Heart
The heart is a hollow, muscular organ which lies within the chest area between the lungs in a space called the mediastinum. It is slightly larger than a clenched fist and has the shape of a blunt cone. The weight of an average male heart is about 300 grams. Two-thirds of this mass lies to the left side of the body's midline.
There are four chambers in a human heart; the upper two chambers, at the
broadest end of the heart, are called the atria, while the lower two
chambers, at the apex end of the heart, are called the ventricles.
The heart possesses structures called valves analogous to doors which open in only one direction. The valves between the atria and ventricles are called atrioventricular valves (tricuspid on the right side; bicuspid, or mitral, on the left). The valve between the right ventricle and pulmonary artery is called the pulmonary valve; the valve between the left ventrical and ascending aorta is called the aortic valve. Two coronary arteries arise from the base of the aorta. They encircle and embrace the heart like a crown functioning to supply the heart tissue with oxygenated blood.
The heart functions to pump blood through a network of blood vessels. The atria receive blood, ventricles pump blood out to the periphery, and valves prevent back flow of the blood during contraction. Blood enters the right atrium from the superior and inferior vena cava. It is then pumped into the right ventricle through the tricuspid valve which closes to prevent back flow, allowing blood to flows into the pulmonary artery at which point the right semilunar valve closes. From the lungs, blood flows into the left atrium and is pumped through the mitral valve into the left ventricle. The ventricle contracts, shutting the mitral valve, and forcing the blood into the aorta which branches into the body. The left semilunar valve then shuts. The closing of the two atrioventricular valves produces the first heartbeat and the closing of the semilunar valves produces the second heartbeat.
References
Gray, H. 1977. Gray's Anatomy. Crown Publishers, Inc, New York. 1257 pp.
Van Amerongen, C. The Way Things Work; Book Of The Body. New York: Simon and Schuster, 1979.
| Signup Free Applied Health Journal |
||||
|
FREE Sample Issue Your email address is all we need to start you on a better path to health. We respect your privacy.
|
