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Small Intestine Overview - Anatomy & Physiology (view source)
Revision as of 17:58, 10 December 2010
, 17:58, 10 December 2010no edit summary
[[Image:Mlymph3.jpg|thumb|right|250px|Mesenteric lymph nodes (arrows) of rat- © Research Animal Diagnostic Laboratory]]
[[Image:Mlymph3.jpg|thumb|right|250px|Mesenteric lymph nodes (arrows) of rat- © Research Animal Diagnostic Laboratory]]
The products of fat digestion are transported in the lymph via the [[Lymphatic Vessels - Anatomy & Physiology|lymphatic vessels]], and when fat has been absorbed, it turns the lymph a milky colour. Lymph travels to the mesenteric lymph nodes and then through the efferent vessels that converge to form the cranial mesenteric trunk. The cranial mesenteric trunk drains into the '''chyle cistern'''. This is a dilation of the thoracic duct at its origin. It lies dorsally to the aorta and extends from the diaphragmatic crura to the renal arteries. Flow of lymph is facilitated by movement of the diaphragm in ventilation of the lungs and by pulsation of the aorta.
The products of fat digestion are transported in the lymph via the [[Lymphatic Vessels - Anatomy & Physiology|lymphatic vessels]], and when fat has been absorbed, it turns the lymph a milky colour. Lymph travels to the mesenteric lymph nodes and then through the efferent vessels that converge to form the cranial mesenteric trunk. The cranial mesenteric trunk drains into the '''chyle cistern'''. This is a dilation of the thoracic duct at its origin. It lies dorsally to the aorta and extends from the diaphragmatic crura to the renal arteries. Flow of lymph is facilitated by movement of the diaphragm in ventilation of the lungs and by pulsation of the aorta.
==Histology==
[[Image:electronmicrographduodenum.jpg|thumb|right|150px|Electron Micrograph Duodenum - © RVC 2008]]
[[Image:caudalduodenum.jpg|thumb|right|150px|Caudal Duodenum (cat) - © 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 are absorptive and posses microvilli.
*Membrane bound enzymes and transport proteins are also within the epithelium.
*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.
*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.
*'''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. Produce many important substances for the regulation of GIT motility. See Regulation & Control.
**''paneth'' at the base of the crypt. Function unknown. Contain eosinophilic granules.
*Lamina muscularis is smooth muscle.
*'''Brunner's glands''' are present in the submucosa of the '''duodenum'''.
**Secrete a protective mucous.
**Produce an alkaline secretion which neutralises stomach acid.
**Open into the crypts in the mucosa above.
**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.
*Submucosa is loose connective tissue and it contains blood vessels and nerve fibres.
*Tunica muscularis is smooth muscle.
**It consists of two muscle layers (see [[#Regulation & Control|regulation & control]]).
***An inner circular layer
***An outer longitudinal layer
*Serosa is loose connective tissue.
===Species Differences===
===Species Differences===
'''Test yourself with the [[Small Intestine - Anatomy & Physiology - Flashcards|Small Intestine Flashcards]]'''
'''Test yourself with the [[Small Intestine - Anatomy & Physiology - Flashcards|Small Intestine Flashcards]]'''
'''Click here for information on [[Peyer's Patches - Anatomy & Physiology|Peyer's Patches]]'''
'''Click here for information on [[Peyer's Patches - Anatomy & Physiology|Peyer's Patches]]'''