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Small Intestine - Anatomy & Physiology (view source)
Revision as of 07:45, 11 July 2008
, 07:45, 11 July 2008no edit summary
*In the pig, they form a long raised band in the middle of the mesentry.
*In the pig, they form a long raised band in the middle of the mesentry.
**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.
==Histology==
[[Image:electronmicrographduodenum.jpg|thumb|right|150px|Electron Micrograph Duodenum - Copywright RVC 2008]]
[[Image:caudalduodenum.jpg|thumb|right|150px|Caudal Duodenum (cat) - Copywright RVC 2008]]
*The mucosa is arranged into '''villi''' that provide a large surface area for absorption.
*Epithelium is simple columnar - ideal for absorption.
**Epithelial cells are known as enterocytes.
**A single layer of enterocytes overlies the lamina propria.
**Enterocytes originate from progenitor cells that migrate from mucosal crypts. They differentiate as they migrate up the villus.
**Enterocytes ane absorptive and posses microvilli.
*Membrane bound enzymes and transport proteins are also within the epithelium.
*Each villus houses capillaries that transport amino acids, monosaccharides and other digestive products and lacteals that transport triacylglycerides. Lacteals drain into the lymphatic system.
*'''Crypts''' are present at the base of each villus in the mucosa. Cell types in mucosal crypts (from luminal to basal):
**''goblet'' at the tip of the crypt. Produce mucous by exocytosis.
**''entero-endocrine'' in the middle of the crypt. Secrete peptides and amines.
**''paneth'' at the base of the crypt. Function unknown. Contain eosinophilic granules.
*'''Brunner's glands''' are present in the submucosa.
**Produce an alkaline secretion which neutralises stomach acid.
**Open into the crypts above in the mucosa.
*Lamina muscularis is smooth muscle.
**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.
==Species Differences==
==Species Differences==