Heart
The human heart is a specialized, have four chambered muscle that maintains blood flow in the circulatory system. The heart is located in the thorax, it lies on the left of the body's mid-line, above and in contact with the diaphragm. It is situated immediately behind the breastbone, or sternum, and between the lungs, with its apex titled to the left. 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 250 - 350 gram (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. Research indicates that the heart itself produces a hormonelike chemical. Brain cells are dependent on a constant oxygen supply, so death ensues shortly if a hear