LEARNING OBJECTIVES
INTRODUCTION TO
THE CARDIOVASCULAR
T
SYSTEM
I
Understanding the concepts presented in this chapter will enable the student to:
Explain why large organisms require a circulatory system, while single-cell and
small multicellular organisms do not.
Explain the significance of the series and parallel arrangement of the
cardiac chambers, pulmonary circulation, and major organs of the systemic
circulation.
Describe the pathways for the flow of blood through the heart chambers and
large vessels associated with the heart.
Explain the importance of negative feedback systems for the control of arterial
blood pressure.
THE NEED FOR A CIRCULATORY
SYSTEM
All living cells require metabolic substrates
(e.g., oxygen, amino acids, glucose) and a
mechanism by which they can remove by-
products of metabolism (e.g., carbon dioxide,
lactic acid). Single-cell organisms exchange
these substances directly with their environ-
ment through diffusion and cellular transport
systems. In contrast, most cells of large organ-
isms have limited or no exchange capacity
with their environment because their cells are
not in contact with the outside environment.
Nevertheless,
exchange
with
the
outside
environment must occur for the cells to func-
tion. To accomplish this necessary exchange,
large organisms have a sophisticated system
of blood vessels that facilitates the exchange
of substances between cells and blood and
between blood and environment. The small-
est of these blood vessels, capillaries, are in
close proximity to all cells in the body, thereby
permitting exchange to occur. For example,
each cell in skeletal muscle is surrounded by
two or more capillaries. This arrangement of
capillaries around cells ensures that exchange
can occur between blood and surrounding
cells.
Exchange between blood and the outside
environment occurs in several different organs:
lungs, gastrointestinal tract, kidneys, and skin.
As blood passes through the lungs, oxygen
and carbon dioxide are exchanged between
the blood in the pulmonary capillaries and the
gases found within the lung alveoli. Oxygen-
enriched blood is then transported to the organs
where the oxygen diffuses from the blood into
the surrounding cells. At the same time, carbon
dioxide, a metabolic waste product, diffuses
from the tissue cells into the blood and is trans-
ported to the lungs, where exchange occurs
between blood and alveolar gases.
Blood passing through the intestine picks
up glucose, amino acids, fatty acids, and
other ingested substances that have been
transported from the intestinal lumen into
the blood in the intestinal wall by the cells
lining the intestine. The blood then delivers
these substances to organs such as the liver
for additional metabolic processing and to
cells throughout the body as an energy source.
1
CHAPTER
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