Chapter 18
The Cardiovascular System: The Heart
Stroke volume depends to a large extent on the degree to which
venous return stretches cardiac muscle. Approximately 70 ml, it
is the difference between end diastolic volume (EDV) and end
systolic volume (ESV). Anything that influences heart rate or
blood volume influences venous return, hence stroke volume.
Activation of the sympathetic nervous system increases heart rate
and contractility; parasympathetic activation decreases heart rate
but has little effect on contractility. Ordinarily, the heart exhibits
vagal tone.
Chemical regulation of the heart is effected by hormones
(epinephrine and thyroxine) and ions (particularly potassium
and calcium). Ion imbalances severely impair heart activity.
Other factors influencing heart rate are age, sex, exercise, and
body temperature.
Congestive heart failure occurs when the pumping ability of the
heart cannot provide adequate circulation to meet body needs.
Right heart failure leads to systemic edema; leF heart failure
results in pulmonary edema.
Cardiovascular System; Topic: Cardiac Output, pp. 1–11.
Developmental Aspects of the Heart
(pp. 685–687)
Before Birth
(pp. 685–686)
Te heart begins as a simple (mesodermal) tube that is pumping
blood by the fourth week of gestation. Te fetal heart has two
lung bypasses: the foramen ovale and the ductus arteriosus.
Congenital heart defects are the most common of all birth
defects. Te most common of these disorders lead to inadequate
oxygenation of blood or increase the workload of the heart.
Heart Function Throughout Life
(pp. 686–687)
Age-related changes include sclerosis and thickening of the valve
flaps, declines in cardiac reserve, fibrosis of cardiac muscle, and
Risk factors for cardiac disease include dietary factors, excessive
stress, cigarette smoking, and lack of exercise.
trunk. Postganglionic fibers innervate the SA and AV nodes and
the cardiac muscle fibers. Te cardioinhibitory center exerts its
influence via the parasympathetic vagus nerves (X), which project
to the heart wall. Most parasympathetic fibers serve the SA and
AV nodes.
An electrocardiogram (ECG) is a graphic representation
of the cardiac conduction cycle. Te P wave reflects atrial
depolarization. Te QRS complex indicates ventricular
depolarization; the ± wave represents ventricular repolarization.
Cardiovascular System; Topic: Intrinsic Conduction System,
pp. 1–7; Topic: Cardiac Action Potential, pp. 1–10.
Heart Sounds
(pp. 678–679)
Normal heart sounds arise chiefly from turbulent blood flow
during the closing of heart valves. Abnormal heart sounds, called
murmurs, usually reflect valve problems.
Mechanical Events: The Cardiac Cycle
(pp. 679–681)
A cardiac cycle consists of the events occurring during one
heartbeat. During mid-to-late diastole, the ventricles fill and the
atria contract. Ventricular systole consists of the isovolumetric
contraction phase and the ventricular ejection phase. During
early diastole, the ventricles are relaxed and are closed chambers
until the atrial pressure exceeds the ventricular pressure, forcing
the AV valves open. Ten the cycle begins again. At a normal
heart rate of 75 beats/min, a cardiac cycle lasts 0.8 s.
Pressure changes promote blood flow and valve opening and
Cardiovascular System; Topic: Cardiac Cycle, pp. 1–19.
Cardiac Output
(pp. 681–685)
Cardiac output, typically 5 L/min, is the amount of blood
pumped out by each ventricle in 1 minute. Stroke volume is
the amount of blood pumped out by a ventricle with each
contraction. Cardiac output
heart rate
stroke volume.
Multiple Choice/Matching
(Some questions have more than one correct answer. Select the best
answer or answers from the choices given.)
When the semilunar valves are open, which of the following are
2, 3, 5, 6,
1, 2, 3, 7,
1, 3, 5, 6,
2, 4, 5, 7.
____ (1)
coronary arteries fill
____ (2)
AV valves are closed
____ (3)
ventricles are in systole
____ (4)
ventricles are in diastole
____ (5)
blood enters aorta
____ (6)
blood enters pulmonary arteries
____ (7)
atria contract
Te portion of the intrinsic conduction system located in the
superior interventricular septum is the
AV node,
SA node,
AV bundle,
subendocardial conducting network.
An ECG provides information about
cardiac output,
movement of the excitation wave across the heart,
coronary circulation,
valve impairment.
Te sequence of contraction of the heart chambers is
leF chambers followed by right chambers,
both atria
followed by both ventricles,
right atrium, right ventricle, leF
atrium, leF ventricle.
Te fact that the leF ventricular wall is thicker than the right
reveals that it
pumps a greater volume of blood,
blood against greater resistance,
expands the thoracic cage,
pumps blood through a smaller valve.
Te chordae tendineae
close the atrioventricular valves,
prevent the AV valve flaps from everting,
contract the
papillary muscles,
open the semilunar valves.
In the heart, which of the following apply?
Action potentials
are conducted from cell to cell across the myocardium via gap
the SA node sets the pace for the heart as a whole,
spontaneous depolarization of cardiac cells can occur in the
absence of nerve stimulation,
cardiac muscle can continue to
contract for long periods in the absence of oxygen.
all of the
1, 3, 4,
1, 2, 3,
2, 3.
Te activity of the heart depends on intrinsic properties of
cardiac muscle and on neural factors. Tus,
vagus nerve
stimulation of the heart reduces heart rate,
sympathetic nerve
Review Questions
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