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duodenum: (25 cm)
- retroperitoneal
- 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)
-
blood supply and venous drainage:
- mainly superior mesenteric artery from abdominal aorta
- superior mesenteric vein drains into the portal vein
-
mucosa:
- plicae circulares: permanent transverse folds
- epithelium: simple columnar epitheliummostly absorptive cells whose luminal surfaces bear microvilli (brush border)between absorptive cells are goblet cells
- intestinal glands (crypts of Lieberkuhn)‑ between the bases of the villi: absorptive and goblet cells
-
mucosa:
- 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
- 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
-
-
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:
- superior mesenteric artery: cecum, ascending and transverse colon
- inferior mesenteric artery: descending and sigmoid colon; rectum
- corresponding veins drain to the portal vein
-
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)
-
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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