spleen
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:
- spleen
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An organ that removes and destroys worn-out red blood cells and helps fight infection. Weighing about 7 ounces (200 grams), the spleen is a fist-sized, spongy, dark purple organ lying in the upper left abdomen behind the lower ribs.
STRUCTURE:
The spleen is covered with a capsule from which many fibrous bands run inward to give the organ a sponge-like structure. The spaces between the bands are filled with lymph tissue, composed of lymphocytes and phagocytes (cells that ingest other cells or foreign particles), and red blood cells. Blood is supplied to the spleen by a large artery that branches extensively within the organ.
FUNCTION:
One of the two main functions of the spleen is to control the quality of circulating red blood cells. It accomplishes this by removing and breaking down all worn-out red cells approximately 120 days after they have been produced in the bone marrow and by destroying other red cells that are misshapen or defective.
The other role of the spleen is to help fight infection by producing some of the antibodies, phagocytes, and lymphocytes that destroy invading microorganisms.
In the fetus, the spleen produces red blood cells. After birth, this function is taken over by the bone marrow. However, in certain diseases that affect cell production in the bone marrow (such as thalassemia), the spleen may resume production.
Despite its functions, the spleen is not an essential organ. If it is removed, its activities are largely taken over by other parts of the lymphatic system, although the individual is more susceptible to infection.
DISORDERS:
The spleen enlarges in many diseases, including infections such as malaria, infectious mononucleosis (glandular fever), schistosomiasis, tuberculosis, and typhoid fever; in leukemia and thalassemia; in some diseases that cause hemolytic anemia (such as sickle cell anemia); and in tumors of the spleen. The enlargement, which can often be felt as a swelling in the upper left abdomen, is sometimes accompanied by hypersplenism.
Lymphomas (tumors of lymphoid tissue) may develop in the spleen and elsewhere in the lymphatic system.
The spleen is sometimes ruptured by a severe blow to the abdomen, usually in an automobile crash or by a fall from a height. A rupture is much more likely if the spleen is enlarged or if overlying ribs are fractured. Rupture can cause severe bleeding, which may be fatal. For this reason, the injury requires an emergency operation to remove the spleen and tie off the artery supplying it.
Used in 2 Article bodies
Used in 2 Article bodies