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Physiology Lecture 50

Physiology Lecture 50. Tanveer Raza MD MS MBBS razajju2@yahoo.com. ESOPHAGUS-STOMACH JUNCTION Longitudinal section. Tubular Glands Pyloric glands Secretes Mucus Gastrin Oxyntic Glands. Gastric Secretion. Tubular Glands Pyloric glands Oxyntic Glands Type of cells Mucous neck cells

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Physiology Lecture 50

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  1. Physiology Lecture 50 Tanveer Raza MD MS MBBS razajju2@yahoo.com

  2. ESOPHAGUS-STOMACH JUNCTIONLongitudinal section Tanveer Raza MD MS MBBS razajju2@yahoo.com

  3. Tubular Glands Pyloric glands Secretes Mucus Gastrin Oxyntic Glands Gastric Secretion Tanveer Raza MD MS MBBS razajju2@yahoo.com

  4. Tubular Glands Pyloric glands Oxyntic Glands Type of cells Mucous neck cells Mucus Peptic or Chief Cells Pepsinogen Parietal (or Oxyntic) cells Hydrochloric acid Intrinsic factor Gastric Secretion STOMACHFundus Tanveer Raza MD MS MBBS razajju2@yahoo.com

  5. Gastric Secretion:Mechanism of HCL secretion • pH=0.8 • (H+ concentration is 3 million times of arterial blood) • Concentration of 150-160 mEq/L Tanveer Raza MD MS MBBS razajju2@yahoo.com

  6. Gastric Secretion:Mechanism of HCL secretion Tanveer Raza MD MS MBBS razajju2@yahoo.com

  7. Gastric secretion:Postprandial Alkaline Tide • Postprandial alkaline tide • Postprandial increased gastric acid secretion results in more H+ being secreted • Raises pH of systemic blood • Urine becomes alkaline (Postprandial alkaline tide) Tanveer Raza MD MS MBBS razajju2@yahoo.com

  8. Gastric Secretion: HCl secretion • 3 stimulators of acid secretion in Parietal cells • Acetylcholine • via M3 muscarinic receptors, • Increases intracellular free Ca++ • Gastrin • Increases intracellular free Ca++ • Histamine • via H2 receptors, • Increases intracellular cAMP Tanveer Raza MD MS MBBS razajju2@yahoo.com

  9. Gastric Secretion: HCl secretion Tanveer Raza MD MS MBBS razajju2@yahoo.com

  10. Gastric Secretion: HCl secretion • Prostaglandin inhibits acid secretion by activating Gi Tanveer Raza MD MS MBBS razajju2@yahoo.com

  11. Enterochromaffin-like (ECL) cells • Neuroendocrine cells • Found in gastric mucosa • Synthesize and secrete • Histamine • Other peptide hormones Tanveer Raza MD MS MBBS razajju2@yahoo.com

  12. Enterochromaffin-like (ECL) cells • ECL secrete histamine in response to • Gastrin • Vagal stimulation • Acetylcholine • Other hormonal substance • Histamine secretion is inhibited by somatostatin Tanveer Raza MD MS MBBS razajju2@yahoo.com

  13. Enterochromaffin-like (ECL) cells HCl secretion by parietal cells is directly related to the amount of histamine secreted by ECL cells Tanveer Raza MD MS MBBS razajju2@yahoo.com

  14. Enterochromaffin-like (ECL) cells Food stimulates release of gastrin from antral G cells (G). Gastrin stimulates ECL cells to release histamine, which stimulates parietal cells (P) in the gastric corpus to secrete HCl. HCl stimulates release of somatostatin from somatostatin cells (S) in the antrum, inhibiting further gastrin release BMJ. 2001 October 27; 323(7319): 980–982 Tanveer Raza MD MS MBBS razajju2@yahoo.com

  15. Pepsinogen Gastric Secretion:Pepsinogen HCl Pepsin Proteolytic enzyme Pepsinogen Tanveer Raza MD MS MBBS razajju2@yahoo.com

  16. Intrinsic factor Essential for Vitamin B12 absorption in ileum Secreted by parietal cells If parietal cells are destroyed (Chronic gastritis) achlorhydria and pernicious anemia will develop Gastric Secretion: Intrinsic Factor Tanveer Raza MD MS MBBS razajju2@yahoo.com

  17. Hormonal Control of GI motility • Gastrin • Cholecystokinin  • Secretin  • Gastric inhibitory peptide  • Motilin Tanveer Raza MD MS MBBS razajju2@yahoo.com

  18. Hormonal Control of GI motility • Gastrin • Secreted by "G" cells of antrum of stomach  • Cause of secretion • Presence of food in stomach • Distention of the stomach • Products of proteins digestion • Gastrin releasing peptide • Function • Stimulation of gastric acid and pepsin secretion • Stimulation of growth of gastric mucosa Tanveer Raza MD MS MBBS razajju2@yahoo.com

  19. Hormonal Control of GI motility • Cholecystokinin  • Secreted by "I" cells in the mucosa of duodenum and jejunum  • Cause of secretion • Mainly in response to digestive products of fat, fatty acids, and monoglycerides in intestinal contents • Function • Strongly contracts gallbladder • Inhibits stomach contraction moderately Tanveer Raza MD MS MBBS razajju2@yahoo.com

  20. Hormonal Control of GI motility • Secretin  • Secreted by the "S" cells in the mucosa of the duodenum  • Cause of secretion • Acidic gastric juice emptying into duodenum from stomach • Function • Mild effect on GIT motility • Promotes pancreatic secretion of HCO3 Tanveer Raza MD MS MBBS razajju2@yahoo.com

  21. Hormonal Control of GI motility • Gastric inhibitory peptide  • Secreted by the mucosa of the upper small intestine • Cause of secretion • Fatty acids and amino acids but to a lesser extent in response to carbohydrate • Function • Mild effect in decreasing motor activity of the stomach Tanveer Raza MD MS MBBS razajju2@yahoo.com

  22. Hormonal Control of GI motility • Motilin • Secreted by the upper duodenum during fasting • Function • Increase GI motility Tanveer Raza MD MS MBBS razajju2@yahoo.com

  23. GI Blood Flow:Splanchnic Circulation • Blood from GIT, spleen and pancreas flow into liver by portal vein. After passing liver sinusoids, through hepatic veins drains into inferior vena cava Tanveer Raza MD MS MBBS razajju2@yahoo.com

  24. GI Blood Flow:Splanchnic Circulation • Reticuloendothelial (RE) cells lining liver sinusoids remove potentially harmful agents • Nonfat, water-soluble nutrients absorbed from GIT (such as carbohydrates & proteins) are absorbed and stored temporarily by RE cells and hepatic cells • Fat is absorbed by intestinal lymphatics, then to systemic circulation by thoracic duct, bypassing liver Tanveer Raza MD MS MBBS razajju2@yahoo.com

  25. GI Blood Flow:"Countercurrent" Blood Flow in Villi • Similar to vasa recta in renal medulla • Arterial & venous flow in opposite directions • Vessels lie in close apposition Tanveer Raza MD MS MBBS razajju2@yahoo.com

  26. GI Blood Flow:"Countercurrent" Blood Flow in Villi • Much of O2 diffuses out of arterioles directly into venules without being carried to the tips of the villi • Normal conditions: not harmful • Disease conditions when blood flow reduced: O2 deficiency can cause ischemia to the villus tip or the whole villus Tanveer Raza MD MS MBBS razajju2@yahoo.com

  27. GI Blood Flow: Nervous Control • Parasympathetic supply: • Increases local blood flow to stomach and lower colon • Sympathetic supply: • Intense vasoconstriction of GIT arterioles with greatly decreased blood flow Tanveer Raza MD MS MBBS razajju2@yahoo.com

  28. GI Blood Flow: Nervous Control • Parasympathetic supply • Sympathetic supply: • Importance • During heavy exercise, more flow to skeletal muscle & heart • In circulatory shock to body's vital tissues • In hemorrhagic shock to general circulation Tanveer Raza MD MS MBBS razajju2@yahoo.com

  29. GI Blood Flow: Autoregulatory Escape • After few minutes of vasoconstriction, flow often returns almost to normal by "autoregulatory escape" Sympathetic vasoconstriction Ischemia Local metabolic vasodilator Redilate the arterioles Tanveer Raza MD MS MBBS razajju2@yahoo.com

  30. Phases of Gastric Secretion • 3 "phases" • Cephalic • Gastric • Intestinal Tanveer Raza MD MS MBBS razajju2@yahoo.com

  31. Phases of Gastric Secretion • Cephalic Phase • Before food enters the stomach, especially while being eaten • 20% of the secretion • Gastric Phase  • Intestinal Phase Tanveer Raza MD MS MBBS razajju2@yahoo.com

  32. Phases of Gastric Secretion • Cephalic Phase • Gastric Phase  • Once food enters the stomach, • Due to • long vagovagal reflexes • local enteric reflexes • Gastrin • About 70% of total secretion • Intestinal Phase Tanveer Raza MD MS MBBS razajju2@yahoo.com

  33. Phases of Gastric Secretion • Cephalic Phase • Gastric Phase  • Intestinal Phase • Food in upper portion of small intestine Tanveer Raza MD MS MBBS razajju2@yahoo.com

  34. Thank You

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