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The heart chambers
The right atrium (Fig. 7.3)
ventricle.
• The pulmonary valve (see below) is situated at the top of the
• Receives deoxygenated blood from the inferior vena cava below and
infundibulum. It is composed of three semilunar cusps. Blood flows
from the superior vena cava above. • The infundibulum is the smooth walled outflow tract of the right
• Receives the coronary sinus in its lower part (p. 23). through the valve and into the pulmonary arteries via the pulmonary
• The upper end of the atrium projects to the left of the superior vena trunk to be oxygenated in the lungs.
cava as the right auricle.
• The sulcus terminalis is a vertical groove on the outer surface of the The left atrium
atrium. This groove corresponds internally to the crista terminalisaa • Receives oxygenated blood from four pulmonary veins which drain
muscular ridge which separates the smooth walled atrium (derived posteriorly.
from the sinus venosus) from the rest of the atrium (derived from the • The cavity is smooth walled except for the atrial appendage.
true fetal atrium). The latter contains horizontal ridges of musclea • On the septal surface a depression marks the fossa ovalis.
musculi pectinati. • The mitral (bicuspid) valve guards the passage of blood from the left
• Above the coronary sinus the interatrial septum forms the posterior atrium to the left ventricle.
wall. The depression in the septumathe fossa ovalisarepresents the
site of the foramen ovale. Its floor is the fetal septum primum. The The left ventricle (Fig. 7.4)
upper ridge of the fossa ovalis is termed the limbus, which represents • The wall of the left ventricle is considerably thicker than that of the
the septum secundum. Failure of fusion of the septum primum with the right ventricle but the structure is similar. The thick wall is necessary to
septum secundum gives rise to a patent foramen ovale (atrial septal pump oxygenated blood at high pressure through the systemic circula-
defect) but as long as the two septa still overlap, there will be no func- tion. Trabeculae carneae project from the wall with papillary muscles
tional disability. A patent foramen gives rise to a left–right shunt. attached to the mitral valve cusp edges by way of chordae tendineae.
• The vestibule is a smooth walled part of the left ventricle which is
The right ventricle located below the aortic valve and constitutes the outflow tract.
• Receives blood from the right atrium through the tricuspid valve (see
below). The edges of the valve cusps are attached to chordae tendineae The heart valves (Fig. 7.5)
which are, in turn, attached below to papillary muscles. The latter are • The purpose of valves within the heart is to maintain unidirectional flow.
projections of muscle bundles on the ventricular wall. • The mitral (bicuspid) and tricuspid valves are flat. During ventricular
• The wall of the right ventricle is thicker than that of the atria but not systole the free edges of the cusps come into contact and eversion is
as thick as that of the left ventricle. The wall contains a mass of muscu- prevented by the pull of the chordae. Papillary muscle rupture can
lar bundles known as trabeculae carneae. One prominent bundle pro- occur as a complication of myocardial infarction. This is evident clin-
jects forwards from the interventricular septum to the anterior wall. ically by a pansystolic murmur representing regurgitant flow of blood
This is the moderator band (or septomarginal trabecula) and is of from ventricle to atrium.
importance in the conduction of impulses as it contains the right branch • The aortic and pulmonary valves are composed of three semilunar
of the atrioventricular bundle. cusps which are cup shaped. During ventricular diastole back-pressure
of blood above the cusps forces them to fill and hence close.

The heart I 21