Bio2 M2-3
Bio2 M2-3
Bio2 M2-3
skin and its accessory structures, including the hair, melanin… the pigment that gives color to the skin.
nails, sebaceous glands, and sweat glands. The more abundant the melanin… the darker the
skin color. Damage to this layer, such as in severe
SKIN burns, requires skin grafts.
The exterior covering of the body. It weighs
more than 6 pounds in the average adult, and DERMIS
covers more than 3,000 square inches. It is the beneath the epidermis and is composed of
largest organ of the body. It is supplied with blood connective tissue.
vessels and nerves. contains the lymphatics, nerves, nerve endings,
blood vessels, sebaceous and sweat glands,
Functions of SKIN: elastic fibers, and hair follicles.
provides protection. It protects against invasion divided into two layers.
by bacteria and other harmful agents. 1. papillary layer is arranged into microscopic
protects delicate cells beneath the surface from structures that form ridges. These are the
injury. finger- and footprints.
Inhibits excessive loss of water and electrolytes. 2. reticular layer is beneath the papillary
It produces a protective pigmentation to layer; it is white fibrous tissue that supports
protect the body against excessive exposure the blood vessels.
from the sun. connected to underlying tissue by the
helps produce the body’s supply of Vitamin D. subcutaneous tissue.
The skin regulates body temperature. When the subcutaneous tissue or hypodermis is
body is too cold, the skin’s blood vessels composed of adipose and connective tissue. It
constrict. This allows more heat-carrying blood supports, nourishes, insulates, and cushions
to circulate to the muscles and organs. the skin.
When the body is too hot, the blood vessels in
the skin dilate. That brings more blood to the ACCESSORY STRUCTURE
surface for cooling by radiation. At the same HAIR
time, sweat glands secrete more sweat that threadlike structure formed by a group of cells
cools the body when it evaporates. that develop within a hair follicle or socket. Each
The skin provides sensations. It contains hair has a shaft that is visible and a root that is
millions of nerve endings that act as sensory embedded in the follicle.
receptors for pain, heat, cold, and pressure. pilomotor muscle is attached to the side of
When stimulation occurs, nerve impulses are each follicle. It is stimulated by skin irritants,
sent to the cerebral cortex of the brain and the emotional arousal, or cold temperatures, and
brain triggers any necessary response. reacts by contracting. (goose flesh/pimple)
The skin has two layers, the epidermis and the At the base of each hair follicle is a bulb
dermis. enclosing a loop of capillaries. It is called the
hair papilla, and provides nourishment to the
EPIDERMIS hair. It is one of the few living parts of the hair,
4 străta: and is responsible for hair growth.
stratum corneum - the outermost strata of the
epidermis. It is mostly dead cells, filled with a 1. The transparent cuticle covers the hair
protein substance called keratin. It is thicker on the shaft like shingles on a roof, protecting it
soles of the feet than on the eyelids…where there from the elements and chemicals, and
is less pressure. from losing moisture.
stratum lucidum - is a translucent layer lying 2. The cortex provides most of the hair’s
directly beneath the corneum. It may not weight. It contains melanin which
even exist in thinner skin. Cells in this layer are also provides color to the hair, stores oils,
dead or are in the process of dying. provides flexibility and elasticity, and
stratum granulosum - is one or more layers of adds shape to the hair. When the cuticle
cells starting to die and become hard. They are in is damaged and exposes the cortex, hair
the process of keratinization… becoming fibrous looks dull and dry.
protein similar to that in hair and nails. 3. The medulla is a inner hollow core that
stratum germinativum - composed of several runs the length of the shaft
layers of living cells capable of cell division. It is the
SEBACEOUS GLANDS
An oil glands. They have tiny ducts that open
into each hair follicle.
Each sebaceous gland secretes sebum, which
lubricates the hair and skin.
The amount of secretion varies with age,
puberty, and pregnancy.
NAILS
Fingernails and toenails are hard keratin
structures that protect the ends of the fingers
and toes. The nail root, also called the
germinal matrix or nailbed, begins several
millimeters into the finger and extends to the
edge of the white, crescent-shaped lunula.
Growth occurs approximately 1 mm. per week.
The under-surface of the nail plate or body of
the nail has grooves that help anchor it.
The cuticle is also called the
eponychium. It fuses the nail plate and
the skin of the finger together to form a
waterproof barrier.
The hyponychium is under the free
edge of the nail. It also creates a
waterproof barrier, fusing the skin of the
finger to the underside of the nail plate.
A lost finger- or toenail will regenerate.
Ingrown nails are simply those that have
curled down or around and are growing into the
skin. They may become swollen and inflamed. Trim
toenails straight across to avoid this growth pattern.
SUDORIFEROUS GLANDS
sweat glands. About 2 million are distributed
over the surface of the body, more numerous
on the palms of the hands, soles of the feet,
forehead, and axillae or underarms.
Sweat glands produce sweat or perspiration. As
sweat collects on the skin surface, it evaporates
and creates a cooling effect. Sweat also rids the
body of waste through the pores of the skin.
As it accumulates, sweat may become odorous
by the action of bacteria.
The average person loses approximately ½ liter
of fluid through sweating each day.
The Skeletal System The vertebrate skeleton also has cartilage.
Scientists classify skeletons into three categories: Bone tissue replaces cartilage as an
Hydrostatic skeleton is fluid constrained individual develops. In children,
within a layer of flexible tissue. Many bone growth occurs at growth plates
invertebrates have hydrostatic skeletons. made of cartilage.
Exoskeleton protects an animal from the
outside. Animals with exoskeletons must The vertebrate skeleton has several important
periodically molt. functions.
Endoskeleton is an internal support
structure. An endoskeleton grows with the
animal and weighs less than an
exoskeleton, but external soft tissues are
not protected.