Not to be confused with
sacrum.
The cecum or caecum (from the Latin caecus meaning blind) is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve (ICV) or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic junction.
Variation across species
A cecum is present in most amniote species, and also in lungfish, but not in any living species of amphibian. In reptiles, it is usually a single median structure, arising from the dorsal side of the large intestine. Birds typically have two paired ceca, as, unlike other mammals, do hyraxes.[1]
Most mammalian herbivores have a relatively large cecum, hosting a large number of bacteria, which aid in the enzymatic breakdown of plant materials such as cellulose; in many species, it is considerably wider than the colon. In contrast, obligatory carnivores, whose diets contain little or no plant material, have a reduced cecum, which is often partially or wholly replaced by the vermiform appendix.[1]
Many fish have a number of small outpocketings, called pyloric ceca, along their intestine; despite the name they are not homologous with the cecum of amniotes, and their purpose is to increase the overall area of the digestive epithelium.[1] Some invertebrates, such as squid,[2] may also have structures with the same name, but these have no relationship with those of vertebrates.
Etymology
The term cecum comes from the Latin caecum, literally "blind", here in the sense "blind gut" or "cul de sac".
In dissections by the Greek philosophers, the connection between the ileum of the small intestines and the cecum was not fully understood. Most of the studies of the digestive tract were done on animals and the results were compared to human structures.
The junction between the small intestine and the colon, called the ileocecal valve, is so small in some animals that it was not considered to be a connection between the small and large intestines. During a dissection, the colon could be traced from the rectum, to the sigmoid colon, through the descending, transverse, and ascending sections. The colon seemed to dead-end into the cecum, or cude-sac.
The connection between the end of the small intestine (ileum) and the start of the colon (cecum) is now clearly understood, but the name has not changed.
See also
Additional images
Location of McBurney's point (#1)
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The superior mesenteric artery and its branches.
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Arteries of cecum and vermiform process.
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Inferior ileocecal fossa.
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Interior of the cecum and lower end of ascending colon, showing colic valve.
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Topography of thoracic and abdominal viscera.
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References
- ^ a b c Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 353-354. ISBN 0-03-910284-X.
- ^ Williams, L.W. (1910), The anatomy of the common squid : Loligo pealii, Lesueur, American Museum Of Natural History
External links
