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Chapter 18
I.
The Heart
Location and Orientation Within the Thorax (p. 500, Figs. 18.1–18.2).
A. The heart is a double pump; the right side pumps blood to the lungs for oxygenation, i.e., the
pulmonary circuit; the left side pumps blood throughout the body to nourish tissues, i.e., the systemic
circuit (p. 500, Fig. 18.1).
B. The four chambers are the right and left atria (receiving chambers) and the right and left ventricles
(pumping chambers) (p. 500, Fig. 18.1).
C. The cone-shaped heart lies obliquely in the mediastinum; the size of a fist, approximately 250–300
grams, its apex points toward the left hip and the broad posterior base is directed toward the left
shoulder (p. 500, Fig. 18.2).
II.
Structure of the Heart (pp. 500–503, Figs. 18.3–18.5).
A. The heart is enclosed by the pericardium; pericardium consists of a superficial layer (the fibrous
pericardium and parietal layer of serous pericardium), and a deeper visceral layer of the serous
pericardium that covers the heart surface (p. 502, Fig. 18.3).
B. The wall of the heart has three layers: a superficial epicardium (same as the visceral layer of serous
pericardium), a middle myocardium (the cardiac muscle), and a deep endocardium (heart lining) (p.
502, Fig. 18.3–18.4).
C. The heart has four chambers (pp. 502–503, Fig. 18.5).
1. Right and left atria are located superiorly and separated by an interatrial septum.
2. Right and left ventricles are located inferiorly and separated by an interventricular septum.
III.
Pathway of Blood Through the Heart (pp. 503–508, Figs. 18.6–18.7).
A. The pathway of blood through the heart begins with a drop of oxygen-poor systemic blood arriving at
the right atrium and terminates with an oxygen-rich drop of blood leaving the left ventricle (p. 503 and
507–508, Fig. 18.6).
B. A sequence of atrial contractions and ventricular contractions (called a heartbeat) propels blood
through the heart (p. 507).
C. The muscular walls of the right and left ventricles reflect differential pressures in the pulmonary and
systemic circuits (pp. 507–508, Fig. 18.7).
IV.
Heart Valves (pp. 508–511, Figs. 18.8–18.11).
A. The four heart valves are the two atrioventricular valves and the two semilunar valves (p. 508, Fig.
18.8).
1. The right AV valve is the tricuspid and the left AV valve is called the bicuspid or mitral.
2. The two semilunar valves are the pulmonary semilunar valve and the aortic semilunar valve.
B. A valve consists of two or three flaps of endocardium called cusps; the AV valves lie at the junctions
between the atria and ventricles; the semilunar valves lie at the junctions between the ventricles and
great arteries (p. 508, Fig. 18.8).
C. Heart valves open to allow blood to flow and close to prevent backflow in response to differences in
blood pressure on each side of the valves (p. 508, Fig. 18.9–18.10).
D. Heart sounds (the familiar “lub-dup”) are produced by the closing of the valves (pp. 509–511, Fig.
18.11).
V.
Fibrous Skeleton (p. 511, Fig. 18.8a).
A. The fibrous skeleton of the heart surrounds the heart valves and functions in several ways, one of which
is to anchor the valve cusps (p. 511, Fig. 18.8a).
VI.
Conducting System and Innervation (pp. 511–512, Figs. 18.12–18.13).
A. Heart muscle generates and conducts electrical impulses; the intrinsic production of impulses can be
altered by extrinsic neural controls (p. 511).
B. The conducting system of the heart is a series of specialized cardiac muscle cells that carries impulses
throughout the heart; among the several components are the SA node and AV node (pp. 511–512, Fig.
18.12).
C. Innervation to the heart is served by visceral sensory fibers, parasympathetic fibers, and sympathetic
fibers; parasympathetic fibers slow the heart rate and sympathetic fibers increase the heart rate (p. 512,
Fig. 18.13).
VII.
Blood Supply to the Heart (pp. 512–514, Fig. 18.14).
A. Coronary arteries supply oxygenated blood to the heart muscle; cardiac veins drain the deoxygenated
blood from the heart (pp. 512–514, Fig. 18.14).
VIII.
Disorders of the Heart (pp. 514–516).
A. Coronary artery disease is caused by atherosclerotic blockage of the coronary arteries (p. 514).
B. Heart failure is a progressive weakening of the heart as it fails to keep pace with the demands of
pumping blood and thus cannot meet the body’s need for oxygenated blood (p. 516).
C. Disorders of the conduction system include atrial and ventricular fibrillation (p. 516).
IX.
The Heart Throughout Life (pp. 516–519, Fig. 18.15–18.17).
A. The embryonic heart starts pumping around day 22 and four chambers are apparent; four final
chambers are defined during month two (pp. 516–517, Figs. 18.15–18.16).
B. Congenital heart defects mostly are traced to month two of development
(p. 518, Fig. 18.17).
C. Age-related changes that affect the heart are hardening and thickening of the cusps of the heart valves
and fibrosis of cardiac muscle (p. 519).