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Large Intestine by Apex Energetics: Large Intestine 1 oz available acuatlanta.net | Shiatsu Large Intestine meridian Blended Learning at the Zen School of learn-shiatsu.co.uk | Digestive: Large Intestine/Colon conditions leessummitmedicalcenter.c... | Blood supply of the large intestine adam.about.com |
The large intestine is the second to last part of the digestive system—the final stage of the alimentary canal is the anus —in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body.[1] This article is primarily about the human gut, though the information about its processes are directly applicable to most mammals. The large intestine consists of the cecum and colon. It starts in the right iliac region of the pelvis, just at or below the right waist, where it is joined to the bottom end of the small intestine. From here it continues up the abdomen, then across the width of the abdominal cavity, and then it turns down, continuing to its endpoint at the anus. The large intestine is about 1.5 metres (4.9 ft) long, which is about one-fifth of the whole length of the intestinal canal.
[edit] Function and relation to other organsThe large intestine takes 32 hours to finish up the remaining processes of the digestive system. Food is not broken down any further in this stage of digestion. The large intestine simply absorbs vitamins that are created by the bacteria inhabiting the colon. It also absorbs water and compacts faeces, and stores faecal matter in the rectum until eliminated through the anus and thus is responsible for passing along solid waste. The term Large Intestine comes from the Latin term "Intestium Crassum" The large intestine differs most obviously from the small intestine in being wider and in showing the longitudinal layer of the muscularis have been reduced to 3 strap-like structures known as the taeniae coli. The wall of the large intestine is lined with simple columnar epithelium. Instead of having the evaginations of the small intestine (villi) the large intestine has invaginations (the intestinal glands). While both the small intestine and the large intestine have goblet cells, they are abundant in the large intestine. The vermiform appendix is attached to its posteromedial surface of the large intestine. It contains masses of lymphoid tissue. It is a part of mucosa-associated lymphoid tissue which gives the appendix an important role in immunity.[citation needed] Appendicitis is the result of a blockage that traps infectious material in the lumen. The appendix can be removed with no damage or consequence to the patient. The large intestine extends from the ileocecal junction to the anus and is about 1.5m long. On the surface, bands of longitudinal muscle fibers called taeniae coli, each about 5 mm wide, can be identified. There are three bands and they start at the base of the appendix and extend from the cecum to the rectum. Along the sides of the taeniae, tags of peritoneum filled with fat, called epiploic appendages (or appendices epiploicae) are found. The sacculations, called haustra, are characteristic features of the large intestine, and distinguish it from the small intestine. [edit] Bacterial floraMain article: Gut flora The large intestine houses over 700 species of bacteria that perform a variety of functions. The large intestine absorbs some of the products formed by the bacteria inhabiting this region. Undigested polysaccharides (fiber) are metabolized to short-chain fatty acids by bacteria in the large intestine and absorbed by passive diffusion. The bicarbonate the large intestine secretes helps to neutralise the increased acidity resulting from the formation of these fatty acids. These bacteria also produce large amounts of vitamins, especially vitamin K and Biotin (a B vitamin), for absorption into the blood. Although this source of vitamins generally provides only a small part of the daily requirement, it makes a significant contribution when dietary vitamin intake is low. An individual who depends on absorption of vitamins formed by bacteria in the large intestine may become vitamin deficient if treated with antibiotics that inhibit other species of bacteria as well as the disease-causing bacteria. Other bacterial products include gas (flatus), which is a mixture of nitrogen and carbon dioxide, with small amounts of the gases hydrogen, methane, and hydrogen sulphide. Bacterial fermentation of undigested polysaccharides produces these. The normal flora is also essential in the development of certain tissues, including the cecum and lymphatics. They are also involved in the production of cross-reactive antibodies. These are antibodies produced by the immune system against the normal flora, that are also effective against related pathogens, thereby preventing infection or invasion. The most prevalent bacteria are the bacteroides, which have been implicated in the initiation of colitis and colon cancer. Bifidobacteria are also abundant, and are often described as 'friendly bacteria'. A mucus layer protects the large intestine from attacks from colonic commensal bacteria.[2] This mucus layer is called the mucosal barrier. [edit] Parts and locationParts of the large intestine are:
Locations along the colon are:
[edit] In non-human animalsThe large intestine is only truly distinct in tetrapods, in which it is almost always separated from the small intestine by an ileocaecal valve. In most vertebrates, however, it is a relatively short structure running directly to the anus, although noticeably wider than the small intestine. Although the caecum is present in most amniotes, only in mammals does the remainder of the large intestine develop into a true colon.[3] In some small mammals, the colon is straight, as it is in other tetrapods, but in the majority of mammalian species it is divided into ascending and descending portions; a distinct transverse colon is typically only present in primates. Unusually, the taeniae coli and accompanying haustra are not found in either carnivorans or ruminants. The rectum of mammals (other than monotremes) is derived from the cloaca of other vertebrates, and is therefore not truly homologous with the "rectum" found in these species.[3] In fish, there is no true large intestine, but simply a short rectum connecting the end of the digestive part of the gut to the cloaca. In sharks this includes a rectal gland that secretes salt to help the animal maintain osmotic balance with the seawater. The gland somewhat resembles a caecum in structure, but is not a homologous structure.[3] [edit] References
[edit] External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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