Some of the waste products of these cells are
taken up by the blood and transported to
other organs for metabolic processing and
final elimination into the outside environ-
ment through either the gastrointestinal tract
or the kidneys.
Cells require a proper balance of water and
(e.g., sodium, potassium,
calcium) to function. The circulation trans-
ports ingested water and electrolytes from
the intestine to cells throughout the body,
including those of the kidneys, where exces-
sive amounts of water and electrolytes can be
eliminated in the urine.
The skin also serves as a site for exchange
of water and electrolytes (through sweating),
and for exchange of heat, which is a major by-
product of cellular metabolism that must be
removed from the body. Blood flow through
the skin regulates heat loss from the body.
In summary, the ultimate purpose of the
cardiovascular system is to facilitate exchange
of gases, fluid, electrolytes, large molecules,
and heat between cells and the outside envi-
ronment. The heart and vasculature ensure
that adequate blood flow is delivered to organs
so that this exchange can take place.
The cardiovascular system has two primary
components: the heart and blood vessels. A
third component, the lymphatic system, does
not contain blood, but nonetheless serves an
important exchange function in conjunction
with blood vessels.
The heart can be viewed functionally as
two pumps with the pulmonary and systemic
circulations situated between the two pumps
(Fig. 1.1). The pulmonary circulation is the
blood flow within the lungs that is involved
in the exchange of gases between the blood
and alveoli. The systemic circulation is com-
prised of all the blood vessels within and out-
side of organs excluding the lungs. The right
side of the heart comprises the right atrium
and the right ventricle. The right atrium
receives venous blood from the systemic cir-
culation, and the right ventricle pumps it into
the pulmonary circulation where oxygen and
carbon dioxide are exchanged between the
blood and alveolar gases. The left side of the
heart comprises the left atrium and the left
ventricle. The blood leaving the lungs enters
Systemic Circulation
■ FIGURE 1.1 Overview of the cardiovascular system. The right side of the heart, pulmonary circulation,
left side of the heart, and systemic circulation are arranged in series. RA, right atrium;
right ventricle;
pulmonary artery; Ao, aorta;
left atrium;
left ventricle.
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