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1. LARGE INTESTINE 2. GIT HORMONES

LECTURE - 9 Dr. Zahoor Ali Shaikh. 1. LARGE INTESTINE 2. GIT HORMONES. Large Intestine consist of cecum, appendix, colon [ascending colon, transverse colon and descending colon, end part of descending colon forms sigmoid colon] and rectum.

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1. LARGE INTESTINE 2. GIT HORMONES

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  1. LECTURE - 9 Dr. Zahoor Ali Shaikh 1. LARGE INTESTINE 2. GIT HORMONES

  2. Large Intestine consist of cecum, appendix, colon [ascending colon, transverse colon and descending colon, end part of descending colon forms sigmoid colon] and rectum. Large Intestine does the function of water and electrolyte absorption and works as storage organ [primary function of large intestine is to store feces]. LARGE INTESTINE

  3. The colon normally receives 500ml of Chyme from the Small Intestine each day. • The contents coming to the colon consist of - Indigestible food residues e.g. cellulose, Unabsorbed Biliary components ,Fluid. • Colon absorbs water and salt, what remains behind is to be eliminated is know as feces. LARGE INTESTINE

  4. We will discuss 1. Motility 2. Secretion 3. Digestion 4. Absorption MOTILITY IN LARGE INTESTINE Haustral Contraction or Segmentation Peristaltic wave Mass movement [strong peristaltic waves] LARGE INTESTINE

  5. Haustral Contraction [Segmentation Contraction] • They help to mix the contents of colon and expose contents to mucosa to facilitate absorption. • 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. MOTILITY IN LARGE INTESTINE

  6. Peristaltic wave • They propel the contents towards the rectum. • 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. MOTILITY IN LARGE INTESTINE

  7. Mass movement [strong peristaltic waves] • Gastro-colic Reflex – when food enters the stomach, mass movements are triggered in the colon by gastro-colic reflex also. • 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. MOTILITY IN LARGE INTESTINE

  8. 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. LARGE INTESTINE

  9. DIGESTION • There are no digestive enzymes secreted, therefore, no digestion takes place in large intestine. LARGE INTESTINE

  10. ABSORPTION • Na+ is actively transported and water follows along the osmotic gradient. • Secretion of K+ and HCO3. • Due to absorptive capacity, some drugs are given per rectum especially in children e.g. anesthetics, steroids. • There are no villi in Large Intestine. LARGE INTESTINE

  11. 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. FECES

  12. They are commensals, which have no effect on host [they are not pathogen which cause disease]. Bacteria present are E.coli, bacteroides – fragilis. Some bacteria synthesize vitamin K, vitamin B-complex, folic acid. LARGE INTESTINE BACTERIA

  13. 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

  14. 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. DEFECATION REFLEX

  15. 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. DEFECATION REFLEX

  16. 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. CAUSES OF CONSTIPATION Decreased colonic motility due to low bulk diet, aging, emotion, anxiety. Colonic spasm, tumor in colon. Injury to nerve pathway. CONSTIPATION

  17. 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

  18. 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. INTESTINAL GAS OR FLATUS

  19. 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. INTESTINAL GAS OR FLATUS

  20. We will discuss the following hormones: • Gastrin • Secretin • CCK • Motilin • Somatostatin • GIP • VIP 2. OVERVIEW OF GASTRO-INTESTINAL HORMONES

  21. Produced by G-cells in the stomach. Stimulates the release of HCL and Pepsinogen in the stomach. Increases gastric motility. Increases ileal motility . Relaxes Ileocecal Sphincter. Induces mass movements in colon [because to help the contents moving through GIT on arrival of new meal in the stomach]. GASTRIN

  22. Secretin is released from small intestine when stomach acid contents come to duodenum. • Functions • It inhibits gastric emptying to delay the acid contents of stomach to enter in the duodenum. • It inhibits gastric secretion. • It acts on pancreatic duct to produce large volume of watery, NaHCO3 secretion. • It stimulates the secretion of NaHCO3 rich bile in the liver by acting on the bile ducts. SECRETIN

  23. CCK is released from the duodenum in response mainly to fat, to a lesser extent to protein products. CCK causes (i). Inhibition of Gastric motility and secretion (ii). Stimulates pancreatic Acinar cells to secrete pancreatic enzymes [amylase, lipase, Trypsinogen, Chymotrypsinogen]. (iii). It causes contraction of gall-bladder and relaxation of sphincter of Oddi. CCK [Cholecystokinin]

  24. It is polypeptide and secreted by entrochromaffin cells and Mo cells in the stomach, small intestine and colon. It causes contraction of smooth muscles in the stomach and intestine. Its level increases during inter-digestive state and controls GIT motility, Migrating motility complex (MMC) between the meals. MOTILIN

  25. It is secreted by D-Cells in pancreatic islets and by similar D-cells in GIT mucosa. Somatostatin inhibits secretion of Gastrin, VIP, GIP, Secretin and Motilin. Somatostatin secretion is stimulated by acid in the lumen of intestine. It acts probably in a paracrine fashion. SOMATOSTATIN

  26. GIP is released from the duodenum. GIP causes release of insulin. Insulin causes uptake and storage of glucose. GIP – before it was called Gastric Inhibitory Peptide [this role is minimum]. GIP [Glucose Dependent Insulinotorphic Peptide]

  27. VIP is found in nerves in the GIT. It stimulates intestinal secretion of electrolytes and water. Other action – relaxation of intestinal smooth muscle including sphincters. Inhibition of gastric acid secretion. It potentiates the action of acetylcholine in salivary glands. VIP is also found in brain, blood, autonomic nerves. VIP [Vasoactive Intestinal Peptide]

  28. REMINDER REGARDING GIT ENZYMES

  29. REMINDER REGARDING GIT ENZYMES

  30. REMINDER REGARDING ABSORPTION IN INTESTINE

  31. Large Intestine Motility, Secretion, Digestion, Absorption Feces Intestinal Bacteria Defecation Reflex Flatus Constipation GIT Hormones What You Should Know From This Lecture

  32. Thank you

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