Heyworth, Martin AIDS Research Center, Veterans Administration Medical Center, San Francisco, California.
Last reviewed:April 2021
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The passage of loose or watery stools, usually at more frequent than normal intervals. Diarrhea is characterized by more-frequent and abnormally loose or watery stools (greater than 227 g or 8 oz per 24 h). The two principal mechanisms responsible for diarrhea are (1) the rise in osmotic pressure of fecal contents, diminishing the absorption of water by the intestine (osmotic diarrhea); and (2) the increase in electrolyte secretion into the intestinal lumen by its epithelial cells, leading to an increased flow of water from the intestinal mucosa into the lumen (secretory diarrhea). The causes of diarrhea are varied. Often, diarrhea results from bacterial, viral, parasitic, and protozoan infections (see illustration). See also: Digestive system; Gastrointestinal tract disorders; Intestine
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