SMALL INTESTINE-I Motility ,Secretion and Digestion بسم الله الرحمن الرحيم SMALL INTESTINE-I Motility ,Secretion and Digestion Dr.Mohammed Sharique Ahmed Quadri Dr. Abdelrahman Mustafa Department of Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa Colleges

SMALL INTESTINE In small intestine MOST digestion and absorption takes place. Small intestine is divided into duodenum jejunum ileum.

SMALL INTESTINE ‘MOTILITY’ Motility in small intestine includes: 1. Segmentation 2. Migrating Motility Complex [MMC]

SMALL INTESTINE ‘MOTILITY’ Segmentation Definition oscillating, ring like contractions of smooth muscle. Description Contractile ring occur every few centimeter, dividing the small intestine into segments. Between the contracted segments are relaxed area containing small amount of Chyme. Segmentation occur about 12/min in duodenum and 9/min in terminal ileum. Contents take 3 to 5 hours to move through small intestine.

‘MOTILITY’ Initiation Interstitial cells of Cajal which produce Basic Electrical Rhythm [BER] or slow wave When BER reaches the threshold level in the circular smooth muscle segmentation are induced. Control Increased segmentation is caused by --local distension -gastrin secreted in stomach [gastro ileal reflex], - parasympathetic stimulation. Sympathetic stimulation decreases segmental activity. Functions – Mixing of food with digestive juices. Exposing all Chyme to small intestine mucosa for absorption. move(propelling) the food.

2. Migrating Motility Complex [MMC] INTESTINAL HOUSEKEEPER Defintion weak, repetitive peristaltic wave that move a short distance in the small intestine before dying out Description When most of the meals are absorbed, segmentation contraction stop and they are replaced by MMC in between the meals. MMC starts at the stomach and migrate down the intestine. MMC sweeps the intestine between meals.

Migrating Motility Complex [MMC] Function to move [sweep] the remaining contents of previous meal to the colon Initiation Interstitial cells of Cajal Control hormone motilin. Motilin hormone is secreted by endocrine cells of small intestinal mucosa.

Ileocecal Sphincter Ileum opens into the cecum. Ileocecal Sphincter prevents contamination of small intestine from chronic bacteria. Two factors contribute to this ileocecal valve: valve like folds of tissue protrude from ileum into the lumen of caecum Ileocecal sphincter smooth muscle in the wall of last several centimeter of ileum is thickened to form sphincter

Ileocecal Sphincter Pushing of Ileal contents forward in cecum causes Ileocecal valve to open . Ileocecal Sphincter [smooth muscle] is under neural [local myentric] and hormonal control. Distension on ileal side causes the sphincter to open ---reaction mediated by intrinsic plexus Gastrin release at onset of meal causes relaxation.

SMALL INTESTINE ‘SECRETION’ – Small intestinal secretion divided into TWO types 1)Succus entricus. 2) intestinal Enzymes

SMALL INTESTINE SECRETION Succus Entricus is secreted into the lumen by exocrine glands present in small intestine mucosa. It consist of: - Water - Mucus - Mineral Salts - pH 7.8 Secreted 1.5 liters per day. Secretion increases after meal due to local stimulation of small intestine mucosa by presence of Chyme.

SMALL INTESTINE SECRETION In the lumen surface of small intestine on the epithelial cells there are MicroVilli – hair like projection forming the brush border. What is brush border? It is plasma membrane and contains three types of enzyme: 1. Enterokinase – which activates pancreatic Proteolytic enzyme Trypsinogen.

SMALL INTESTINE SECRETION 2. Diasaccharidases – maltase, sucrase and lactase, which complete digestion of maltose, sucrose, and lactose into manosaccharides. 3. Amino pepti dases – which hydrolyze small peptides into amino acids, thereby completing protein digestion. Therefore, carbohydrate and protein digestion are completed in brush border.

SMALL INTESTINE ‘DIGESTION’ In small intestine, enzyme present in the brush border membrane complete the digestion. FAT: In the lumen of small intestine, pancreatic enzyme are acting for fat digestion, being held by bile, therefore, fats are completely reduced to absorble units of manocylecrides and free fatty acids.

SMALL INTESTINE ‘DIGESTION’ Protein: are broken down into peptide fragments and amino acids by trypsin and chymotrypsin. Carbohydrate: are reduced to diasaccharides and monosaccharides.

Applied Lactose Intolerance Occurs due to deficiency of lactase enzyme, therefore, digestion of lactose [milk and milk products] are not digested properly and lead to action of bacteria in the large intestine producing large quantity of CO2 and methane gas, distension of intestine, cramps and diarrhea.

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