Chapter 20 - The Cardiovascular System - Blood Functions of Blood

Blood
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Chapter 20 - The Cardiovascular System - Blood

Functions of Blood
1. Transportation of dissolved gases
2. Distribution of nutrients
3. Transportation of metabolic wastes
4. Delivery of enzymes and hormones
5. Stabilization of pH and electrolytes
6. Prevention of fluid losses (clotting reaction)
7. Defense against toxins and pathogens
8. Stabilization of body temperature
Composition of Blood
Blood has two components:
1. Plasma
The liquid matrix of blood.
Plasma contains dissolved proteins and numerous dissolved solutes.
2. Formed Elements
a. Red blood cells (rbc's)
b. White blood cells (immune system)
c. Platelets (clotting mechanism)
http://droualb.faculty.mjc.edu/Lecture%20Notes/Unit%204/cardiovascular-blood%20with%20figures.htm
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Characteristics of whole blood:

Blood is more viscous than water. Plasma is 1.5 times, and whole blood is 5.0 times, the viscosity of
water.
Blood has an alkaline pH being in the range of 7.35 to 7.45.
Blood has a temperature slightly higher than core body temperature (38o C vs. 37oC).
Plasma
The components of plasma include:
1. Water is the major component (about 92%) and is the solvent for organic and inorganic molecules.
2. Electrolytes include sodium, potassium, chloride, calcium, magnesium, bicarbonate, phosphate and
sulfate.
3. Nutrients such as glucose, lipids and amino acids.
4. Blood gases include oxygen, carbon dioxide and nitrogen.
5. Regulatory substances include hormones and enzymes.
6. Plasma proteins.
Make up about 7% of plasma and fall into three major classes:
a. Albumins
Albumins make up roughly 60% of all plasma proteins and are a major contributor to osmotic
pressure.
Albumins are the smallest of the three and serve as carriers for hormones, metabolites and drugs.
b. Globulins
These proteins make up about 35%. Immunoglobulins are produced by lymphocytes and other
globulins are produced by the liver.
The nonimmune globulins serve as transport globulins for ions, hormones and other compounds.
c. Fibrinogen
This is the largest protein but only comprises about 4% of plasma proteins. It participates in the
clot formation when it is transformed into fibrin.
Blood plasma minus the fibrinogen and other clotting proteins is called serum.
Albumin and globulin form complexes with lipids that are called lipoproteins that enable insoluble
lipids to be transported throughout the body.
Formed Elements
Red Blood Cells (RBCs) a.k.a. erythrocytes
Rbc's constitute the largest component of the formed elements (99.9%).
The hematocrit is the percentage volume of blood contributed by the formed elements. It is also
called volume of packed red cells (VPRC) and packed cell volume (PCV).
The normal hematocrit is about 46 (40 to 54) in men, and 42 (37 to 47) in women.
Structure of RBCs
Rbc's are highly specialized cells that lack a nucleus, mitochondria or ribosomes. Their ability to
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transport O2 and CO2 is due to the presence of hemoglobin and other protein within the cell.
The biconcave shape of the rbc's increases the surface area for exchange and enhances the strength
and flexibility of the cells.
The biconcave shape enables rbc's to move more quickly through capillaries by forming stacks called
rouleaux and the ability of the cell to bend upon itself enables the cells to squeeze through smaller
capillaries.
RBC life span
The loss of protein making organelles (nucleus, ribosomes) and other organelles (mitochondria)
decrease the ability of rbc's to produce structural proteins and enzymes. This combined with the wear
and tear that rbc's experience cause these cells to have a short life span.
The typical rbc's live about 120 days before bursting or being phagocytized.
RBCs and Hemoglobin
Hemoglobin (Hb) makes up 95% of the protein within the rbc's. Hemoglobin is a red pigment that is
bright red (arterial blood) when combined with oxygen but becomes a deep red color (venous blood)
when deoxygenated.
On a molecular level, hemoglobin consists of four protein subunits, two alpha hemoglobin units and
two beta hemoglobin units. Each hemoglobin subunit holds a molecule called heme that has an iron ion
that can reversibly bind with oxygen. The hemoglobin molecule can also reversibly bind with CO2 and
about 23% of CO2 is carried in this way.
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Hemoglobin enables rbc's to pick up O2 and give up CO2 in the lungs and release O2 and pick up CO2
in the peripheral tissues.
White Blood Cells (WBCs) a.k.a. leukocytes
Leukocytes perform their primary functions in the peripheral tissues where they are present in large
numbers. The cardiovascular system is primarily a means to travel to the peripheral tissues.
Wbc's leave the circulation by the process of diapedesis that enables them to squeeze between
endothelial cells. They are attracted to specific locations by chemotaxis by which cells use chemical
gradients to guide their movements.
Leukocytes defend against invasion by pathogens and help the body remove toxins, wastes and
damaged cells.
When there are inadequate numbers of wbc's this condition is called leukopenia; when there is an
excessive number of wbc's this condition is called leukocytosis.
There are two major classes of white blood cells:
1. Granular Leukocytes which have specific granules in their cytoplasm.
2. Agranular Leukocytes which lack specific granules in their cytoplasm.
Granular Leukocytes
Neutrophils
Neutrophils are the most numerous wbc constituting about 70% of circulating wbc's in a normal
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individual.
The specific granules of neutrophils contain lysozyme and other bacteriostatic and bacteriocidal
agents.
The nucleus is dense and contorted with expanded regions connected by slender threads so that the
nucleus may appear as beads on a string. Because of this appearance these cells have be called
polymorphonuclear cells or PMN's.
Neutrophils are highly mobile and are the first to arrive at an injury site. They actively phagocytize
bacteria and cellular debris. They die quickly but release chemicals recruit other leukocytes to the
troubled site.
Eosinophils
Eosinophils have specific granules that stain with eosin an acidic red dye and the nucleus is
bilobed.
These cells are 2 to 4% of the circulating white blood cells in a normal individual.
Eosinophils phagocytize antigen-antibody complexes and releases chemicals that moderates the
deleterious effects of inflammatory reactions.
The specific granules also have chemicals that are effective against parasites, particularly
helminthic parasites.
Eosinophil counts increase during allergic reactions and parasitic infections.
Basophils
Basophils are the rarest of the wbc's (less than 1%) and have specific granules that stain with basic
dyes.
The specific granules of basophils contain vasoactive chemicals similar to those of mast cells
(histamine and heparin).
When released, the chemicals of the specific granules exaggerate the inflammatory response by
increasing vascular permeability.
Basophils are involved with hypersensitivity reactions and anaphylaxis.
Agranular Leukocytes
Monocytes
Monocytes constitute about 2 to 8% of wbc's and are the largest wbc (2-3 times the rbc). They
have an indented nucleus and lack specific granules.
Monocytes remain in the blood for about 3 days and enter the tissues to become the macrophages
that are found in various tissues including histiocytes in connective tissues, osteoclasts in bone,
Kupffer cell in liver and macrophages in various other tissues. Hence, they form a part of the
monocytes-macrophage system.
Macrophages arrive at a site of injury or invasion after neutrophils and phagocytizes bacteria, other
cells and tissue debris. They also release chemotaxic chemicals that attract other cells of the immune
system to the site.
Active macrophages also attract fibroblasts to the site to begin repair and the construction of new
tissue.
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Lymphocytes
Lymphocytes form about 20 to 30% of wbc in the normal individual and most have a large, purplestaining nucleus surrounded by a thin halo of cytoplasm.
Lymphocytes are responsible for specific immunity or the ability to attack pathogens or foreign
proteins on an individual basis.
Three types of lymphocytes are recognized:
T cells
T lymphocytes are responsible for cell-mediated immunity. They attack foreign cell directly.
A subclass of these cells is attacked by the HIV virus.
B cells
B lymphocytes are responsible for humoral immunity. When activated, B cells transform into
plasma cells that produce antibody, also called immunoglobulins.
NK cells (natural killer cell)
These cells constitute about 5 - 10% of lymphocytes and are named for their ability to kill
certain types of transformed cells. These cells include cells infected with a virus and cancer cells.
Platelets a.k.a. Thrombocytes
Platelets represent small, discoid-shaped fragments of cytoplasm that are involved in the
surveillance of blood vessels, blood clot formation and tissue repair.
Platelets are continually produced in bone marrow by large cells called megakaryoctyes. Platelets
are produced as the cytoplasm of megakaryoctes becomes fragmented and breaks off as individual
platelets.
An abnormal platelet count is called thrombocytopenia and an excessive number of platelets is
called thrombocytosis.
Platelets participate in the clotting system which is an important aspect of hemostasis
Platelets function as part of the clotting mechanism by:
1. Transporting chemicals involved in the initiation and control of the clotting process.
2. Formation of a temporary patch in the wall of damaged blood vessels.
3. Contraction of the clot after it has formed.
Hemopoiesis
Hemopoiesis is the process of blood cell formation from stem cells.
Erythropoiesis
Erythropoiesis refers specifically to the formation of erythrocytes or rbc's. Red bone marrow is the
primary site of erythropoiesis in the adult.
Erythropoiesis requires adequate supplies of amino acids, iron and vitamin B12. (Lack of vitamin
B12 causes pernicious anemia.)
Erythropoietin (EPO) is a hormone primarily released by the kidneys that stimulates
erythropoiesis. (This hormone is sometimes involved in athletic doping scandals.)
Leukopoiesis
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Leukopoiesis refers to the production of white blood cells from stem cells.
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