556
UNIT FOUR
Auricle of right atrium
Right ventricle
Pericardial cavity
Left ventricle
Heart (covered by
visceral pericardium)
Pulmonary trunk
Auricle of left atrium
Cut edge of
parietal pericardium
Fibrous pericardium
Anterior interventricular
sulcus
Aorta
Right lung
Left lung
Diaphragm
Superior
vena cava
FIGURE 15.4
The heart is within the mediastinum
and is enclosed by a layered pericardium.
Endocardium
Myocardium
Epicardium
(visceral pericardium)
Coronary
blood vessel
Pericardial
cavity
Parietal
pericardium
Fibrous
pericardium
FIGURE 15.5
The heart wall has three layers: an endocardium, a
myocardium, and an epicardium.
these grooves is the
atrioventricular
(coronary)
sulcus
(a
tre-o-ven-trik
u-lar sul
kus), which encircles the heart
between the atria and ventricles. Two
interventricular
(anterior and posterior)
sulci
mark the septum that separates
the right and left ventricles (see F
g. 15.4).
When increasing blood volume stretches muscle cells associated with
the atria, the cells secrete a peptide hormone called
atrial natriuretic
peptide
(ANP). ANP inhibits release of renin from the kidneys and of
aldosterone from the adrenal cortex. The result is increased excretion
of sodium ions and water from the kidneys and lowered blood volume
and blood pressure. Researchers are investigating use of ANP to treat
high blood pressure.
PRACTICE
5
Describe the layers of the heart wall.
6
Name and locate the four chambers of the heart.
7
Name the oriF
ces between the upper and the lower chambers of
the heart.
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