pulses because of their smaller size and higher
metabolic rate.- A person in excellent physical condition has a slow
resting pulse because the heart is a more efficient
pump and pumps more blood per beat.
Cardiac Output (see Table 12–2)
- Cardiac output is the amount of blood pumped by
a ventricle in 1 minute. - Stroke volume is the amount of blood pumped by a
ventricle in one beat; average is 60 to 80 mL. - Cardiac output equals stroke volume pulse; aver-
age resting cardiac output is 5 to 6 liters. - Starling’s law of the heart—the more cardiac mus-
cle fibers are stretched, the more forcefully they
contract. - During exercise, stroke volume increases as venous
return increases and stretches the myocardium of
the ventricles (Starling’s law). - During exercise, the increase in stroke volume and
the increase in pulse result in an increase in cardiac
output: two to four times the resting level. - Cardiac reserve is the difference between resting
cardiac output and the maximum cardiac output;
may be 15 liters or more. - The ejection fraction is the percent of its total
blood that a ventricle pumps per beat; average is
60% to 70%.
Regulation of Heart Rate (see Fig. 12–7)- The heart generates its own beat, but the nervous
system brings about changes to adapt to different
situations. - The medulla contains the cardiac centers: the
accelerator center and the inhibitory center. - Sympathetic impulses to the heart increase rate and
force of contraction; parasympathetic impulses
(vagus nerves) to the heart decrease heart rate. - Pressoreceptors in the carotid and aortic sinuses
detect changes in blood pressure. - Chemoreceptors in the carotid and aortic bodies
detect changes in the oxygen content of the blood. - The glossopharyngeal nerves are sensory for the
carotid receptors. The vagus nerves are sensory for
the aortic receptors. - If blood pressure to the brain decreases, presso-
receptors in the carotid sinuses detect this decrease
and send fewer sensory impulses along the glos-
sopharyngeal nerves to the medulla. The accelera-
tor center dominates and sends motor impulses
along sympathetic nerves to increase heart rate and
force of contraction to restore blood pressure to
normal. - A similar reflex is activated by hypoxia.
- Epinephrine from the adrenal medulla increases
heart rate and force of contraction during stressful
situations.
288 The Heart
REVIEW QUESTIONS
- Describe the location of the heart with respect to
the lungs and to the diaphragm. (p. 274) - Name the three pericardial membranes. Where
is serous fluid found and what is its function?
(p. 274) - Describe the location and explain the function of
endocardium. (p. 274) - Name the veins that enter the right atrium; name
those that enter the left atrium. For each, where
does the blood come from? (p. 275) - Name the artery that leaves the right ventricle;
name the artery that leaves the left ventricle. For
each, where is the blood going? (p. 275) - Explain the purpose of the right and left AV valves
and the purpose of the aortic and pulmonary semi-
lunar valves. (p. 275)
7. Describe the coronary system of vessels and
explain the purpose of coronary circulation. (p.
278)
8. Define systole, diastole, and cardiac cycle.
(p. 278)
9. Explain how movement of blood from atria to
ventricles differs from movement of blood from
ventricles to arteries. (p. 279) - Explain why the heart is considered a double
pump. Trace the path of blood from the right
atrium back to the right atrium, naming the
chambers of the heart and their vessels through
which the blood passes. (pp. 275, 277) - Name the parts, in order, of the cardiac conduc-
tion pathway. Explain why it is the SA node that
generates each heartbeat. State a normal range of
heart rate for a healthy adult. (pp. 279–283)