The structure and function of the cardiovascular system: the heart

THE STRUCTURE AND FUNCTION OF THE CARDIOVASCULAR SYSTEM: THE HEART
The heart is a muscle approximately the size of a man's closed fist located within the chest cavity just left of center between the lungs. It is divided into two equal cavities separated by a wall of muscle: the "left" heart and the "right" heart; each half in turn is divided into two chambers: the upper one is called the atrium and a lower portion is known as the ventricle. A system of valves separates the atrias and ventricles and regulates the flow of blood into and out of the heart.
The structure of the heart can best be compared to a coupled double pump. As a matter of fact the left and right heart are two mechanically independent pumping stations that form a single organ. And like the heart, the circulatory system is also made up of two separate parts: pulmonary circulation serving the lungs, and the systemic circulation serving the body as a whole. The right heart pumps blood into the pulmonary circulation and the left heart supplies the systemic circulation. The division serves a vital function: the "exchange of gases" between air, blood, and tissues. As was previously mentioned, the body cells must be supplied with oxygen and be allowed to rid themselves of carbon dioxide in order to live. The supply and excretion of these two gases takes place in the following fashion. The right ventricle receives the deoxygenated blood from the vena cava and pumps it into the pulmonary circulation. The extensive capillary network promotes the rapid exchange between the air cells (alveoli) in the lungs and the deoxygenated blood pumped in by the heart; the red blood cells eliminate the carbon dioxide and take up oxygen. The oxygenated blood is then carried to the heart by the pulmonary vein, and then the heart sends it out into the blood stream.
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