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P A R T 8
Drugs acting on the cardiovascular system
CHAPTER SUMMARY
■■
The heart is a hollow muscle that is divided into a
right and a left side by a thick septum and into four
chambers—the two upper atria and the two lower
ventricles. The right side of the heart receives all of
the deoxygenated blood from the body through the
veins and directs it into the lungs. The left side of
the heart receives oxygenated blood from the lungs
and pumps it out to every cell in the body through
the arteries.
■■
The heart is responsible for pumping oxygenated
blood to every cell in the body and for picking up
waste products from the tissues.
■■
The cardiac cycle consists of a period of rest, or
diastole, when blood is returned to the heart by veins,
and a period of contraction, or systole, when the
blood is pumped out of the heart.
■■
The heart muscle possesses the properties of
automaticity (the ability to generate an action
potential in the absence of stimulation) and
conductivity (the ability to rapidly transmit an action
potential).
■■
The heart muscle is stimulated to contract by
impulses generated in the heart, not by stimuli
from the brain. The autonomic nervous system can
affect the heart to increase (sympathetic) or decrease
(parasympathetic) activity.
■■
In normal sinus rhythm, cells in the SA node generate
an impulse that is transmitted through the atrial
bundles and delayed slightly at the AV node before
being sent down the bundle of His into the ventricles.
When cardiac muscle cells are stimulated, they
contract.
■■
Alterations in the generation of conduction
of impulses in the heart cause arrhythmias
(dysrhythmias), which can upset the normal balance
in the cardiovascular system and lead to a decrease in
cardiac output, affecting all of the cells of the body.
■■
Heart muscle contracts by the sliding of actin and
myosin filaments in a functioning unit called a
sarcomere. Contraction requires energy and calcium
to allow the filaments to react with each other and
slide together.
■■
The heart muscle needs a constant supply of blood,
which is furnished by the coronary arteries. Increase
in demand for oxygen can occur with changes in
heart rate, preload, afterload or stretch on the muscle.
■■
The cardiovascular system is a closed pressure system
that uses arteries (muscular, pressure or resistance
vessels) to carry blood from the heart, veins (flexible,
distensible capacitance vessels) to return blood to the
heart and capillaries (which connect arteries to veins)
to keep blood flowing from areas of high pressure to
areas of low pressure.
■■
Blood pressure is maintained by stimulus from the
sympathetic system and reflex control of blood
volume and pressure by the renin–angiotensin system
and the aldosterone–ADH system. Alterations in
blood pressure (hypotension or hypertension) can
upset the balance of the cardiovascular system and
lead to problems in blood delivery.
■■
Fluid shifts out of the blood at the arterial ends
of capillaries to deliver oxygen and nutrients to
the tissues. It moves out due to the hydrostatic or
fluid pressure of the arterial side of the system.
Fluid returns to the system at the venous end of the
capillaries because of the oncotic pull of proteins in
the vessels. Disruptions in these pressures can lead to
oedema or loss of fluid in the tissues.
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ONLINE RESOURCES
An extensive range of additional resources to enhance teaching
and learning and to facilitate understanding of this chapter may
be found online at the text’s accompanying website, located on
thePoint at
These include Watch and
Learn videos, Concepts in Action animations, journal articles,
review questions, case studies, discussion topics and quizzes.
WEB LINK
To explore the virtual cardiovascular system, consult
the following Internet source:
BIBLIOGRAPHY
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Libby, P. (2012).
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Goodman, L. S., Brunton, L. L., Chabner, B. & Knollmann, B. C.
(2011).
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Essentials of Pathophysiology: Concepts
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Pathophysiology: Concepts of Altered Health
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