________________________________________________________________________
Chapter 19
________________________________________________________________________
1. Describe the functions of blood.
A. Blood: is a liquid connective tissue that consists of cells surrounded by a liquid extracellular matrix. The
extracellular matrix is called blood plasma, and it suspends various cells and cell fragments.
B. interstitial fluid: is the fluid that bathes body cells and is constantly renewed by the blood.
C. functions of blood: Blood transports oxygen from the lungs and nutrients from the gastrointestinal tract, which
diffuse from the blood into the interstitial fluid and then into body cells. Carbon dioxide and other wastes move
in the reverse direction, from body cells to interstitial fluid to blood. Blood then transports the wastes to various
organs—the lungs, kidneys, and skin—for elimination from the body. The blood has the following 3 general
functions.
I. Transportation: blood transports oxygen from the lungs to the cells of the body and carbon dioxide
from the body cells to the lungs for exhalation. It carries nutrients from the gastrointestinal tract to
body cells and hormones from endocrine glands to other body cells. Blood also transports heat and
waste products to various organs for elimination from the body.
II. Regulation: Circulating blood helps maintain homeostasis of all body fluids. Blood helps regulate
pH through the use of buffers (chemicals that convert strong acids or bases into weak ones). It also
helps adjust body temperature through the heat-absorbing and coolant properties of the water in
blood plasma and its variable rate of flow through the skin, where excess heat can be lost from the
blood to the environment. In addition, blood osmotic pressure influences the water content of cells,
mainly through interactions of dissolved ions and proteins.
III. Protection: Blood can clot, which protects against its excessive loss from the cardiovascular system
after an injury. In addition, its white blood cells protect against disease by carrying on phagocytosis.
Several types of blood proteins, including antibodies, interferons, and complement, help protect
against disease in a variety of ways.
2. Describe the physical characteristics and principal components of blood.
A. physical characteristics of blood: Blood is denser and more viscous (thicker) than water and feels slightly
sticky. The temperature of blood is 38C (100.4F), about 1C higher than oral or rectal body temperature, and it
has a slightly alkaline pH ranging from 7.35 to 7.45. The color of blood varies with its oxygen content. When
saturated with oxygen, it is bright red. When unsaturated with oxygen, it is dark red. Blood constitutes about
20% of extracellular fluid, amounting to 8% of the total body mass. The blood volume is 5 to 6 liters (1.5 gal) in
an average- sized adult male and 4 to 5 liters (1.2 gal) in an average-sized adult female. The gender difference
in volume is due to differences in body size. Several hormones, regulated by negative feedback, ensure that
blood volume and osmotic pressure remain relatively constant. Especially important are the hormones
aldosterone, antidiuretic hormone, and atrial natriuretic peptide, which regulate how much water is excreted in
the urine
3. List the major components of plasma and explain their importance.
A. components of blood: Whole blood has two components: (1) blood plasma, a watery liquid extracellular matrix
that contains dissolved substances, and (2) formed elements, which are cells and cell fragments. If a sample of
blood is centrifuged (spun) in a small glass tube, the cells (which are more dense) sink to the bottom of the tube
while the plasma (which is less dense) forms a layer on top. Blood is about 45% formed elements and 55%
blood plasma. Normally, more than 99% of the formed elements are cells named for their red color—red blood
cells (RBCs). Pale, colorless white blood cells (WBCs) and platelets occupy less than 1% of the formed
elements.
I. buffy coat: since white blood cells and platelets that occupy less than 1% of blood are less dense
than red blood cells and more dense than blood plasma they create this coating between the red
blood cells and blood plasma in centrifuged blood.
II. Plasma: Blood plasma is about 91.5% water and 8.5% solutes, most of which are proteins.
, a. plasma proteins: proteins that are confined to blood and not found elsewhere in the
body. Most of these proteins are synthesized by hepatocytes (liver cells). Responsible for
colloid osmotic pressure. Major contributors to blood viscosity. Transport hormones
(steroid), fatty acids, and calcium. Help regulate blood pH.
b. Albumins: account for 54% of plasma proteins. It is the smallest and most numerous
plasma protein. It help maintain osmotic pressure, an important factor in the exchange of
fluids across blood capillary walls.
c. Globulins: account for 38% of plasma proteins. They are large proteins (plasma cells
produce immunoglobulins. Immunoglobulins help attack viruses and bacteria. Alpha and
beta globulins transport iron, lipids, and fat-soluble vitamins.
d. Fibrinogen: account for 7% of plasma proteins and are large proteins. Plays essential
role in blood clotting.
e. antibodies or immunoglobulins: Certain blood cells develop into cells that produce
gamma globulins, an important type of globulin. because they are produced during
certain immune responses. Foreign substances (antigens) such as bacteria and viruses
stimulate production of millions of different types of these cells. This type of cell binds
specifically to the antigen that stimulated its production and thus disables the invading
antigen.
III. formed elements: include three principal components: red blood cells, white blood cells, and
platelets
a. red blood cells (RBCs): erythrocytes transport oxygen from the lungs to body cells and
deliver carbon dioxide from body cells to the lungs.
b. white blood cells (WBCs): leukocytes protect the body from invading pathogens and
other foreign substances. There are several types of these cells: neutrophils, basophils,
eosinophils, monocytes, and lymphocytes. Lymphocytes are further subdivided into B
lymphocytes (B cells), T lymphocytes (T cells), and natural killer (NK) cells. Each type
of this cell contributes in its own way to the body’s defense mechanisms.
c. Platelets: the final type of formed element, are fragments of cells that do not have a
nucleus. Among other actions, they release chemicals that promote blood clotting when
blood vessels are damaged. They are the functional equivalent of thrombocytes,
nucleated cells found in lower vertebrates that prevent blood loss by clotting blood.
IV. Hematocrit: is the percentage of total blood volume occupied by red blood cells. A value of 40
indicates that 40% of the volume of blood is composed of RBCs. The normal range of hematocrit for
adult females is 38–46% (average = 42); for adult males, it is 40–54% (average = 47). The hormone
testosterone, present in much higher concentration in males than in females, stimulates synthesis of
erythropoietin (EPO), the hormone that in turn stimulates production of RBCs. Thus, testosterone
contributes to higher values in males. Lower values in women during their reproductive years also
may be due to excessive loss of blood during menstruation. A significant drop in these values
indicates anemia, a lower-than-normal number of RBCs.
V. Polycythemia: the percentage of RBCs is abnormally high, and the hematocrit may be 65% or
higher. This raises the viscosity of blood, which increases the resistance to flow and makes the blood
more difficult for the heart to pump. Increased viscosity also contributes to high blood pressure and
increased risk of stroke. Causes of polycythemia include abnormal increases in RBC production,
tissue hypoxia, dehydration, and blood doping or the use of EPO by athletes.
4. Explain the origin of blood cells.
A. formation of blood cells:
I. hemopoiesis or hematopoiesis: The process by which the elements of blood develop. Before birth,
the elements of blood first occurs in the yolk sac of an embryo and later in the liver, spleen, thymus,
and lymph nodes of a fetus. Red bone marrow becomes the primary site in which elements of blood
develop in the last 3 months before birth, and continues as the source of blood cells after birth and
throughout life.
, II. red bone marrow: is a highly vascularized connective tissue located in the microscopic spaces
between trabeculae of spongy bone tissue. It is present chiefly in bones of the axial skeleton, pectoral
and pelvic girdles, and the proximal epiphyses of the humerus and femur.
III. pluripotent stem cells: is composed of 0.05% to 0.1% of red bone marrow cells. Can be referred to
hemocytoblasts and are derived from mesenchyme (tissue from which almost all connective tissues
develop). These cells have the capacity to develop into many different types of cells. In newborns,
all bone marrow is red and thus active in blood cell production. As an individual ages, the rate of
blood cell formation decreases; red bone marrow in the medullary (marrow) cavity of long bones
becomes inactive and is replaced by yellow bone marrow, which consists largely of fat cells. Under
certain conditions, such as severe bleeding, yellow bone marrow can revert to red bone marrow; this
occurs as blood-forming stem cells from red bone marrow move into yellow bone marrow, which is
then repopulated by these stem cells. In order to form blood cells, these stem cells in red bone
marrow produce two further types of stem cells, which have the capacity to develop into several
types of cells. These stem cells are called myeloid stem cells and lymphoid stem cells. Myeloid stem
cells begin their development in red bone marrow and give rise to red blood cells, platelets,
monocytes, neutrophils, eosinophils, basophils, and mast cells. Lymphoid stem cells, which give rise
to lymphocytes, begin their development in red bone marrow but complete it in lymphatic tissues
Lymphoid stem cells also give rise to natural killer (NK) cells. Although the various stem cells have
distinctive cell identity markers in their plasma membranes, they cannot be distinguished
histologically and resemble lymphocytes.
IV. progenitor cells: a possible derivative from myeloid stem cells. are no longer capable of
reproducing themselves and are committed to giving rise to more specific elements of blood. Some
of these cells are known as colony-forming units (CFUs). Following the CFU designation is an
abbreviation that indicates the mature elements in blood that they will produce: CFU–E ultimately
produces erythrocytes (red blood cells); CFU–Meg produces megakaryocytes, the source of
platelets; and CFU–GM ultimately produces granulocytes (specifically, neutrophils) and monocytes.
Progenitor cells, like stem cells, resemble lymphocytes and cannot be distinguished by their
microscopic appearance alone.
V. precursor cells or blasts: Over several cell divisions they develop into the actual formed elements
of blood. For example, mono- blasts develop into monocytes, eosinophilic myeloblasts develop into
eosinophils, and so on. Precursor cells have recognizable microscopic appearances.
VI. hemopoietic growth factors: regulate the differentiation and proliferation of particular progenitor
cells.
VII. erythropoietin or EPO: Increases the number of red blood cell precursors. Are produced primarily
by cells in the kidneys that lie between the kidney tubules (peritubular interstitial cells). With renal
failure, their release slows and RBC production is inadequate. This leads to a decreased hematocrit,
which leads to a decreased ability to deliver oxygen to body tissues.
VIII. thrombopoietin or TPO: is a hormone produced by the liver that stimulates the formation of
platelets from megakaryocytes. Several different cytokines regulate development of different blood
cell types.
IX. Cytokines: Are small glycoproteins that are typically produced by cells such as red bone marrow
cells, leukocytes, macrophages, fibroblasts, and endothelial cells. They generally act as local
hormones. Also, they stimulate proliferation of progenitor cells in red bone marrow and regulate the
activities of cells involved in nonspecific defenses (such as phagocytes) and immune responses (such
as B cells and T cells).
X. colony stimulating factors (CSFs): an important family of cytokines that stimulate white blood cell
formation.
XI. Interleukins: along with CSFs is another main family of cytokines that stimulate white blood cell
formation.
5. Describe the structure, functions, life cycle and production of red blood cells.
A. red blood cells or erythrocytes:
, I. Hemoglobin: which is a pigment that gives whole blood its red color. A healthy adult male has
about 5.4 million red blood cells per microliter (µL) of blood,* and a healthy adult female has about
4.8 million. (One drop of blood is about 50 µL.) To maintain normal numbers of RBCs, new mature
cells must enter the circulation at the astonishing rate of at least 2 million per second, a pace that
balances the equally high rate of RBC destruction.
II. RBC anatomy: are biconcave discs with a diameter of 7–8 µm. (Recall that 1 µm = 1/25,000 of an
inch or 1/10,000 of a centimeter or 1/1000 of a millimeter.) Mature red blood cells have a simple
structure. Their plasma membrane is both strong and flexible, which allows them to deform without
rupturing as they squeeze through narrow blood capillaries. As you will see later, certain glycolipids
in the plasma membrane of RBCs are antigens that account for the various blood groups such as the
ABO and Rh groups. RBCs lack a nucleus and other organelles and can neither reproduce nor carry
on extensive metabolic activities. The cytosol of RBCs contains hemoglobin molecules; these
important molecules are synthesized before loss of the nucleus during RBC production and
constitute about 33% of the cell’s weigh
III. RBC physiology: Red blood cells are highly specialized for their oxygen transport function.
Because mature RBCs have no nucleus, all of their internal space is available for oxygen transport.
Because RBCs lack mitochondria and generate ATP anaerobically (without oxygen), they do not use
up any of the oxygen they transport. Even the shape of an RBC facilitates its function. A biconcave
disc has a much greater surface area for the diffusion of gas molecules into and out of the RBC than
would, say, a sphere or a cube.
a. Globin: a component that composes hemoglobin. Is made up of four polypeptide chains
(two alpha and two beta chains). CO2 is absorbed by the amino acid part of the
hemoglobin and then releases carbon dioxide as blood flows through the lungs, the
carbon dioxide is released from hemoglobin and then exhaled.
b. Heme: a component that composes hemoglobin. A ringlike non-protein pigment that is
bound to each of the 4 chains. At the center of each heme ring is and iron ion (Fe 2+) that
can combine reversibly with a oxygen molecule. This makes it possible for a hemoglobin
molecule to bind to 4 oxygen molecules. Each oxygen molecule picked up from the
lungs is bound to an iron ion. As blood flows through tissue capillaries, the iron–oxygen
reaction reverses. Hemoglobin releases oxygen, which diffuses first into the interstitial
fluid and then into cells.
c. nitric oxide (NO): Is produced by the endothelial cells that line blood vessels, binds to
hemoglobin. Under some circumstances, hemoglobin releases this molecule. The released
of this molecule causes vasodilation, an increase in blood vessel diameter that occurs
when the smooth muscle in the vessel wall relaxes. Vasodilation improves blood flow and
enhances oxygen delivery to cells near the site of this molecules release.
IV. RBC life cycle: Red blood cells live only about 120 days because of the wear and tear their plasma
membranes undergo as they squeeze through blood capillaries. Without a nucleus and other
organelles, RBCs cannot synthesize new components to replace damaged ones. The plasma
membrane becomes more fragile with age, and the cells are more likely to burst, especially as they
squeeze through narrow channels in the spleen. Ruptured red blood cells are removed from
circulation and destroyed by fixed phagocytic macrophages in the spleen and liver, and the
breakdown products are recycled and used in numerous metabolic processes, including the formation
of new red blood cells. The recycling occurs as follows
1) Macrophages in the spleen, liver, or red bone marrow phagocytize ruptured and worn-
out red blood cells.
2) The globin and heme portions of hemoglobin are split apart.
3) Globin is broken down into amino acids, which can be reused to synthesize other
proteins.
4) Iron is removed from the heme portion in the form of Fe3+, which associates with the
plasma protein transferrin , a transporter for Fe3+ in the bloodstream.
