anatomy, the intestine is the segment of the alimentary canal extending from the stomachto the anusand, in humans and other mammals, consists of two segments, the small intestineand the large intestine. In humans, the small intestine is further subdivided into the duodenum, jejunumand ileumwhile the large intestine is subdivided into the cecumand colon. [cite book
last = Maton
first = Anthea
coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright
title = Human Biology and Health
publisher = Prentice Hall
date = 1993
location = Englewood Cliffs, New Jersey, USA
isbn = 0-13-981176-1]
Structure and function
The structure and function can be described both as gross anatomy and at a microscopic level.
The intestinal tract can be broadly divided into two different parts, the small and large intestine. Grayish-purple in color and about 35 mm (1.5 inches) in diameter, the small intestine is the first and longest, measuring 6 to 7 meters (20-23 ft) long average in an adult man. Shorter and relatively stockier, the large intestine is a dark reddish color, measuring roughly 1.5 meters (5 ft) long on average.
The lumen is the cavity where digested material passes through and from where nutrients are absorbed. Both intestines share a general structure with the whole gut, and are composed of several layers. Going from inside the lumen radially outwards, one passes the mucosa (glandular epithelium and muscularis mucosa), submucosa, muscularis externa (made up of inner circular and outer longitudinal), and lastly serosa.
*Along the whole length of the gut in the
glandular epitheliumare goblet cells. These secrete mucuswhich lubricates the passage of food along and protects it from digestive enzymes. Villi are vaginations of the mucosa and increase the overall surface area of the intestine while also containing a lacteal, which is connected to the lymph system and aids in the removal of lipids and tissue fluid from the blood supply. Microvilli are present on the epithelium of a villus and further increase the surface area over which absorption can take place.
*The next layer is the muscularis mucosa which is a layer of smooth muscle that aids in the action of continued peristalsis along the gut. The submucosa contains nerves, blood vessels and elastic fibre with collagen that stretches with increased capacity but maintains the shape of the intestine.
*Surrounding this is the muscularis externa which comprises longitudinal and smooth muscle that again helps with continued peristalsis and the movement of digested material out of and along the gut.
*Lastly there is the serosa which is made up of loose connective tissue and coated in mucus so as to prevent friction damage from the intestine rubbing against other tissue. Holding all this in place are the mesenteries which suspend the intestine in the abdominal cavity and stop it being disturbed when a person is physically active.
The large intestine hosts several kinds of
bacteriathat deal with molecules the human body is not able to breakdown itself. This is an example of symbiosis. These bacteria also account for the production of gases inside our intestine (this gas is released as " flatulence" when eliminated through the anus). However the large intestine is mainly concerned with the absorption of water from digested material (which is regulated by the hypothalamus), the reabsorption of sodium, as well as any nutrients that may have escaped primary digestion in the ileum.
Gastroenteritisis inflammation of the intestines and is the most common disease of the intestines.
Ileusis a blockage of the intestines.
Ileitisis an inflammation of the ileum.
Colitisis an inflammation of the large intestine.
Appendicitisis inflammation of the vermiform appendixlocated at the caecum. This is a potentially fatal disease if left untreated; most cases of appendicitis require surgical intervention.
Coeliac diseaseis a common form of malabsorption, affecting up to 1% of people of northern European descent. Allergy to gluten proteins, found in wheat, barley and rye, causes villous atrophy in the small intestine. Life-long dietary avoidance of these foodstuffs in a gluten-free diet is the only treatment.
Crohn's diseaseand ulcerative colitisare examples of inflammatory bowel disease. While Crohn's can affect the entire gastrointestinal tract, ulcerative colitis is limited to the large intestine. Crohn's disease is widely regarded as an autoimmune disease. Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such. (See List of autoimmune diseases).
Enterovirusesare named by their transmission-route through the intestine ("enteric" = related to intestine), but their symptoms aren't mainly associated with the intestine.
Irritable bowel syndrome(IBS) is the most common functional disorder of the intestine. Functional constipation and chronic functional abdominal painare other disorders of the intestine that have physiological causes, but do not have identifiable structural, chemical, or infectious pathologies. They are aberrations of normal bowel function but not diseases.
Diverticular diseaseis a condition that is very common in older people in industrialized countries. It usually affects the large intestine but has been known to affect the small intestine as well. Diverticular disease occurs when pouches form on the intestinal wall. Once the pouches become inflamed it is known as Diverticulitis, (or Diverticular disease.)
Endometriosiscan affect the intestines, with similar symptoms to IBS.
Bowel twist(or similarly, bowel strangulation) is a comparatively rare event (usually developing sometime after major bowel surgery). It is, however, hard to diagnose correctly, and if left uncorrected can lead to bowel infarctionand death. (The singer Maurice Gibbis understood to have died from this.)
* [http://www.britannica.com/eb/article-9002491/intestine Encyclopædia Britannica article on intestine] retrieved on 2007-03-27
Inflammatory bowel disease(or "IBD")
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