17
Blood
Overview: Blood Composition
and Functions
(pp. 632–633)
Components (p. 632)
Physical Characteristics and Volume (p. 632)
Functions (pp. 632–633)
Blood Plasma
(p. 633)
Formed Elements
(pp. 634–646)
Erythrocytes (Red Blood Cells) (pp. 634–640)
Leukocytes (White Blood Cells)
(pp. 640–645)
Platelets (pp. 645–646)
Hemostasis
(pp. 646–651)
Step 1: Vascular Spasm (p. 646)
Step 2: Platelet Plug Formation
(pp. 646–647)
Step 3: Coagulation (pp. 647–649)
Clot Retraction and Fibrinolysis (p. 649)
Factors Limiting Clot Growth or
Formation (p. 649)
Disorders of Hemostasis (pp. 650–651)
Transfusion and Blood Replacement
(pp. 651–653)
Transfusing Red Blood Cells (pp. 651–653)
Restoring Blood Volume (p. 653)
Diagnostic Blood Tests
(pp. 653–654)
Developmental Aspects of Blood
(p. 654)
B
lood is the river of life that surges within us,
transporting nearly
everything that must be carried from one place to another. Long before modern
medicine, blood was viewed as magical—an elixir that held the mystical force of
life—because when it drained from the body, life departed as well. Today, blood still has
enormous importance in the practice of medicine. Clinicians examine it more oFen than
any other tissue when trying to determine the cause of disease in their patients.
In this chapter, we describe the composition and functions of this life-sustaining fluid
that serves as a transport “vehicle” for the organs of the cardiovascular system (
cardio
5
heart,
vasc
5
blood vessels). To get started, we need a brief overview of blood circulation,
which is initiated by the pumping action of the heart. Blood exits the
heart
via
arteries
,
which branch repeatedly until they become tiny
capillaries
. By diffusing across the capil-
lary walls, oxygen and nutrients leave the blood and enter the body tissues, and carbon
dioxide and wastes move from the tissues to the bloodstream. As oxygen-deficient blood
leaves the capillary beds, it flows into
veins
, which return it to the heart. ±e returning
631
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