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

temperature and metabolic rate fluctuated with the environmental temperature, they did not need as

heart muscle varies from 2 to about 20 mm (0.1 to 0.8 in). This thickness is correlated with the maximum

through the thoracic wall by the unaided ear, although they can be amplified by means of a STETHOSCOPE.

muscle cells of both atria and reaches the atrioventricular node (AV node), which lies on the border

the heart's left half is approximately twice as thick as that of the right half. The thickness of the

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

SIRENS a partial division takes place in the ventricle !

stimulus to the muscle cells of the heart's ventricles.

information regarding the condition of the heart muscle and valves. The heart sounds are recorded with

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

sends nerve branches to the heart. Through their stimulatory and inhibitory influences they determine the

Some topics in this essay:
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,