Colon

Article By:

Bock, Walter J. Department of Biological Sciences, Columbia University, New York, New York.

Last reviewed:August 2021

DOI:https://doi.org/10.1036/1097-8542.149200

The portion of the intestine that runs from the cecum to the rectum. The colon, also known as the large intestine or large bowel, is the final section of the digestive system and lies between the cecum and the rectum (see illustration). In some mammals, the colon may be separated from the small intestine by an ileocecal valve. The colon is usually divided into ascending, transverse, and descending portions. In humans, a fourth section, termed the sigmoid, is found. The colon is longer in herbivores and shorter in carnivores, and it measures about 1 to 2 m (3.3 to 6.6 ft) in length in humans. Although no digestive enzymes are secreted in the colon, digestion is assisted by an alkaline fluid. Much digestion (for example, all breakdown of cellulose) occurs by bacteria, of which Escherichia coli is the most common. Most of the fluid added to food during digestion is reabsorbed into the body in the colon. All digestive action, including water absorption, is completed before the food materials pass out of the colon into the rectum. See also: Digestive system; Escherichia; Intestine

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