are enrolled in over 300 approved gene therapy trials
child who is free of a particular genetic disorder that runs in in the United States.
their families. As you have learned, testing of cell-free fetal How can a molecule as large as a gene be introduced, intact,
DNA in the maternal bloodstream can be followed by chorionic into a cell? The most common approach used by scientists is to
villus sampling or amniocentesis. The Medical Focus reading employ a vector—a carrier whose job is to transport the DNA
on page 455 describes techniques for preimplantation genetic directly into the cell. Viruses are nature’s own vectors because they
diagnosis (PGD). Using PGD, the ovum can be analyzed to ensure replicate themselves by inserting their own genetic material into a
that it does not carry an abnormal allele prior to in vitro fertil- host cell. Scientists studying gene therapy techniques have adapted
ization, or the embryo itself is tested for genetic defects before viruses to function as vectors. The viruses are first modified: Viral
being introduced into its mother’s uterus. In the future, it might genetic material is removed or altered so that it does not cause
be possible to use gene therapy to cure any genetic defects found disease, and human genes are inserted into the virus instead. Next,
in an ovum or embryo. the virus is allowed to infect human tissue, where it inserts the
—Continued
not be able to implant. Thus, couples who elect to have PGD have a presumed to be disease-free. Likewise, if the polar body sister
lower chance of having a viable embryo. Moreover, experts in medi- chromatids contain the Huntington’s disease dominant gene in a
cal ethics continue to question the use of all forms of PGD. Pointing woman with a family history of that disease, the secondary oocyte has
to the fact that each cell in an eight-cell embryo is totipotent, they the normal recessive gene. In either case, normal secondary oocytes
argue that the single cell used for testing is a potential human being are then fertilized and implanted into the woman’s uterus, and
that is destroyed by the testing process. Likewise, defective embryos defective secondary oocytes are destroyed. (But the technique is not
are potential human beings that will ultimately be destroyed. Further, perfect; there’s a slight chance that crossing-over during prophase I
it’s known that many genetic disorders don’t appear in the affected may have put the defective gene into the secondary oocyte’s chromo-
individual before the third or fourth decade of life. It’s feasible that a somes. See pages 393–395 to review crossing-over.)
cure for the disorder could be found during that time period. Finally, Regardless of the technique that is used, ethical issues about
medical ethicists stress that although children with genetic or chromo- PGD continue to surface. In several instances worldwide, families
somal abnormalities may have medical issues that must be overcome, with a child suffering from a serious blood disorder (leukemia or
their lives can have tremendous meaning and value to their families genetic anemias) have already used PGD to create a “savior baby”—a
and to society. Moral philosophers contend that ending a life shortly second child free of the genetic disorder whose umbilical cord blood
after conception is an act whose morality must be seriously was then transfused into the ill sibling. This practice creates further
questioned. concern that PGD could be used to create babies for their “spare
A second method of PGD, called polar body biopsy (PBB), parts.” Perhaps most disturbing is the notion that PGD could eventu-
avoids the ethical issues surrounding embryonic testing, but its use- ally be used to select only for embryos with a couple’s desired charac-
fulness is limited to detecting the presence of defective genes in a teristics: gender, intelligence, physical appearance, or athletic ability.
woman who is heterozygous for a particular single gene disease (see PGD is already being used by couples who want a male child to select
Table 19.2). PBB involves removal and testing of the chromosomes in only male embryos for implantation—and any female embryos are
the polar body that lies alongside the secondary oocyte. As you know subsequently destroyed. In societies worldwide where male children
(from Chapter 18), the polar body is like a “garbage can,” because it are valued more than females, practitioners of PGD find a very lucra-
contains 23 pairs of sister chromatids that are discarded after meiosis I. tive market for their skills.
The remaining 23 pairs remain in the secondary oocyte. For example, The debate will undoubtedly continue over the uses of this type
consider a woman who is heterozygous for Tay-Sachs disease. If her of technology, and others like it that will develop in the future. It is
polar body chromosome pair has the Tay-Sachs recessive gene, the important that all of us are well informed and understand the scien-
secondary oocyte chromosome pair has the dominant gene and is tific issues so that we can make informed decisions.
healthy human genes into tissue cells. Four classes of viruses have Among the many gene therapy trials, one is for the treatment
been employed in gene therapy research: (1) retroviruses, like the of familial hypercholesterolemia, a condition that develops when
virus that causes AIDS; (2) adenoviruses, which are a form of cold liver cells lack a receptor for removing cholesterol from the blood.
virus; (3) herpes viruses, which cause cold sores on the mouth; The high levels of blood cholesterol make the patient subject to
and (4) the most commonly used virus vector, the adeno-associated fatal heart attacks at a young age. In a newly developed procedure,
virus, a very small virus that can have all of its own genetic ma- a small portion of the liver is surgically excised and infected with
terial removed and still be capable of infecting cells. Scientists a virus containing a normal gene for the receptor. Several patients
have seen some early successes in the treatment of several immune have experienced lowered serum cholesterol levels following this
system deficiency diseases, as well as inherited diseases affecting procedure.
metabolism. Cystic fibrosis patients have an abnormal gene for a trans-
Other mechanisms to insert genes into cells are also being membrane carrier of the chloride ion. Patients often die due to
investigated. One way is to introduce DNA directly into cells. A numerous infections of the respiratory tract. In a newly developed
second mechanism involves attaching the gene to a liposome. Li- procedure, liposomes have been coated with the gene needed to
posomes are microscopic vesicles that form spontaneously when cure cystic fibrosis. The liposomes have then been delivered to the
lipoproteins are put into a solution. Still other scientists attach lower respiratory tract.
the DNA to molecules that have specific receptors on the cell Genes are also being used to treat medical conditions other
membrane, then allowing the cell to incorporate the DNA by than the known genetic disorders. VEGF (vascular endothelial
phagocytosis. growth factor) can cause the growth of blood vessels. The gene that
Consider for a moment that you’re a young woman who is going the mother’s bloodstream? Could it cause an immune response, or even
blind, and the doctors tell you that you’ve inherited a condition called cancer? And the most fundamentally important question of all: is there
Leber hereditary optic neuropathy. After researching the condition on any guarantee that the resulting child will be healthy and normal?
the Internet1, you discover that this disease is not inherited in the way Other countries, including the United States, are carefully con-
you might have expected (by mutation of the chromosomes in your sidering Britain’s decision to permit mitochondrial donation. Bioethi-
cells’ nuclei). Rather, this mutation took place in the DNA of your cists everywhere fear that mitochondrial donation is unethical for all
mitochondria. As you know from Chapter 18, human mitochondria individuals involved. The ovum donor and the mother must take hor-
come from the ovum that formed the zygote, not the sperm. That mones to make multiple ova develop within their ovaries and then
means your children’s mitochondria will all have this mutation, undergo laparoscopic surgery to have the ova removed. Both the hor-
though they may or may not display disease symptoms. But what if mones and the surgery involve serious potential (and potentially fatal)
you first replace your mitochondria with a donor’s healthy ones? health risks. Should an ovum donor be subject to these risks, and
That’s the basic premise behind a technique called mitochondrial should she be paid? Will her DNA contribution show up in the child’s
donation, which was approved for human experimentation in the physical, intellectual, or psychological makeup? Does she have any
United Kingdom in February 2015. There are two methods for the legal rights at all regarding the child created from her ovum? Further-
procedure. In maternal spindle transfer, the pronucleus in an ovum more, should a healthy embryo be destroyed in pronuclear transfer so
donated by a healthy woman (i.e., one who is free of mitochondrial that scientists can create the new “hybrid” one? What if the resulting
disease) is destroyed and replaced with the pronucleus from the moth- child has a physical or intellectual disability or a shortened life span?
er’s own defective ovum. This reengineered ovum is then fertilized Even more concerning is a new technology called clustered regu-
with the husband’s sperm. With the second method, pronuclear trans- larly interspaced short palindromic repeat technology (CRISPR). Using
fer, two embryos are first created by fertilizing both the donor ovum this technique, scientists can change the actual chromosomes of a cell by
and the mother’s ovum with the father’s sperm. The nucleus of the adding or deleting snippets of DNA. If the process is only used to correct
healthy donor embryo is removed and destroyed, then replaced with mutations in somatic stem cells (the body’s own stem cells, which pro-
the nucleus from the mother’s embryo. In both techniques, the result- duce muscle cells, nerve cells, etc.), it holds the promise of correcting and
ing embryos are theoretically free of the mother’s defective mito- curing genetic disorders such as cystic fibrosis or Tay-Sachs disease.
chondria and can then be introduced into the mother’s uterus. If the Altered somatic cell chromosomes aren’t passed to a person’s children.
embryo implants and is carried to term, the baby will have three sets But what if the procedure is used to alter the chromosomes in embryos?
of DNA: mitochondrial DNA from the ovum donor and nuclear DNA If the embryo implants and completes development, its transformed
from the mother and father. Though neither of these techniques has DNA will theoretically pass to future generations. In theory, this means
been attempted in humans, experimentation in mice and monkeys has that the next generation’s future children could inherit undesirable traits,
successfully produced offspring that seem healthy and disease-free. such as a tendency for uncontrolled rage. Moreover, what if the technol-
Though mitochondrial donation seems an “easy” cure for a number ogy is used to attempt to create a “perfect race?” Novels such as Aldous
of serious illnesses, the entire process still has serious short-term and Huxley’s Brave New World explore the fictional consequences of such a
long-term technical problems. Scientists know that nuclear and mito- decision, and historical examples—most notably, the Holocaust—
chondrial DNA interact, but these interactions are currently very poorly demonstrate the devastation that results when a small group of individuals
understood. Thus, no one can predict what will happen when an artificial assumes the power to make value judgments based on genetics and race.
combination is created. Moreover, one scientist has compared the proce- And perhaps the most important question of all—and one with
dure to the cellular equivalent of a heart transplant. What if the technique profound implications for society—do scientists ever have the right to
isn’t perfect and maternal mitochondria are accidentally transferred along bioengineer a child?
with the mother’s nucleus? What will happen to the donor ovum’s other
1
organelles? How will the reengineered DNA combination ultimately You can find out more about this condition at: http://ghr.nlm.nih.gov
affect the mother? What if the donor’s mitochondrial DNA passes into /condition/leber-hereditary-optic-neuropathy
codes for this growth factor can be injected alone or within a virus patients report that they have less chest pain and can run longer on
into the heart to stimulate branching of coronary blood vessels. a treadmill.
These additional branches improve coronary circulation, provid- Some of the newest applications of gene therapy are
ing additional oxygen and nutrients to the myocardium. Coronary approaches to correct the errors in transcription and translation
FOCUS on FORENSICS
The Innocence Project
Imagine that you’re a young man who’s been charged with murder. At past criminal convictions in which evidence is highly suspect. As you
your trial, a truck driver who gives “eyewitness” testimony states that remember from Chapter 3, DNA analysis is often a vital tool for crim-
you were the hitchhiker he picked up near the crime scene—but he’s inal identification. However, DNA evidence can also be used to
blind in one eye and admits it was very dark that night. A jailhouse review court findings and potentially overturn a wrongful conviction.
snitch tells the judge that you confessed to the murder—and then, In Dillon’s case, although nearly all of the evidence from his original
rape charges against him are later dropped by the prosecution. A for- murder trial had been lost or destroyed, the blood-stained T-shirt from
mer girlfriend testifies against you—but then recants her testimony the crime was fortunately still available. DNA testing was performed
two weeks later. A scent-dog handler tells the judge and jury that his on the shirt, and the testing showed that the blood belonged to the
dog identified your scent on a bloody T-shirt found near the scene— victim and to another unidentified man. There was no trace of Dillon’s
but the man’s credentials and the dog’s tracking ability are both later DNA on the shirt. With this new evidence, William Dillon was finally
called into question. You maintain that you were five miles away proven innocent, after spending 26 years in prison for a crime that
from the scene at the time the murder occurred, and others confirm someone else committed. He was cleared of all charges by the prose-
your alibi. However, five days later, you’re convicted of first-degree cution, and was freed from prison on December 10, 2008. In June
murder, sentenced to life in prison, and incarcerated. This was the 2011, 30 years after the original murder, cold-case detectives named
nightmarish scenario faced by William Dillon in 1981. four new suspects.
Now fast-forward to 2007: With help from the attorneys of the William Dillon’s case is one of a multitude of decades-old crimi-
Innocence Project, Dillon’s repeated requests for an investigation into nal cases that have been reopened through the work of the Innocence
his conviction were finally granted by a Florida judge. The Innocence Project. To date, the Project’s efforts have exonerated more than 329
Project—an advocacy group composed of attorneys, law students, and individuals using DNA technology, including 18 who had been serv-
volunteers—uses modern DNA testing in its mission of re-examining ing time on death row.
Summary
19.1 Chromosomal Inheritance E. Abnormal combinations of sex individual inherited one domi-
A. Normally, an individual inherits chromosomes include XO nant and one recessive allele
22 pairs of autosomal chromo- (Turner syndrome), XXX (poly-X), and has the dominant pheno-
somes and one pair of sex chro- XXY (Klinefelter syndrome), and type; a homozygous recessive
mosomes. Females are XX and XYY (Jacobs syndrome). individual inherited two
males are XY. 19.2 Genetic Inheritance recessive alleles and has the
B. Amniocentesis and chorionic villi A. Genes control human traits. recessive phenotype. A Pun-
sampling are used to provide Uppercase letters designate nett square can be used to
cell samples for karyotyping fetal dominant alleles; lowercase let- predict the probability of gene
chromosomes. ters designate recessive alleles. inheritance.
C. Nondisjunction during oogenesis B. The genotype represents the C. The inheritance of X-linked
or spermatogenesis explains the genes of an individual, and the alleles differs in males and
inheritance of an abnormal num- phenotype refers to outward females. Males require only one
ber of chromosomes. expression of the gene. A ho- recessive allele to have an
D. The most common autosomal mozygous dominant individual X-linked trait; females require
abnormality is Down syndrome, inherited two dominant alleles two recessive alleles. This
which is due to the inheritance and has the dominant means that males are more likely
of an extra chromosome 21. phenotype; a heterozygous to inherit an X-linked disorder.
Study Questions
1. What is the normal chromosome inher- resulting from inheritance of abnormal 10. Give examples of dominant, recessive,
itance of humans? (p. 446) numbers of sex chromosomes? and X-linked genetic disorders in
2. How is a karyotype prepared? What (p. 449) humans. (p. 453)
are the possible sources for cell 6. Explain autosomal dominant and 11. Describe the function of an allele
samples in an adult? In the fetus? recessive genetic inheritance. using the CF allele as an example.
(pp. 446–447) (pp. 450–451) (pp. 452–453)
3. What is nondisjunction, and when does 7. Explain X-linked allele inheritance in 12. What is gene therapy, and what types
nondisjunction occur during meiosis? humans. (p. 451) of genetic disorders have been treated
(pp. 447–448) 8. Describe how to construct and inter- thus far? (pp. 454, 456–458)
4. What are the characteristics of a person pret a Punnett square. (pp. 451–452) 13. What is a genome? What is genomics,
with Down syndrome? (pp. 448–449) 9. What type of information does a genetic and what might be the benefits of
5. What are the characteristics of the counselor give parents who might pass genomics in the future? (pp. 458–459)
most common human conditions on a genetic disorder? (pp. 452–453)
LearningTerminology
Medical Outcome Questions
Exercise
After studying this chapter, see if you can derive the definitions 1. neogenesis (nēō-jĕn9ĕ-sĭs)
for the medical terms listed at right. Many of the prefixes and 2. regeneration (rē-jĕnĕr-ā9shŭn)
suffixes used to create these terms can be found throughout 3. fetoscope (fē9tō-skōp)
the chapter. For additional help, use McGraw-Hill Connect™ at 4. polydysplasia (pŏlē-dĭs-plā9zē-ŭh)
www.mcgrawhillconnect.com and consult Appendix B. 5. congenital (kŏn-jĕn9ĭ-tăl)
and all of the symptoms of the disease. If untreated, sickle cell anemia is
Chapter 1 often fatal. You can read more about sickle-cell disease in Chapter 11.
Content Check-Up!
1. structural organization; 2. organ systems; 3. organelles; 4. superior; Learning Outcome Questions
5. buccal; 6. horizontal; 7. parietal pleura—b, visceral pericardium—a, vis- 1. atoms; 2. neutrons; 3. ionic, covalent; 4. hydrogen; 5. hydrogen, lower;
ceral peritoneum—c; 8. chest pain, particularly when a person inhales; 6. glucose, energy; 7. glycerol, fatty acid; 8. amino acids, coil, structure or
9. endocrine and nervous; 10. digestive; 11. a; 12. digestive and urinary; configuration; 9. enzymes; 10. DNA, nucleotide.
13. d; 14. b.
Chapter 3
Begin Thinking Clinically
Page 8: Because the child is pointing to the umbilical region, the source of Content Check-Up!
his pain is most likely the small intestine. Two common reasons for intes- 1. a-2, b-3, c-1; 2. Nuclear envelope, Golgi apparatus, lysosomes, vesicles
tinal pain are stretching the small intestine (as when the organ overfills are the components of the endomembrane system. Endoplasmic reticulum
with gas) or irritating the intestinal lining (as in bacterial food poisoning). forms proteins and lipids, the Golgi apparatus forms vesicles, lysosomes
destroy cells or cell parts, and the nuclear membrane contains the nucleus;
Learning Outcome Questions 3. a-2, b-4, c-1, d-3; 4. c; 5. The bacteria were taken into the cell by phago-
1. c; 2. f; 3. g; 4. a; 5. d; 6. c; 7. e; 8. b; 9. a; 10. d; 11. g; 12. f; 13. d; cytosis; 6. a; 7. c; 8. b; 9. d.
14. c; 15. e; 16. a; 17. d; 18. b; 19. g; 20. c; 21. d; 22. e; 23. f; 24. a; 25. b;
26. anatomy; 27. organ; 28. midsagittal or median; 29. homeostasis; Begin Thinking Clinically
30. negative feedback. Page 52: When brain tissue is damaged, fluid escapes into the spaces be-
tween the nerve cells. This swelling can put pressure on the brain (because
Medical Terminology Exercise it’s enclosed by the skull) and cause further brain damage. If a hypertonic
1. above; 2. below; 3. stomach; 4. abdomen; 5. head; 6. thorax; solution flows through the blood vessels supplying the brain, osmosis will
7. sides; 8. eye; 9. back; 10. study; 11. a; 12. a; 13. blood; 14. d; 15. a. cause excess fluid to be returned to the bloodstream.
A-1
A-2 Appendix A
Appendix A A-3
A-4 Appendix A
Appendix A A-5
C–1
Chapter 13 Chapter 17
Opener: © Bruce Grenville Matthews/Photodisc/Getty Images RF; 17.4b:
Opener: ©Photodisc Collection/Getty Images RF; 13.1c_a: © Al Telser/
© Al Telser/McGraw-Hill Education; 17.5(right): © David M. Phillips/Sci-
McGraw-Hill Education; 13.1c_b: © Ed Reschke/Photolibrary/Getty Images;
ence Source; 17.7b: © Anatomical Travelogue/Science Source; 17.10: © Ed
13.1c_c: © Al Telser/McGraw-Hill Education; 13.1c_d: © Ed Reschke; 13.2a:
Reschke/Photolibrary/Getty Images; 17.17a: © Centers for Disease Control
© Ed Reschke/Photolibrary/Getty Images; 13.2b-c: © Ed Reschke; 13.2d-e:
and Prevention; 17.17b: © Biophoto Associates/Science Source; 17.17c:
© Ed Reschke/Photolibrary/Getty Images; 13.4b: Courtesy Dr. Arthur J.
© Melba Photo Agency/Alamy RF; 17Da: © Dave and Les Jacobs/Blend
Olson, The Scripps Research Institute; 13.7d: © Steve Gschmeissner/Science
Images LLC RF; 17Db: © David Raymer/Comet/Corbis; 17E: © Steve Nagy/
Source; 13.9: © JGI/Blend Images LLC RF; 13C: © C. S. Goldsmith and A.
Design Pics RF.
Balish/Centers for Disease Control and Prevention; p. 310: © Jill Braaten/
McGraw-Hill Education.
Chapter 18
Chapter 14 Opener: © Hulton-Deutsch Collection/Historical/Corbis; 18.1: © David M.
Phillips/Science Source; 18.6a: © Lennart Nilsson/Scanpix; 18.8: © James
Opener: © Stockbyte/Getty Images RF; 14.3c: © CNRI/Phototake; 14.4b:
Stevenson/SPL/Science Source; 18.10: © Rune Hellestad/Encyclopedia/
© Ed Reschke; 14.4c: © Nibsc/Getty Images; 14.8: © Burger/Phanie/AGE
Corbis.
Fotostock; 14.12a: © Matt Meadows/Photolibrary/Getty Images; 14.12b:
© Dennis K. Burns, Md Travis G. Brown, Md Walter L. Kemp, Md/McGraw-
Hill Education; 14.12c: © Biophoto Associates/Science Source.
Chapter 19
Opener: © FPG/The Image Bank/Getty Images; 19.1c: © Ermakoff/Sci-
Chapter 15 ence Source; 19.1d-e: © CNRI/Science Source; 19.3: © Jill Cannefax;
19.4a-b: Courtesy of G. H. Valentine, Earl Plunkett; 19A1: © Brand X/
Opener: © Bettmann/Corbis; 15.4b: © Biophoto Associates/Science Source;
SuperStock RF.
15.5c: © Ed Reschke/Photolibrary/Getty Images; 15.7b: © Victor P.
Credits C–2
GI-1 Glossary/Index
Glossary/Index GI-2
GI-3 Glossary/Index
Glossary/Index GI-4
GI-5 Glossary/Index
Glossary/Index GI-6
GI-7 Glossary/Index
Glossary/Index GI-8
GI-9 Glossary/Index
Glossary/Index GI-10
GI-11 Glossary/Index
Glossary/Index GI-12
GI-13 Glossary/Index
Glossary/Index GI-14
GI-15 Glossary/Index
Glossary/Index GI-16
GI-17 Glossary/Index
Glossary/Index GI-18
GI-19 Glossary/Index
Glossary/Index GI-20
GI-21 Glossary/Index
Glossary/Index GI-22
GI-23 Glossary/Index
Glossary/Index GI-24
GI-25 Glossary/Index