Page 28 - Cardiac Nursing

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4 PA R T I / Anatomy and Physiology

Chambers Right Heart
The posterior and septal right atrial walls are smooth, whereas the
The wall thickness of each of the four cardiac chambers reflects
lateral wall and the right atrial appendage (auricle) have parallel
the amount of force generated by that chamber. The two thin-
muscular ridges, termed pectinate muscles. The right auricle ex-
walled atria serve functionally as reservoirs and conduits for blood
tends over the aortic root externally.
that is being funneled into the ventricles; they add a small amount
The inferior wall of the right atrium and part of the superior
of force to the moving blood. The left ventricle, which adds the
wall of the right ventricle are formed by the tricuspid valve (Fig.
greatest amount of energy to the flowing blood, is two to three
1-6). The anterior and inferior walls of the right ventricle are lined
times as thick as the right ventricle. The approximate normal wall
by muscle bundles, the trabeculae carneae, which form a rough-
thicknesses of the chambers are as follows: right atrium, 2 mm;
walled inflow tract for blood. One muscle group, the septomar-
right ventricle, 3 to 5 mm; left atrium, 3 mm; and left ventricle,
ginal trabecula or moderator band, extends from the lower inter-
13 to 15 mm.
ventricular septum to the anterior right ventricular papillary
The interatrial septum between right and left atria extends
muscle.
obliquely forward from right to left. The interatrial septum in-
Another thick muscle bundle, the christa supraventricularis,
cludes the fossa ovalis, a remnant of a fetal structure, the foramen
extends from the septal wall to the anterolateral wall of the right
ovale. The lower portion of the interatrial septum is formed by the
ventricle. The christa supraventricularis helps to divide the right
lower medial right atrial wall on one side and the aortic outflow
ventricle into an inflow and outflow tract. The smooth-walled
tract of the left ventricular wall on the other side. The lower mus-
outflow tract, called the conus arteriosus or infundibulum, extends
cular portion of the interventricular septum extends downward
to the pulmonary artery.
from the upper membranous part of the interventricular septum.
The concave free wall of the right ventricle is attached to the
The clinical significance of these structures has recently received
slightly convex septal wall. The internal right ventricular cavity is
much attention. A pooled analysis of autopsy studies found that
crescent or triangle shaped. The right ventricle also forms a cres-
the prevalence of patent foramen ovale in adults is approximately cent laterally around the left ventricle. Right ventricular contrac-
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26%. This is clinically significant, providing a potential conduit
tion causes the right ventricular free wall to move toward the in-
for a shunt from the right atrium to the left atrium and possibly terventricular septum. This bellows-like action is effective in
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accounting for increased risk of stroke and migraine headache. 6
ejecting large and variable volumes into a low-pressure system
In considering the internal surfaces of the cardiac chambers, it is
(Fig. 1-7).
useful to remember that blood flows more smoothly and with less
Venous blood enters the right atrium from the upper and the
turbulence across walls that are smooth rather than ridged. Blood
lower posterior parts of the atrium through the superior and
pools in appendages or other areas out of the direct blood flow path.

■ Figure 1-6 Schematic diagram of the right interior view of the heart. (From Anatomical Chart Company,
General Anatomy, 2008-05-14 0614, 2008-07-16 2010.)