Dr. Mujeeb Ahmed Shaikh Dr. Mohammed Sharique Ahmed Qaudri LARGE ITESTINE Dr. Mujeeb Ahmed Shaikh Dr. Mohammed Sharique Ahmed Qaudri

LARGE INTESTINE Large Intestine consist of Cecum, Appendix, Colon ascending colon, transverse colon and descending colon, end part of descending colon forms S shape sigmoid colon and straight part rectum.

Primarily a drying and storage organ Each day it receives about 500ml of chyme. The content received consist of Indigestible food residues (cellulose) Unabsorbed biliary components Remaining fluid Extracts more H2O and salt from the contents and the remains to be eliminated is known as feces Primary function of large intestine is to store feces.

LARGE INTESTINE We will discuss 1. Motility 2. Secretion 3. Digestion 4. Absorption

MOTILITY IN LARGE INTESTINE Haustral Contraction or Segmentation Mass movement [strong peristaltic waves]

Haustral Contraction [Segmentation Contraction] Initiated by the autonomous rhythmicity of colonic smooth muscle cells. They help to mix the contents of colon and expose contents to mucosa to facilitate absorption.

Haustral Contraction [Segmentation Contraction] They occur less frequently may be after every 30mins [they are like segmentation contraction in small intestine but in small intestine they occur 10-12/min]. Haustral contraction are largely controlled by locally mediated reflexes involving the intrinsic plexus.

Mass movement [strong peristaltic waves] They move the material from one portion of intestine to another. They occur 3-4 times per day, generally after meals and increase in motility moves the feces forward in few seconds. When material reaches the rectum, rectal distention initiates the defecation reflex.

Mass movement [strong peristaltic waves] Gastro-colic Reflex – when food enters the stomach, mass movements are triggered in the colon. It is mediated from stomach to the colon by gastrin and extrinsic autonomic nerves. It pushes the colonic contents into rectum triggering the defecation reflex.

SECRETION Large intestine secretes alkaline NaHCO3, mucus solution. Its function is to protect large intestine from mechanical and chemical injury. Mucus provides lubrication to facilitate the passage of feces.

DIGESTION There are no digestive enzymes secreted, therefore, no digestion takes place in large intestine. However, the colonic bacteria do digest some of the cellulose for their use.

The large intestine absorbs salt and water, converting the luminal contents into feces. The colon normally absorbs salt and H2O. Sodium is actively absorbed, Cl follows passively down the electrical gradient, and H2O follows osmotically. The colon absorbs token amounts of other electrolytes as well as vitamin K synthesized by colonic bacteria.

FECES About 500ml of material entering the colon per day from the small intestine, colon absorbs about 350ml, leaving 150g of feces to be eliminated per day. Feces contains 100g of water and 50g of solid [undigested cellulose, bilirubin [stercobilinogen], bacteria, unabsorbed food residue.

The colon contains myriad beneficial bacteria 500 to 1000 different species of bacteria typically live in the colon. Functions Enhance intestinal immunity promote colonic motility help maintain colonic mucosal integrity and make nutritional contributions. Promote absorption of calcium, magnesium, and zinc.

DEFECATION REFLEX Feces are eliminated by defecation reflex. How this reflex works? When mass movements of colon move the feces into the rectum. Distention of rectum initiates the reflex. Stretch receptors in the wall of rectum send impulses to the spinal cord ( S2,S3,S4), parasympathetic nerves causes contraction of smooth muscle of rectum and sigmoid colon and relaxation of internal sphincter.

DEFECATION REFLEX If external anal sphincter [which is skeletal muscle is also relaxed defecation occurs]. External anal sphincter is under voluntary control, therefore, can prevent defecation despite defecation reflex. When defecation occurs, it is assisted by voluntary straining movements that involve contraction of abdominal muscles and forceful expiration against closed glottis which increases intra-abdominal pressure.

CONSTIPATION When more water is absorbed from the feces, they become hard and dry. Normally frequency of passing stool vary. It maybe once a day, or after every meal or once every 2 or 3 days or once a week. CAUSES OF CONSTIPATION Ignoring the urge to defecate Decreased colonic motility due to low bulk diet, aging, emotion, anxiety. Colonic spasm, tumor in colon. Injury to nerve pathway.

INTESTINAL GAS OR FLATUS It is derived from two sources 1. Swallowed air [up to 500ml of air may be swallowed during a meal]. 2. Gas produced by bacterial fermentation in the colon. Most gas in the colon is due to result of bacterial activity, but the quantity and the nature of gas produced depend on the type of food eaten and colonic bacteria.

INTESTINAL GAS OR FLATUS Food such as beans, contain carbohydrate that human can not digest but can be attacked by gas producing bacteria. Gases produced are Hydrogen, Hydrogen Sulphide, Nitrogen, Carbon dioxide and Methane. Amount of gas per day passed is about 200ml. The smell is largely due to sulphides. Gas passing through the luminal contents give rise to gurgling sounds known as BORBORGYMI.

References Human physiology by Lauralee Sherwood, seventh edition Text book physiology by Guyton &Hall,11th edition Text book of physiology by Linda .s contanzo,third edition