CHAPTER 4 • CARDIAC FUNCTION
61
Aorta
SVC
Pulmonic
Valve
Tricuspid
Valve
Pulmonary Artery
Pulmonary
Veins
Mitral Valve
Aortic Valve
Chordae
Tendineae
Papillary
Muscle
Septum
■ FIGURE 4.1 Anatom y of the heart. SVC, superior vena cava;
IVC,
inferior vena cava;
RA,
right atrium;
RV,
right ventricle;
LA,
left atrium;
LV,
left ventricle.
from the superior and inferior vena cavae,
which carry blood returning from the systemic
circulation. The right atrium is a highly disten-
sible chamber that can easily expand to accom-
modate the venous return at a low pressure (0
to 4 mm Hg). Blood flows from the right atrium,
across the tricuspid valve (right atrioventricu-
lar [AV] valve), and into the right ventricle. The
free wall of the right ventricle wraps around
part of the larger and thicker left ventricle. The
outflow tract of the right ventricle is the pulmo-
nary artery, which is separated from the ven-
tricle by the semilunar pulmonic valve. Blood
returns to the heart from the lungs via four pul-
monary veins that enter the left atrium. Blood
flows from the left atrium, across the mitral
valve (left AV valve), and into the left ventricle.
The left ventricle has a thick muscular wall that
allows it to generate high pressures during con-
traction. The left ventricle ejects blood across
the aortic valve and into the aorta.
The tricuspid and mitral valves have fibrous
strands (chordae tendineae) on their leaflets
that attach to papillary muscles located on
the respective ventricular walls. The papillary
muscles contract when the ventricles con-
tract. This generates tension on the valve leaf-
lets via the chordae tendineae, preventing the
valves from bulging back and leaking blood
into the atria (i.e., preventing regurgitation)
as the ventricles develop pressure. The semi-
lunar valves (pulmonic and aortic) do not
have analogous attachments.
Autonomic Innervation
Autonomic innervation of the heart plays an
important role in regulating cardiac function.
The heart is innervated by parasympathetic
(vagal) and sympathetic efferent fibers (see
Chapter 6 for details on the origin of these
autonomic nerves). The right vagus nerve
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