Wednesday, February 3, 2010

BLOOD FLOW THROUGH THE HEART

BLOOD FLOW THROUGH THE HEART


Deoxygenated blood enters the right atrium from the superior vena cava, which brings blood from the head, thorax, and upper limbs, and from the inferior vena cava, which returns blood from the trunk, lower limbs, and abdominal viscera.
From the right atrium, the deoxygenated blood passes through the tricuspid valve into the right ventricle.
The right ventricle then contracts to pump the deoxygenated blood through the pulmonary valve into the right and left pulmonary arteries, which carry the oxygen-poor blood to the capillary network of the lungs. The pulmonary arteries are the only arteries in the body that carry deoxygenated blood. It is in the lungs where the exchange of gases takes place. Carbon dioxide leaves the bloodstream by way of the capillaries and passes into the alveoli of the lungs to be eliminated during respiration; oxygen passes from the alveoli of the lungs through the capillaries into the bloodstream, oxygenating the blood. This circulation of the blood from the heart to the lungs for oxygenation and back to the heart is known as pulmonary circulation.
The oxygenated blood is returned to the left atrium of the heart by way of four pulmonary veins (two from each lung). The pulmonary veins are the only veins in the body that carry oxygenated blood.
From the left atrium, the blood passes through the mitral, or bicuspid, valve into the left ventricle.
The left ventricle then pumps the blood through the aortic valve into the aorta.
The aorta branches into the arteries that distribute the freshly oxygenated blood to each body part and region.
This circulation of the blood from the heart to all parts of the body and back to the heart is known as systemic circulation

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