3 a gastric secretion and its regulation

HCL, mucus and pepsin secretions

1. Gastric Secretion and Its Regulation Part I

2. Learning Objectives Stomach: Parts, Function and Gastric Glands Gastric Secretions Regulation Phases Of Secretion

3. M ost dilated part Bag like organ Lies in epigastric , umblical & left hypogastric regions of the abdomen

4. Functions of stomach Temporary storage of food Grinding & mixing of food Secretion of HCl Secretion of intrinsic factor (IF) Secretion of pepsinogen Absorption of water and lipid soluble substances Performs its own controlled emptying

5. Surface/Neck mucous cells- secrete protective bicarbonate ions Parietal   Cells- most numerous in the  isthmus  of the glands, secrete gastric acid (HCL) +   intrinsic factor . Structure of Glands Chief / peptic / zymogenic cells- located towards the bases of the gastric glands. Secrete gastric lipase and pepsinogen .

6. Neuroendocrine cells- part of the diffuse neuroendocrine system, secrete serotonin and other hormones Stem cells- divide continuously to replace all other types of cell in the glands.

7. Synthesize and secrete the HCl acid responsible for the acidic pH in the gastric lumen. Synthesize and secrete the protease precursor known as pepsinogen. Produce alkaline mucus that covers mucosa layer

8. Contents of Normal Gastric Juice Vol ume: 1 -1.5 liters Nature: acidic pH 0.7 to 4 Constituents : Water (99.5%); solids (0.5%) Inorganic constituents: anions ( Cl - , PO 4 3- , SO 4 2- & HCO 3 - and cations (H + , Na + , K + , Ca ++ , Mg ++ ) Organic constituents: pepsinogen, IF, mucin , renin, gastric lipase, gelatinase , carbonic anhydrase and lysozyme.

9. Structure of parietal cell: resting and stimulated H + - K + ATPase in inactive form When activated , fuse to cell membrane & microvilli project to increase surface area for secretion

10. Mechanism of HCl Secretion Water dissociated into H + & OH - Pumping of H + out of cell by H + K + ATPase ; permits OH - to accumulate & form HCO 3 - from CO 2 Water passes into canaliculus by osmosis making gastric juice isotonic to plasma

11. Postprandial Alkaline Tide

12. Pyloric gland Oxyntic gland

13. Regulation of HCl Secretion

14. Pyloric gland Oxyntic gland Potentiation

15. Agents stimulating the parietal cells Ach Gastrin Histamine Agents inhibiting the parietal cells Acid Somatostatin

16. Meal Related Phases of Gastric Secretion Cephalic phase : 30% Gastric phase: 60% Intestinal phase: 10%

17. sight, aroma, taste, thought Cephalic phase

18. Sham feeding

19. Gastric phase

20. Intestinal phase

21. Inter-digestive phase

22. Other influences Hypoglycemia: acts via brain and vagal efferent – stimulate acid and pepsin secretion Alcohol: moderate amount of alcohol – increase gastric secretion

23. Enteric hormones that inhibit gastric H + secretion

24. Pepsinogen secretion Secreted by chief cells in gastric glands, & mucous cells Pepsinogen : aspartic proteinases , endopeptidases Two types: Group I ( chief cells of corpus) group II ( chief cells + mucous neck cells in all parts) Zymogen granule compound exocytosis pepsinogen

25. Agonist acting through Ca ++ M3 muscarinic receptors for Ach Gastrin/ CCk family peptides’ receptors S timulated by:

26. Regulation of Pepsinogen Secretion

27. Mucus Secreted by : Surface mucous cells Mucous neck cells Glandular mucous cells forms a mucus gel layer with PLs, electrolytes , water

28. Mucus Secretion & its Regulation V agal stimulation and irritation stimulate gastric mucous cells to secrete mucin Gastric surface cells secrete HCO 3 - , stimulated by Ach, Acids & PGs . Entry of acid into the duodenum induces S ecretin from S cells triggering HCO 3 - secretion by pancreas/duodenum & neutralizes Gastric acid

29. Mucus protects the gastric surface epithelium by trapping an HCO 3 - rich fluid near the apical border of these cells

30. Gastric mucosal barrier Mucus Bicarbonates Epithelium- tight junctions+ surface membranes Prostaglandins Trefoil peptides

31. What we learned today…. Stomach: Parts, Function and Gastric Glands Gastric Secretions Regulation Phases Of Secretion

32. Structure of Gastric Glands and secretions

33. Mechanisms sight, aroma, taste, thought -----> hypothalamus gustatory centers -----> vagal nuclei of medulla -----> vagus nerve (parasympathetic) -----> increased gastric secretion