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| − | {{toplink
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| − | |backcolour =BCED91
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| − | |linkpage =Alimentary - Anatomy & Physiology
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| − | |linktext =Alimentary System
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| − | <br>
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| | ==Introduction== | | ==Introduction== |
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| | **They are routinely examined after slaughter as enlargement indicates enteric disease or tuberculosis. | | **They are routinely examined after slaughter as enlargement indicates enteric disease or tuberculosis. |
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| − | ==Histology== | + | ==[[Small Intestine - Histology|Histology]]== |
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| − | [[Image:electronmicrographduodenum.jpg|thumb|right|150px|Electron Micrograph Duodenum - © RVC 2008]] | |
| − | [[Image:caudalduodenum.jpg|thumb|right|150px|Caudal Duodenum (cat) - © RVC 2008]]
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| − | *The mucosa is arranged into '''villi''' that provide a large surface area for absorption.
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| − | *Epithelium is simple columnar - ideal for absorption.
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| − | **Epithelial cells are known as '''enterocytes'''.
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| − | **A single layer of enterocytes overlies the lamina propria.
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| − | **Enterocytes originate from progenitor cells that migrate from mucosal crypts. They differentiate as they migrate up the villus.
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| − | **Enterocytes are absorptive and posses microvilli.
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| − | *Membrane bound enzymes and transport proteins are also within the epithelium.
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| − | *Each villus houses a generous blood supply of capillaries that transport amino acids, monosaccharides and other digestive products and lacteals that transport triacylglycerides. Lacteals drain into the lymphatic system.
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| − | *Two types of secretion are produced in the small intestine; together they are called the ''succus entericus''. The first type of secretion is from the crypts, the second is from the Brunner's glands.
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| − | *'''Crypts''' are present at the base of each villus in the mucosa. Cell types in mucosal crypts (from luminal to basal):
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| − | **''goblet'' at the tip of the crypt. Produce mucous by exocytosis.
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| − | **''entero-endocrine'' in the middle of the crypt. Produce many important substances for the regulation of GIT motility. See Regulation & Control.
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| − | **''paneth'' at the base of the crypt. Function unknown. Contain eosinophilic granules.
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| − | *Lamina muscularis is smooth muscle.
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| − | *'''Brunner's glands''' are present in the submucosa of the '''duodenum'''.
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| − | **Secrete a protective mucous.
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| − | **Produce an alkaline secretion which neutralises stomach acid.
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| − | **Open into the crypts in the mucosa above.
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| − | **Contraction of smooth muscle shortens the villus. This helps to pump out absorbed products of digestion. Relaxation of smooth muscle lengthens the villus which increases surface area, facilitating absorption.
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| − | *Submucosa is loose connective tissue and it contains blood vessels and nerve fibres.
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| − | *Tunica muscularis is smooth muscle.
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| − | **It consists of two muscle layers (see [[#Regulation & Control|regulation & control]]).
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| − | ***An inner circular layer
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| − | ***An outer longitudinal layer
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| − | *Serosa is loose connective tissue.
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| | ==Species Differences== | | ==Species Differences== |