I. Anatomic Features
II. Circulation of Blood

GLOSSARY
atherosclerosis same as atheroma, raised plaques filled with cholesterol, calcium, and other substances on the inner wall of arteries that obstruct the lumen and the flow of blood; the plaque of atheroma hardens the artery, hence the term atherosclerosis (sclerosis ¼ hardening).
capillaries minute, thin-walled blood vessels which connect the arterioles and the venules, forming a network in nearly all organs and tissues of the body.
coronary arteries the arteries that supply the heart muscle and other parts of the heart with blood.
heart the size of a closed fist, it lies within the chest cavity, directly under the breastbone (sternum); the shape of the heart is conical with the apex pointing downward to the left edge of the diaphragm.
myocardial infarction death of an area of heart muscle due to blockage of a coronary artery by blood clot and atheroma; medical term for a heart attack or coronary thrombosis.
myocardium the heart muscle.

A. Muscle Wall/Myocardium
The wall of the heart consists of three layers: (1) a middle layer of muscle fibers called the myocardium; (2) an outer thin covering, the pericardium (Fig. 2) and (3) an internal lining called the endocardium that is smooth as silk. The blood of the heart rests momentarily on the endocardium before it is ejected from the heart into the aorta.

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• I. ANATOMIC FEATURES
  Major structural parts of the heart include the muscular wall (myocardium), the inner lining (endothelium), the outer lining (pericardium), and the blood vessels supply¬ing the heart with blood. The coronary arteries and veins run along the surface of the heart through the pericardium and traverse the muscular wall. Anatomical features of the heart and circulation are illustrated in Figs. 1–10.
• II. CIRCULATION OF BLOOD A. The Heart is a Simple Pump
  The human heart is a muscular pump. Its function is to pump blood containing oxygen, glucose, protein, fat, and salts to every organ, tissue, and living cell of the body. The heart is divided into four chambers. The upper chambers are called the right and left atrium, and the lower chambers are called the right and left ventricles. Blood from all parts of the body drains into veins that empty into the right atrium. Blood passes from the right atrium through the tricuspid valve and reaches the right ventricle. During contraction of the right ventricle, blood is pushed into the lungs where it gives off CO2, takes up oxygen, and returns via the pulmonary veins to the left atrium (Fig. 4).
• BIBLIOGRAPHY
  Gaudin, A. J., and Jones, K. C. Human Anatomy and Physiology. Harcourt Brace Jovanovich, San Diego, 1989.

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