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Large Intestine
24.11--Large Intestine
Term | Definition |
---|---|
Large Intestine | Final portion of GI tract, 1.5m long. Cecum, colon, rectum, and anal canal |
Functions of Large Intestine | 1) Haustra Churning, peristalsis, and mass peristalsis 2) Bacteria contribute in breakdown of AAs 3) Some water, ions, and vit. absorption 4) Feces formed 5) Defecation |
Cecum | Inferior to ileocecal valve. Appendix is attached. Blood supply from superior and inferior mesenteric arteries. |
Appendix | Controls bacteria entering large intestine from lymphatic nodules; attached to ileum via mesoappendix |
Colon | Emerges from Cecum. Divides into ascending, transverse, descending and sigmoid. Ascending and descending are retroperitoneal. Blood suply from superior and inferior mesenteric arteries |
Rectum | Last 20cm of GI tract; anterior to sacrum and coccyx. |
Anal Canal | Stratified Squamous; Anal Columns contain network of arteries and veins |
Internal Anal Sphincter | Involuntary Smooth |
External Anal Spinchter | Voluntary Skeletal |
Superior and Inferior Mesenteric Veins | Venous return from veins goes to hepatic portal vein into liver. |
Rectal and Anal Canal Bloody Supply | Superior, Middle, and Inferior Rectal Arteries; Rectal Veins too |
Mucosa | Simple Columnar Epithelium; More Goblet cells than small intestine. Feature intestinal glands. Absorptive cells have microvilli |
Submucosa | Connective Tissue |
Muscularis | Longitudinal muscle is condensed and thickend forming bands--Teniae Coli. Contraction of Teniae Coli bands colon into Haustra |
Haustra | Result of contraction of Teniae Coli, gives large intestine puckered look |
Teniae Coli | Longitudinal muscle of Large intestine, condensed and thickened; feature omental appendices on Serosa |
Intestinal Glands | Not Villi, but ducts for secretion (gaps in between mucosa |
Haustral Churning | Haustra remain relaxed, fill up, then walls contract and push contents to next haustrum |
Mass Peristalsis | Strong peristaltic wave at middle of transverse colon to drive contents of colon into rectum |
Feces | Solidified, absorbed (dried out) chyme |
Defecation Reflec | Stimulation of stretch receptors by mass peristalsis which empties rectum |