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Small Intestine Overview - Anatomy & Physiology (view source)

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==Introduction==
 
==Introduction==
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====Development====
 
====Development====
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The small intestine develops from the digestive tube, which exists ventrally in the developing embryo. The digestive tube is endoderm, and therefore the small intestine and it's associated glands develop primarily from endoderm. Splanchnic mesoderm surrounds the digestive tube and gives rise to muscles of the tunica muscularis (for [http://en.wikipedia.org/wiki/Peristalsis| peristalsis]), blood vessels in the submucosa and connective tissue of the serosa.  
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The small intestine develops from the digestive tube, which exists ventrally in the developing embryo. The digestive tube is endoderm, and therefore the small intestine and it's associated glands develop primarily from endoderm. Splanchnic mesoderm surrounds the digestive tube and gives rise to muscles of the tunica muscularis (for peristalsis), blood vessels in the submucosa and connective tissue of the serosa.  
    
The intestines begin as a straight tube, suspended by the dorsal mesentry. The midgut and mesentry elongate to form a loop. The descending limb of the loop will form the [[Duodenum - Anatomy & Physiology|duodenum]], [[Jejunum - Anatomy & Physiology|jejunum]] and [[Ileum - Anatomy & Physiology|ileum]]. The ascending limb will form the terminal portion of the [[Ileum - Anatomy & Physiology|ileum]], [[Caecum - Anatomy & Physiology|caecum]] and first half of the [[Colon - Anatomy & Physiology|colon]]. The midgut loop rotates about the cranial mesenteric artery in a clockwise direction (when viewed dorsoventrally). It undergoes a 270° rotation so that the [[Caecum - Anatomy & Physiology|caecum]] and ascending [[Colon - Anatomy & Physiology|colon]] ends up on the right, and the small intestine ends up on the left.
 
The intestines begin as a straight tube, suspended by the dorsal mesentry. The midgut and mesentry elongate to form a loop. The descending limb of the loop will form the [[Duodenum - Anatomy & Physiology|duodenum]], [[Jejunum - Anatomy & Physiology|jejunum]] and [[Ileum - Anatomy & Physiology|ileum]]. The ascending limb will form the terminal portion of the [[Ileum - Anatomy & Physiology|ileum]], [[Caecum - Anatomy & Physiology|caecum]] and first half of the [[Colon - Anatomy & Physiology|colon]]. The midgut loop rotates about the cranial mesenteric artery in a clockwise direction (when viewed dorsoventrally). It undergoes a 270° rotation so that the [[Caecum - Anatomy & Physiology|caecum]] and ascending [[Colon - Anatomy & Physiology|colon]] ends up on the right, and the small intestine ends up on the left.
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===Bovine===
 
===Bovine===
 
Up to 50m.
 
Up to 50m.
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==Histology==
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[[Image:electronmicrographduodenum.jpg|thumb|right|150px|Electron Micrograph Duodenum - © RVC 2008]]
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[[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.
    
==Links==
 
==Links==
    
'''Test yourself with the [[Small Intestine - Anatomy & Physiology - Flashcards|Small Intestine  Flashcards]]'''
 
'''Test yourself with the [[Small Intestine - Anatomy & Physiology - Flashcards|Small Intestine  Flashcards]]'''
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'''Click here for information on [[Small Intestine - Histology|histology]]'''
      
'''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]]'''
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'''Click here for information on [[Intestines, Small and Large - Pathology|Pathology of the Small and Large Intestines]]'''
 
'''Click here for information on [[Intestines, Small and Large - Pathology|Pathology of the Small and Large Intestines]]'''
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'''Click here for information on [[Equine Alimentary System  - Anatomy & Physiology| The Horse's Small Intestine]]'''
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'''Click here for information on [[Alimentary System  - Horse Anatomy#Small Intestine| The Horse's Small Intestine]]'''
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'''Video links:'''
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[http://stream2.rvc.ac.uk/Anatomy/bovine/Pot0048.mp4 Pot 48 The Small and Large intestine of the Ruminant]
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[http://stream2.rvc.ac.uk/Anatomy/canine/Pot0036.mp4 Pot 36 The Canine Abdomen]
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[http://stream2.rvc.ac.uk/Anatomy/equine/Pony_abdomen.mp4 Lateral View of the Equine Abdomen]
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[http://stream2.rvc.ac.uk/Frean/Pony/left_topography.mp4 Left Sided topography of the Equine abdomen]
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[http://stream2.rvc.ac.uk/Frean/Pony/right_topography.mp4 Right sided topography of the Equine Abdomen]
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{{Template:Learning
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|videos = [[Video: Ruminant small and large intestine potcast|Ruminant small and large intestine potcast]]<br>[[Video: Ruminant abdomen potcast|Ruminant abdomen potcast]]<br>[[Video: Foal gastrointestinal tract potcast|Foal gastrointestinal tract potcast]]<br>[[Video: Lateral view of the feline thorax and abdomen potcast|Lateral view of the feline thorax and abdomen potcast]]<br>[[Video: Female dog abdomen dissection|Female dog abdomen dissection]]<br>[[Video: Abdominal viscera of the horse dissection|Abdominal viscera of the horse dissection]]<br>[[Video: Equine left-sided abdominal and thoracic topography dissection|Equine left-sided abdominal and thoracic topography dissection]]<br>[[Video: Equine left-sided abdominal and thoracic topography dissection 2|Equine left-sided abdominal and thoracic topography dissection 2]]<br>[[Video: Ovine large and small intestine dissection|Ovine large and small intestine dissection]]<br>[[Video: Porcine abdomen dissection|Porcine abdomen dissection]]
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|Vetstream = [https://www.vetstream.com/canis/search?s=intestine Intestinal diseases and Surgery]
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}}
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[http://stream2.rvc.ac.uk/Anatomy/feline/pot0357.mp4 Pot 357 The Feline Abdomen]
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[http://stream2.rvc.ac.uk/Frean/sheep/LargeSmallIntestine.mp4 Small and Large intestine of the Sheep]
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[http://stream2.rvc.ac.uk/Frean/sheep/RightSideTopography.mp4 Right sided topography of the Ovine Abdomen]
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[http://stream2.rvc.ac.uk/Anatomy/swine/Pig_abdomen.mp4 The Porcine Abdomen]
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==Webinars==
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<rss max="10" highlight="none">https://www.thewebinarvet.com/gastroenterology-and-nutrition/webinars/feed</rss>
    
[[Category:Small Intestine - Anatomy & Physiology]]
 
[[Category:Small Intestine - Anatomy & Physiology]]
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[[Category:To Do - AimeeHicks]][[Category:To Do - Review]]
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[[Category:To Do - AimeeHicks]]
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