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Small Intestine gross anatomy:
- 3 parts:
- duodenum
- jejunum (2.5m)
- ileum (3.5m)
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duodenum:
- retroperitoneal
- shortest part (25 cm)
- C‑shaped, enclosing the head of the pancreas
- receives the bile and pancreatic ducts via the duodenal
- ampulla
-
jejunum (2.5m) and ileum (3.5m):
fan‑shaped mesentery (mesentery proper)
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blood supply and venous drainage to the small intestines:
- blood supply: mainly superior mesenteric artery from abdominal aorta
- venous drainage: superior mesenteric vein drains into the portal vein
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histology of the small intestine:
- plicae circulares ‑ permanent transverse folds
- mucosa:
- villi ‑ fingerlike projections
- simple columnar epithelium: mostly absorptive cells whose luminal surfaces bear microvilli (brush border) and between absorptive cells are goblet cells
- intestinal glands
- lamina propria: forms a core for each villus which contains blood capillaries and lymphatic capillaries
- (lacteals) - isolated aggregations of lymphatic tissue in jejunum which become more extensive in the ileum (Peyers' patches)
- submucosa:
- in the duodenum contains duodenal (Brunner's) glands that secrete alkaline mucus
-
intestinal glands (crypts of Lieberkuhn)
- between the bases of the villi:
- absorptive and goblet cells
- Paneth cells: produce lysozyme ‑ antibacterial
- enteroendocrine cells: produce cholecystokinin (CCK) and secretin
- stem cells
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Large Intestine:
- 3 parts:
- cecum:
- colon:
- rectum:
-
cecum:
- ileocecal valve
- vermiform appendix
-
colon:
- distinctive features: teniae coli, haustra, epiploic appendages
- ascending colon: retroperitoneal - right colic (hepatic) flexure
- transverse colon: transverse mesocolon - left colic (splenic) flexure
- descending colon: retroperitoneal
- sigmoid colon: sigmoid mesocolon
-
rectum:
- anal canal:
- anal columns
- internal and external anal sphincters
-
blood supply and venous drainage of the large intestine:
- blood supply:
- superior mesenteric artery- cecum, ascending and transverse colon
- inferior mesenteric artery- descending and sigmoid colon; rectum
- venous drainage: corresponding veins drain to the portal vein
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histology of the mucosa:
- no plicae circularis or villi
- simple columnar epithelium contains the same cells as small intestine
- goblet cells increase toward the anus
- in anal canal a change from simple columnar to stratified squamous epithelium
- intestinal glands (crypts) are deeper
- accumulations of lymphatic tissue in the lamina propria (and submucosa)
-
histology of the muscularis externa:
- in the cecum and colon, the outer longitudinal layer is in three longitudinal bands (teniae coli)
- in the anal canal, the circular muscle layer thickened as the internal anal sphincter
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