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Word Count: 1,837
HEARTThe human heart is a specialized four-chambered muscle that maintains BLOOD flow in the CIRCULATORYSYSTEM Located in the thorax it lies left of the bodys midline above and in contact with thediaphragm It is situated immediately behind the breastbone or sternum and between the lungs with itsapex tilted to the body cavitys left side In most people the apex can be felt during each heartcontraction At rest the heart pumps about 59 cc 2 oz of blood per beat and 5 l 5 qt per minutecompared to 120-220 cc 4-73 oz per beat and 20-30 l 21-32 qt per minute during exercise The adulthuman 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 wasteproducts of their chemical processes It also helps to maintain a consistent body temperature circulatehormones and fight infections The brain cells are very dependent on a constant supply of oxygen If thecirculation to the brain is stopped death ensues shortly Since heart attacks are the number-one causeof 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 itwas the seat of the soul Others thought it was the center of love courage joy and sadness Primitiveman must have been aware of the heartbeat and probably recognized the heart as an organ whose malfunctioncould cause sudden death The Hippocratic De Corde which probably dates from the time of ARISTOTLE describes the construction ofthe hearts valves LEONARDO DA VINCI made exquisite drawings of the heart but it was not until thepublication of William HARVEYs De Motu Cordis 1628 that the hearts specific role in relation tocirculation was widely understood STRUCTURE AND FUNCTION OF THE HUMAN HEARTThe hearts wall has three parts Muscle tissue or myocardium is the middle layer The
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