Anatomy of the Large Intestine CH 23 Anatomy of the Large Intestine James F. Thompson, Ph.D.

Large Intestine Functions Anatomy Completion of nutrient absorption, especially the final absorption of H2O Intestinal normal flora manufacture certain vitamins (B complex, K) Formation and expulsion of feces Anatomy 1.5 m L, 6.5 cm W Divided into 4 general areas: cecum colon rectum anal canal

Large Intestine: Anatomy Ileum to cecum - ileocecal sphincter cecum hangs below valve with appendix appendix vestigial Open end of cecum merges with a long tube, the colon (4 subdivisions): ascending transverse descending sigmoid

Large Intestine: Anatomy Rectum last 20 cm of GI tract, terminal 2-3 cm = anal canal rectal valves for flatus (gas) anal columns – stratified squamous epithelium anal sinuses – mucus secretion Anus external opening internal sphincter of smooth muscle (involuntary) external sphincter of skeletal muscle (voluntary)

Large Intestine Anatomy (cont.) Longitudinal smooth muscle reduced to bands: teniae coli Teniae coli contractions create pouches in the large intestine called haustra Circular smooth muscle contraction in the walls of the haustra compact the feces and assist in reabsorption of water and electrolytes

General Histology of GI Tract Same histological organization from inside to outside and from end to end

Large Intestine: Histology No villi or permanent circular folds in mucosa Long thin intestinal glands Columnar cells with microvilli for absortption Solitary lymphatic nodules

Large Intestine: Histology Muscularis mucosa Longitudinal and circular smooth muscle layers Longitudinal muscles reduced to longitudinal bands (teniae coli) which compress the large intestine into haustra (pouches) Serosal part of visceral peritoneum Small pouches of peritoneum Filled with fat (epiploic appendages) attached to teniae coli

Large Intestine: Histology

Colonoscopy diverticula fecaltih normal

Colon Polyps

End CH 23 Anatomy of the Large Intestine