SYSTEM. Located in the thorax, it lies left of the body's midline, above and in contact with the

diaphragm. It is situated immediately behind the breastbone, or sternum, and between the lungs, with its

apex tilted to the body cavity's left side. In most people the apex can be felt during each heart

contraction. At rest, the heart pumps about 59 cc (2 oz) of blood per beat and 5 l (5 qt) per minute,

compared to 120-220 cc (4-7.3 oz) per beat and 20-30 l (21-32 qt) per minute during exercise. The adult

human heart is about the size of a fist and weighs about 250-350 gm (9 oz).

Blood supplies food and oxygen to the cells of the body for their life needs and removes the waste

products of their chemical processes. It also helps to maintain a consistent body temperature, circulate

hormones, and fight infections. The brain cells are very dependent on a constant supply of oxygen. If the

circulation to the brain is stopped, death ensues shortly. Since heart attacks are the number-one cause

of death in the United States, the heart gets a great deal of attention.

The role of the heart was long considered a mystery and often given eleva

directly beneath the endocardium receive a sufficient amount of oxygen from the blood within the cavities

cells that emit regular impulses. Because of this spontaneous discharge of the sinus node, the heart

was the seat of the soul. Others thought it was the center of love, courage, joy, and sadness. Primitive

during rapid or pronounced cardiac action. The study of heart sounds and murmurs furnishes valuable

oxygen-rich blood in order to maintain their high metabolic rates and constant body temperature.

place: through the valves between the atria and the ventricles, which are now open again, blood is drawn

man must have been aware of the heartbeat and probably recognized the heart as an organ whose malfunction

tricuspid valve, which consists of three flaps, or cusps, of tissue. This valve directs blood flow from

The hearts of primitive vertebrates apparently had only one atrium and one ventricle. Since their body

resultant heart rate. In adults at rest this is between 60 and 74 beats a minute. In infants and young

overlying a thin layer of vascularized connective tissue. The outside of the heart, the epicardium, is in

and the lower pumping chambers are the thick-walled ven!

children it may be between 100 and 120 beats a minute. Tension, exertion, or fever may cause the rate of

rbon dioxide and receives oxygen, and then is returned to the heart's left side through four pulmonary

Some common words found in the essay are:
REGULATION HEARTBEAT, BLOOD HEART, HEART EXAMINATION, SYSTEM Located, HUMAN HEART, EVOLUTION HEART, CORONARY ARTERIES, heart muscle, , Motu Cordis, De Corde, atria ventricles, blood pumped, sa node, pulmonary artery, valves atria ventricles, heart's left, body temperature, muscle cells, blood flow, aortic valve, pulmonary artery aorta, blood pumped heart, contraction heart muscle, sound indicates closing,
Approximate Word count = 1823
Approximate Pages = 7 (250 words per page double spaced)