Lecture 22: Large Intestine

Large Intestine

Role: Drying & Storage

Motility influences absorption

Haustral Contractions Overview

Haustral Contractions

Mass Movements

Propel colonic content

Mass movements occur 1 - 3 /day

High amplitude propagating contractions

Contents moved over a large distance in one movement

Typically start in cecum and sweep towards the rectum

Gastrocolic Reflex

Receptive Relaxation

Adaptive Relaxation

Internal Anal Sphincter relaxes via

NO and VIP

Hirschsprung’s Disease

Megacolon

Genetic M>F

Loss of ENS in distal part of colon

Involves the internal anal sphincter

Normal defecation reflex doesn’t occur → Fecal build

Symptoms: little to no bowel movement, abdominal distension, lethargic & vomiting

Tx: surgical removal of the aganglionic region (resection) restores the ability to defecate

Colonic secretion

Alkaline (HCO3- ) mucus solution

Absorption of short chain fatty acids

Ion Transport in Colon

Crohn’s and Ulcerative Colitis

Haustra are readily apparent radiologically and give the colon a lobed

appearance.

Loss of the haustra is a common observation in both Crohn's disease and chronic ulcerative colitis

The colon will have a symmetric, tubular appearance

The loss of haustration is associated with a loss of colonic motility

Crohn’s disease

Ulcerative Colitis

Hematochezia

Passage of blood through anus, bloody stools

Can result in hemorrhage

Diverticulosis and diverticulitis

Diverticulosis occurs when small, bulging pouches (diverticula) develop in the LI

Diverticulitis occurs when one or more of these pouches become inflamed or

infected

Diverticulosis

Diverticulitis