Essentials of Anatomy and Physiology

of the valve flaps and keeps the valve openings from

stretching. It also separates the myocardium of the

atria and ventricles and prevents the contraction of

the atria from reaching the ventricles except by way of

the normal conduction pathway.

As you can see from this description of the cham-

bers and their vessels, the heart is really a double, or

two-sided, pump. The right side of the heart receives

deoxygenated blood from the body and pumps it to

the lungs to pick up oxygen and release carbon diox-

ide. The left side of the heart receives oxygenated

blood from the lungs and pumps it to the body. Both

pumps work simultaneously; that is, both atria con-

tract together, followed by the contraction of both

ventricles. Aspects of the anatomy of the heart are

summarized in Table 12–1.

CORONARY VESSELS

The right and left coronary arteriesare the first

branches of the ascending aorta, just beyond the aortic

semilunar valve (Fig. 12–4). The two arteries branch

into smaller arteries and arterioles, then to capillaries.

The coronary capillaries merge to form coronary

The Heart 277

Pulmonary semilunar

valve

Aortic semilunar

valve Tricuspid

valve

Fibrous

skeleton

Bicuspid (mitral) valve

Posterior

Coronary artery

Figure 12–3. Heart valves in superior view. The atria
have been removed. The fibrous skeleton of the heart is
also shown.
QUESTION:When do the mitral and tricuspid valves
close, and why is this important?

Table 12–1 ANATOMY OF THE HEART

Structure Description

Epicardium

Myocardium

Endocardium

Right atrium (RA)

Tricuspid valve

Right ventricle (RV)

Pulmonary semilunar valve

Left atrium (LA)

Mitral valve

Left ventricle (LV)

Aortic semilunar valve

Papillary muscles and

chordae tendineae

Fibrous skeleton of the heart

Serous membrane on the surface of the myocardium

Heart muscle; forms the walls of the four chambers

Endothelium that lines the chambers and covers the valves; smooth to prevent abnor-

mal clotting

Receives deoxygenated blood from the body by way of the superior and inferior caval

veins

Right AV valve; prevents backflow of blood from the RV to the RA when the RV

contracts

Pumps blood to the lungs by way of the pulmonary artery

Prevents backflow of blood from the pulmonary artery to the RV when the RV relaxes

Receives oxygenated blood from the lungs by way of the four pulmonary veins

Left AV valve; prevents backflow of blood from the LV to the LA when the LV contracts

Pumps blood to the body by way of the aorta

Prevents backflow of blood from the aorta to the LV when the LV relaxes

In both the RV and LV; prevent inversion of the AV valves when the ventricles contract

Fibrous connective tissue that anchors the four heart valves, prevents enlargement of

the valve openings, and electrically insulates the ventricles from the atria