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| | **This blood, carrying the products of digestion, enters the liver. | | **This blood, carrying the products of digestion, enters the liver. |
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| − | ==Histology==
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| − | [[Image:electronmicrographduodenum.jpg|thumb|right|150px|Electron Micrograph Duodenum - Copywright RVC 2008]]
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| − | [[Image:caudalduodenum.jpg|thumb|right|150px|Caudal Duodenum (cat) - Copywright 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 ane 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 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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| − | *'''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. Secrete peptides and amines.
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| − | **''paneth'' at the base of the crypt. Function unknown. Contain eosinophilic granules.
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| − | *'''Brunner's glands''' are present in the submucosa.
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| − | **Produce an alkaline secretion which neutralises stomach acid.
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| − | **Open into the crypts above in the mucosa.
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| − | *Lamina muscularis is smooth muscle.
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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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