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The Cardiovascular System: Blood
Chapter 13
CHAPTER SUMMARY
This chapter begins with a general introduction to the functions of blood, a description of its physical characteristics, and
an overview of its components. The important characteristics of blood plasma are described. The characteristics of the
formed elements are described in detail and the formation of formed elements is portrayed. Erythrocytes are thoroughly
described with respect to their anatomy, functions, life cycle and numbers, production, and blood group systems.
Leukocytes are also thoroughly described with respect to their anatomy and types, as well as functions. The major
characteristics of platelets are depicted. A glossary of key medical terms associated with blood is provided. This chapter
concludes with a thorough study outline, an excellent self-quiz, critical thinking questions, and answers to questions that
accompany chapter figures.
STUDENT OBJECTIVES
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List and describe the functions of blood.
List the principal physical characteristics of blood.
Describe the principal components of blood.
Explain the origin of blood cells.
Describe the structure, functions, life cycle, and production of red blood cells.
Describe the structure, functions, and production of white blood cells.
Describe the structure, function, and origin of platelets.
LECTURE OUTLINE
A. Introduction (p. 405)
1. The cardiovascular system consists of:
i. blood
ii. heart
iii. blood vessels (arteries, arterioles, capillaries, venules and veins)
2. Blood is a connective tissue composed of a liquid portion called plasma (the matrix) and a cellular portion
consisting of various cells and cell fragments.
3. Interstitial fluid (or tissue fluid) is the fluid that bathes body cells.
4. Blood carries oxygen and nutrients and exchanges these molecules for carbon dioxide and waste molecules
released from body cells into the interstitial fluid.
5. Hematology is the study of blood, blood-forming tissues, and associated disorders.
B. Functions of Blood (p. 406)
1. Blood is a liquid connective tissue that performs three major functions:
i. transportation of oxygen, carbon dioxide, nutrients, heat, wastes, and hormones
ii. regulation of pH, body temperature, and water content of cells
iii. protection against blood loss via clotting, and against foreign microbes and toxins via the action of
phagocytic white blood cells and specialized plasma proteins
C. Physical Characteristics of Blood (p. 406)
1. Blood has the following major characteristics:
i. denser and more viscous than water
ii. temperature of 38 degrees Celsius
iii. pH that normally ranges between 7.35 and 7.45
iv. constitutes about 8% of total body weight
v. average volume of 5 to 6 liters in adult males and 4 to 5 liters in adult females
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D. Components of Blood (p. 406)
1. Blood consists of:
i. blood plasma or plasma, which has the following characteristics (see Table 13.1):
a. straw-colored liquid
b. accounts for about 55% of the volume of blood
c. consists of about 91.5% water and 8.5% solutes
d. the solutes include plasma proteins (e.g., albumins, globulins, and fibrinogen), waste
molecules, nutrient molecules, enzymes, hormones, gases, and electrolytes
ii. formed elements, including the following (see Tables 13.2 and 13.3):
a. erythrocytes or red blood cells (RBCs)
b. leukocytes or white blood cells (WBCs):
- granular leukocytes (granulocytes)
neutrophils
eosinophils
basophils
- agranular leukocytes (agranulocytes)
lymphocytes
T cells
B cells
natural killer cells
monocytes
c. platelets (which are cell fragments)
2. The percentage of total blood volume occupied by RBCs is called the hematocrit.
E. Formation of Blood Cells (p. 409)
1. Blood cells are formed by hemopoiesis or hematopoiesis that occurs (after birth) only in red bone marrow
(myeloid tissue).
2. The formation of all formed elements involves differentiation of cells in the following sequence:
i. pluripotent stem cells differentiate into myeloid stem cells and lymphoid stem cells
ii. myeloid stem cells differentiate into progenitor cells and precursor cells or blasts
iii. progenitor cells, including colony-forming units (CFUs), and precursor cells or blasts ultimately
differentiate into RBCs, platelets, neutrophils and monocytes, as well as eosinophils and basophils
iv. lymphoid stem cells ultimately differentiate into B lymphocytes and T lymphocytes
3. Several hormones called hemopoietic growth factors regulate the differentiation and
proliferation of specific progenitor cells; these include:
i. erythropoeitin or EPO
ii. thrombopoietin or TPO
iii. cytokines including colony-stimulating factors (CSFs) and interleukins
F. Red Blood Cells (Erythrocytes) (p. 411)
1. Greater than 99% of the formed elements in blood are erythrocytes (red blood cells or RBCs).
2. A healthy adult male has about 5.4 million erythrocytes per microliter of blood; a healthy adult female has
about 4.8 million erythrocytes per microliter.
3. Each RBC is a flexible, biconcave disc that lacks a nucleus and other organelles.
4. The cytosol of each RBC contains about 280 million dissolved hemoglobin molecules.
5. Each hemoglobin molecule consists of four globin chains and four heme groups.
6. Hemoglobin can bind reversibly to oxygen (to form oxyhemoglobin); this permits erythrocytes to transport
oxygen from the lungs to other tissues of the body.
7. Hemoglobin can also bind reversibly to carbon dioxide (to form carbaminohemoglobin); this permits
erythrocytes to transport carbon dioxide from the tissues to the lungs to be expelled.
8. Hemoglobin also plays a role in regulation of blood flow and blood pressure.
9. Erythrocytes live only approximately 120 days due to absence of organelles; the latter results in an inability to
replace plasma membrane components that are damaged as RBCs squeeze through narrow capillaries.
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10. Erythropoiesis starts in the red bone marrow and progresses through the following successive stages of
differentiation:
i. proerythroblast
ii. anucleate reticulocyte that enters the bloodstream
iii. erythrocyte
11. Hypoxia stimulates the kidneys to release erythropoietin which in turn stimulates erythropoiesis.
12. There are two major blood group systems; each is based on the presence or absence of genetically determined
cell-surface antigens called isoantigens or agglutinogens:
i. ABO blood grouping system
ii. Rh blood grouping system
G. White Blood Cells (Leukocytes) (p. 413)
1. Anatomy and Types:
i. Leukocytes (white blood cells or WBCs) have a nucleus and do not contain hemoglobin.
ii. Granular leukocytes (granulocytes) have lobed nuclei and are classified according to the types of
granules present in the cytoplasm into:
a. neutrophils
b. eosinophils
c. basophils
iii. Agranular leukocytes (agranulocytes) lack observable granules and are classified into:
a. lymphocytes (including B cells, T cells and natural killer cells)
b. monocytes
- monocytes exit blood vessels and differentiate into macrophages, including fixed
macrophages and wandering macrophages
2. WBC Functions:
i. The life span of the various types of WBCs ranges from several hours to many years; however, most
live for only several days.
ii. The average number of WBCs ranges from 5000 to 10,000 per microliter of blood; therefore the ratio
of RBCs to WBCs is about 700:1
iii. Leukocytosis is an increase in the number of WBCs while leukopenia is an abnormally low level of
WBCs.
iv. The general function of WBCs is to combat microbes and toxins by phagocytosis or immune
responses; this is accomplished as follows:
a. neutrophils and macrophages are active in phagocytosis
b. eosinophils release enzymes that combat histamine in allergic reactions; eosinophils are also
effective against certain parasitic worms
c. basophils (develop into mast cells that) release substances which intensify the inflammatory
reaction
d. B cells destroy bacteria and inactivate their toxins
e. T cells attack viruses, fungi, transplanted cells, cancer cells, and some bacteria; T cells are also
responsible for transfusion reactions, allergies, and rejection of transplanted organs
f. natural killer cells attack a wide variety of infectious microbes and certain spontaneously
arising tumor cells.
H. Platelets (note that these are sometimes called thrombocytes, but the latter is a technically incorrect term in humans
because technically these are not cells) (p. 416)
1. Thrombopoietin stimulates myeloid stem cells to differentiate ultimately into megakaryocytes.
2. Platelets are produced by the shedding of 2000-3000 membrane-enclosed fragments of cytoplasm from each
megakaryocyte.
3. The average number of platelets ranges from 150,000 to 400,000 platelets per microliter of blood.
4. Each platelet is a small disc-shaped structure whose cytoplasm lacks a nucleus.
5. Platelets help repair slightly damaged blood vessels by forming a platelet plug and promoting blood clotting.
6. Platelets have a life span that ranges from 5 to 9 days.
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I. Key Medical Terms Associated with Blood (p. 420)
1. Students should familiarize themselves with the glossary of key medical terms.