The definitions used in this glossary of terminology either have been provided by the authors of the articles, or have been extracted wholly or in part, or paraphrased from the following sources: The American Medical Association Encyclopedia of Medicine, Charles B. Clayman, MD, Medical Editor, Random House, New York, 1989; Biotechnology from A to Z, 2d Edition, William Bains, Oxford University Press, New York, New York, 2002; A Dictionary of Genetics, 6th Edition, Robert C. King and William D. Stansfield, Oxford University Press, New York, New York, 2002; Dorland's Illustrated Medical Dictionary, 29th and 30th Editions, W. B. Saunders Company, Philadelphia, 2000, 2003; Genes VII, Benjamin Lewin, Oxford University Press, New York, New York, 2000; The Gale Encyclopedia of Genetic Disorders, Volumes I and II, Stacey L. Blachford, Ed., Thomson Learning, New York, New York, 2002; The Merriam-Webster Dictionary, Merriam-Webster, Inc., Springfield, Massachusetts, 1997; Molecular Biology of the Cell, 3rd Edition, Bruce Alberts, et al., Garland Publishing, 1994; The Random House Dictionary of the English Language, Unabridged Edition, 1966; Webster's Ninth New Collegiate Dictionary, 1991.

DEFINITION:

heart

The viscus of cardiac muscle that maintains the circulation of the blood. It is divided into four cavities-two atria and two ventricles. The left atrium receives oxygenated blood from the lungs. From there the blood passes to the left ventricle, which forces it via the aorta through the arteries to supply the tissues of the body. The right atrium receives the blood after it has passed through the tissues and given up much of its oxygen. The blood then passes to the right ventricle, and then to the lungs, to be oxygenated. The major valves are four in number: the left atrioventricular valve (mitral ), between the left atrium and ventricle; the right atrioventricular valve (tricuspid) , between the right atrium and ventricle; the aortic valve at the orifice of the aorta; and the pulmonary valve , at the orifice of the pulmonary trunk. The heart tissue itself is nourished by the blood in the coronary arteries.