Vermiform appendix
From Wikipedia, the free encyclopedia
Vermiform Appendix | |
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Arteries of cecum and vermiform appendix. (Appendix visible at lower right, labeled as "vermiform process"). | |
Normal location of the appendix relative to other organs of the digestive system (anterior view). | |
Latin | dixermiformis |
Gray's | subject #942 8711 |
System | Digestive |
Precursor | Midgut |
MeSH | Appendix |
Dorlands/Elsevier | a_54/12147735 |
In human anatomy, the vermiform appendix (or appendix, pl. appendices) is a blind ended tube connected to the cecum. It develops embryologically from the cecum. The term "vermiform" comes from Latin and means "wormlike in appearance". The cecum is the first pouch-like structure of the colon. The appendix is near the junction of the small intestines and large intestines.
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[edit] Size and location
The appendix averages 100 mm in length, but can range from 20 to 200 mm. The diameter of the appendix is usually less than 7 to 8 mm. The longest appendix ever removed was that of a Pakistani man on June 11, 2003, at Pakistan Institute of Medical Sciences, Islamabad, measuring 235 mm (9.2 in) in length. [1]
While the base of the appendix is at a fairly constant location, the location of the tip of the appendix can vary from being retrocaecal to being in the pelvis to being extraperitoneal. In most people, the appendix is located at the lower right quadrant of the abdomen. In people with situs inversus, the appendix may be located in the lower left side.
[edit] Function
Medical literature shows that the appendix is not generally credited with significant function. The appendix is rich in infection-fighting lymphoid cells, suggesting that it might play a role in the immune system.[citation needed] Whether the appendix has a function or not, it can be removed without any ill effects or side effects.
There have been cases of people who have been found, usually on laparoscopy or laparotomy, to have a congenital absence of their appendix. There have been no reports of impaired immune or gastrointestinal function in these people.
The most common explanation is that the appendix is a vestigial structure with no absolute purpose. In The Story of Evolution Joseph McCabe argued thus:
The vermiform appendage—in which some recent medical writers have vainly endeavoured to find a utility—is the shrunken remainder of a large and normal intestine of a remote ancestor. This interpretation of it would stand even if it were found to have a certain use in the human body. Vestigial organs are sometimes pressed into a secondary use when their original function has been lost.
The appendix is thought to have descended from an organ in our distant herbivorous ancestors called the cecum (or cæcum). The cecum is maintained in modern herbivores, where it houses the bacteria that digest cellulose, a chemically tough carbohydrate that these animals could not otherwise utilize. The human appendix contains no significant number of these bacteria, and cellulose is indigestible to humans. It seems likely that the appendix lost this function before human ancestors became recognizably human.
Loren G. Martin[3], argues that the appendix has a function in fetuses and adults. Endocrine cells have been found in the appendix of 11 week of fetuses that contribute to "biological control (homeostatic) mechanisms." In adults, Martin argues that the appendix acts as a lymphatic organ.
[edit] See also
[edit] Diseases
The most common diseases of the appendix (in humans) are appendicitis and carcinoid tumors.
Appendix cancer accounts for about 1 in 200 of all gastrointestinal malignancies.
An operation to remove the appendix is an appendicectomy (also appendectomy).
[edit] Additional images
[edit] References
- ^ Guinness world record for longest appendix removed.
- ^ Fisher, R. E. (2000) "The primate appendix: a reassessment." Anat Rec. 261: 228-236. PubMed
- ^ A professor of physiology claims the appendix has a known function
[edit] External links
- "The vestigiality of the human vermiform appendix: A Modern Reappraisal" -- evolutionary biology argument that the appendix is vestigial
- SUNY Labs 37:12-0102 - "Abdominal Cavity: The Cecum and the Vermiform Appendix"
Anatomy of torso, digestive system: Gastrointestinal tract |
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Upper gastrointestinal tract Mouth • Pharynx (nasopharynx, oropharynx, hypopharynx) • Esophagus • Crop • Stomach (rugae, gastric pits, cardia/gland, fundus/gland, pylorus/gland, pyloric antrum) Lower gastrointestinal tract Large intestine: Cecum • Colon (ascending colon, transverse colon, descending colon, sigmoid colon) • Rectum (Houston valve, rectal ampulla, pectinate line) • Anal canal (anal valves, anal sinuses, anal columns) Anus: Sphincter ani internus muscle • Sphincter ani externus muscle GALT: Peyer's patches • M cells intestinal villus • crypts of Lieberkühn • circular folds • taenia coli • haustra • epiploic appendix |