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
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
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
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
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
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.
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
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, 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
(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.
coronary arteries ﬁll
AV valves are closed
ventricles are in systole
ventricles are in diastole
blood enters aorta
blood enters pulmonary arteries
Te portion of the intrinsic conduction system located in the
superior interventricular septum is the
subendocardial conducting network.
An ECG provides information about
movement of the excitation wave across the heart,
Te sequence of contraction of the heart chambers is
leF chambers followed by right chambers,
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,
open the semilunar valves.
In the heart, which of the following apply?
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,
Te activity of the heart depends on intrinsic properties of
cardiac muscle and on neural factors. Tus,
stimulation of the heart reduces heart rate,