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| − | <big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big>
| + | #REDIRECT[[:Category:Large Intestine - Anatomy & Physiology]] |
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| − | ==Introduction==
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| − | The large intestine extends from the [[Ileum - Anatomy & Physiology|ileum]] of the [[Small Intestine - Anatomy & Physiology|small intestine]] to the [[Anus - Anatomy & Physiology|anus]]. Water, electrolytes and nutrients are absorbed, concentrating the ingesta into faeces. Faeces are stored prior to defeacation. No chemical digestion takes place; there is no secretion of enzymes. All species have a large microbial population living in the large intestine, which is of particular importance to the [[Hindgut Fermenters - Anatomy & Physiology|hindgut fermenters]]. For this reason, hindgut fermenters have a more complex large intestine with highly specialised regions for fermentation.
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| − | The large intestine can be divided into:
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| − | *[[Caecum - Anatomy & Physiology|Caecum]]
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| − | *[[Colon - Anatomy & Physiology|Colon]]
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| − | *[[Rectum - Anatomy & Physiology|Rectum]]
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| − | *[[Anus - Anatomy & Physiology|Anus]]
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| − | ==Function==
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| − | '''Water Absorption'''
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| − | *Chyme entering the large intestine is semisolid. By the time chyme leaves the large intestine as faeces it is solid because most of the remaining water has been absorbed.
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| − | **Water absorption is achieved by the generation of an osmotic gradient between the gut lumen and the enterocytes. Sodium is actively transported into the enterocyte and is followed passively by chloride ions.
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| − | '''Vitamin Absorption'''
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| − | *The large intestine is colonised by a large quantity of bacteria that produce vitamins as a consequence of their own metabolism. The large intestine absorbs these vitamins, in addition to vitamins present in the diet.
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| − | '''Storage and Defecation'''
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| − | *Remaining water, waste and undigested food is stored as faeces prior to defecation. Defecation is the periodical expulsion of faeces into the environment.
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| − | ==Vasculature==
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| − | *The '''cranial mesenteric artery''' supplies the caecum, ascending and part of the transverse colon.
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| − | *The '''caudal mersenteric artery''' supplies the rest of the transverse colon, the descending colon and the rectum.
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| − | ==Innervation==
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| − | *Like the [[Small Intestine - Anatomy & Physiology|small intestine]], the large intestine recieves sympathetic and parasympathetic innervation.
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| − | *Neurones interact with the myenteric plexus to affect contractility, and with the submucosal plexus to affect secretions.
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| − | **The '''sympathetic '''have coeliac, cranial mesenteric and caudal mesenteric ganglia.
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| − | **As the sympathetic fibres leave the ganglia, they surround their respective artery.
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| − | **'''Parasympathetic''' innervation stimulates peristalsis.
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| − | ==Lymphatics==
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| − | [[Image:Colon fox lymphatic nodule.jpg|thumb|right|150px|Lymphatic Nodule - Copywright RVC 2008]]
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| − | *Lymphatic nodules are present in the mucosa.
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| − | ==Histology==
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| − | [[Image:mucosal layer of colon.jpg|thumb|right|150px|Mucosal Layer of Colon (Fox) - Copywright RVC 2008]]
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| − | *The mucosa of the large intestine is smooth; there are '''no villi or microvilli'''.
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| − | *Mucosal glands are much longer and straighter.
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| − | *The number of goblet cells in the mucosa is increased compared to the small intestine.
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| − | **Mucus is very important for lubrication of the ingesta as it passes through the intestine, particularly as more water is absorbed from the lumen making it drier.
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| − | *There are numerous scattered lymph nodules.
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| − | **The number of lymph nodules increases compared to the small intestine.
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| − | *The submucosa is much reduced in thickness.
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| − | *'''Taenia''' may be present.
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| − | **These are concentrations of the longitudinal muscle layer into long bands.
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| − | **When the taenia contract, they cause shortening of the large intestine, which produces saccualtions, or '''haustra'''.
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| − | *Many glands are present in the mucosa and skin of the anal region.
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| − | ==Species Differences==
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| − | ===Carnivore===
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| − | *The dog and cat posses two [[Anus - Anatomy & Physiology#Species Differnces|anal sacs]].
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| − | ===Ruminant===
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| − | ===[[Hindgut Fermenters - Horse - Anatomy & Physiology|Horse]]===
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| − | ===Pig===
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| − | *Taenia present
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| − | ==Links==
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| − | [[The Small and Large Intestines|Pathology of the Small and Large Intestine]]
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