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small, worm-shaped blind tube, about 3 in. (7.6 cm) long and 1-4 in. to 1 in. (.64–2.54 cm) thick, projecting from the cecum (part of the large intestine) on the right side of the lower abdominal cavity. The structure, also called the vermiform appendix, has no apparent function in people and has generally been considered a vestigial remnant of some previous organ or structure, having a digestive function, that became unnecessary to people in their evolutionary progress (see digestive systemdigestive system,
in the animal kingdom, a group of organs functioning in digestion and assimilation of food and elimination of wastes. Virtually all animals have a digestive system. In the vertebrates (phylum Chordata, subphylum Vertebrata) the digestive system is very complex.
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). It may, however, act as a source of healthy bacteria that can recolonize the intestines following severe diarrhea.

Infection of accumulated and hardened waste matter in the appendix may give rise to appendicitis, the symptoms of which are severe pain in the abdomen, nausea, vomiting, fever, abdominal tenderness, and muscle spasm. A blood count usually shows a rise in the number of white corpuscles. Appendicitis may occur at any age, although it is more prevalent in persons under 40 years of age. The danger in appendicitis is that the appendix can rupture, either spontaneously or because the patient has injudiciously been given laxatives or an enema, and that the infection can spread to the peritoneum (see peritonitisperitonitis
, acute or chronic inflammation of the peritoneum, the membrane that lines the abdominal cavity and surrounds the internal organs. It is caused by invasion of bacterial agents or irritant foreign matter during rupture of an internal organ, by spreading infection from
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). The risk of rupture is greater in older adults. Surgery, typically now performed laparoscopically, has been indicated historically in appendicitis, preceded and followed by antibiotic therapy, but recent studies have shown that in many cases uncomplicated appendicitis can be successfully treated with antibiotics alone.

The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a process of the cecum in lemurs, apes, humans, many rodents, and some Carnivora. The base of the human appendix is situated at the bottom of the cecum, 2–3 cm below the start of the ileum. The average length of the appendix in adults is 8–10 cm, and the cavity averages 4–5 mm in diameter. The appendix is not fixed and is sometimes found behind the peritoneum. It has its own mesentery with fatty tissue, blood vessels, nerves, and lymph nodes. Its wall consists of a mucous membrane and serous, muscular, and submucosal layers. The function and role of the appendix have been little-studied. Disorders of the appendix include appendicitis, diverticulosis, tumors, and, sometimes in humans, infestation by parasitic worms, protozoans, and fungi.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


Any appendage.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. a body of separate additional material at the end of a book, magazine, etc., esp one that is documentary or explanatory
2. Anatomy See vermiform appendix
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005