The human heart is a specialized, four-chambered muscle that maintains BLOOD flow in the CIRCULATORY.
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 elevated importance. Some thought it.
was the seat of the soul. Others thought it was the center of love, courage, joy, and sadness. Primitive.
man must have been aware of the heartbeat and probably recognized the heart as an organ whose malfunction.
could cause sudden death.
The Hippocratic De Corde, which probably dates from the time of ARISTOTLE, describes the construction of.
the heart's valves. LEONARDO DA VINCI made exquisite drawings of the heart, but it was not until the.
publication of William HARVEY's De Motu Cordis (1628) that the heart's specific role in relation to.
circulation was widely understood.
STRUCTURE AND FUNCTION OF THE HUMAN HEART.
The heart's wall has three parts. Muscle tissue, or myocardium, is the middle layer.