The document discusses gastrointestinal physiology, specifically colonic movements and the defecation reflex. It describes two types of colonic movements: segmentation movements that mix colonic contents, and propulsive movements that push stool towards the rectum. It explains that the defecation reflex is initiated when stool enters the rectum, causing contractions that push the stool out and relaxation of the anal sphincters to allow defecation.

1. Gastrointestinal physiology Transport & mixing of food (Cont). Dr.M.A.M.Shaikhani.

3. HAUSTRAL CONTRACTIONS Food residue Haustra

4. MASS MOVEMENTS Food residue Rectum

7. The Defecation Reflex Figure 24.25

8. Figure 24.25 Stretch receptors Sensory neurone Anal sphincters Parasympathetic neurone Somatic neurone DEFECATION REFLEX Rectum

9. Reflexes in the colon and rectum Mass movements + + Food in stomach Food in duodenum Faeces Defaecation reflex Colon rectum anus Ach Spinal cord IAS EAS FAECES + Distention - VIP ATP + - Pudendal nerve

10. The Defecation Reflex: Summary Removes undigested faeces from the body. Stretch receptors in GIT wall detect distension of rectum. Parasympathetic reflex causes contractions of the sigmoid colon & rectum + relaxation of internal anal sphincter. External anal sphincter (under voluntary control) consciously relaxed if appropriate.

11. Secretary functions of GIT: Of 2 types: 1.Enzymes helping digestion. 2.Mucous for lubrication & protection of GIT mucosal surfaces from excoriation. Anatomical types of secretary glands: 1.Mucous glands: 2 types: a.single cell (goblet cells). b.complex cell mucous glands. 2.Crypts of Liberkhan: deeper & contains specialized secretary cells. 3.Deep tubular glands in stomach & upper duodenum secreting acid & pepsinogen. 4.Complex glands like salivary ,pancreatic & hepatic glands.

15. CONTROL OF SALIVARY SECRETION cerebral cortex salivary centre in medulla autonomic nerves salivary glands  salivary secretion pressure receptors and chemoreceptors in the mouth other inputs:smell& taste centers conditioned reflex simple reflex

18. HCl Gastrin Histamine Pepsinogen

20. The Secretions of Hydrochloric Acid Figure 24.14

22. GASTRIN histamine Parietal cell ECL cell Chief cell D-cell somatostatin - + noradrenaline, CCK, VIP & CGRP Ach H + - + + Gland lumen + THE CONTROL OF ACID SECRETION

23. Acid inhibitory therapy H 2 receptor antagonists Histamine Parietal cell H 2 receptor H + /K + ATPase (the proton pump) H + K + Proton pump inhibitors Peptic ulcer reflux oesophagitis “heart burn” Tagamet, Zantac, Pepcid AC Omeprazole (Losec/Nexium) Gastrin: Proglumide Vagus: pirenzepine

26. 1. CEPHALIC PHASE Sight, smell or thought of food - Parasympathetic activation of gastric motility & gastric juice secretion Vagus nerve

27. Food arrival causes muscular reflexes & gastrin secretion by G cells. Gastrin stimulates secretion from both chief & parietal cells. 2. GASTRIC PHASE Gastrin GO FOOD

28. Arrival of food in duodenum triggers release of hormones that inhibit gastric motility & secretions. 3. INTESTINAL PHASE Circulation Secretin & Cholecystokinin (CCK)