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Semelhante a 3 a gastric secretion and its regulation
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3 a gastric secretion and its regulation
- 3. Learning Objectives •Stomach: Parts, Function and Gastric Glands •Gastric Secretions •Regulation •Phases Of Secretion
- 4. Most dilated part Bag like organ Lies in epigastric, umblical & left hypogastric regions of the abdomen
- 5. 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
- 8. • 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.
- 9. • 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.
- 10. 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
- 11. Contents of Normal Gastric Juice •Volume: 1 -1.5 liters • Nature: acidic pH 0.7 to 4 Constituents: Water (99.5%); solids (0.5%) Inorganic constituents: anions ( Cl- , PO4 3-, SO4 2- & HCO3 - and cations (H+, Na+, K+, Ca++, Mg ++) Organic constituents: pepsinogen, IF, mucin, renin, gastric lipase, gelatinase, carbonic anhydrase and lysozyme.
- 12. 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
- 13. Mechanism of HCl Secretion • Water dissociated into H+ & OH- • Pumping of H+ out of cell by H+K+ATPase; permits OH- to accumulate & form HCO3 - from CO2 • Water passes into canaliculus by osmosis making gastric juice isotonic to plasma
- 15. Pyloric gland Oxyntic gland
- 16. Regulation of HCl Secretion
- 18. Pyloric gland Oxyntic gland Potentiation
- 19. Agents stimulating the parietal cells • Ach • Gastrin • Histamine Agents inhibiting the parietal cells • Acid • Somatostatin
- 20. Meal Related Phases of Gastric Secretion Cephalic phase : 30% Gastric phase: 60% Intestinal phase: 10%
- 22. sight, aroma, taste, thought Cephalic phase
- 23. Sham feeding
- 24. Gastric phase
- 25. Intestinal phase
- 27. Enteric hormones that inhibit gastric H+ secretion
- 28. 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
- 29. • Agonist acting through Ca++ M3 muscarinic receptors for Ach Gastrin/CCk family peptides’ receptors Stimulated by:
- 30. Regulation of Pepsinogen Secretion
- 31. Mucus Secreted by : • Surface mucous cells • Mucous neck cells • Glandular mucous cells • forms a mucus gel layer with PLs, electrolytes , water
- 32. Mucus Secretion & its Regulation •Vagal stimulation and irritation stimulate gastric mucous cells to secrete mucin •Gastric surface cells secrete HCO3 - , stimulated by Ach, Acids & PGs. •Entry of acid into the duodenum induces Secretin from S cells triggering HCO3 - secretion by pancreas/duodenum & neutralizes Gastric acid
- 33. Mucus protects the gastric surface epithelium by trapping an HCO3 - rich fluid near the apical border of these cells
- 34. Gastric mucosal barrier Mucus Bicarbonates Epithelium- tight junctions+ surface membranes Prostaglandins Trefoil peptides
- 35. What we learned today…. •Stomach: Parts, Function and Gastric Glands •Gastric Secretions •Regulation •Phases Of Secretion
- 37. Structure of Gastric Glands and secretions
- 38. Mechanisms sight, aroma, taste, thought -----> hypothalamus gustatory centers -----> vagal nuclei of medulla -----> vagus nerve (parasympathetic) -----> increased gastric secretion
Notas do Editor
- The stomach is a J-shaped, baglike organ that expands to store food (Figure 1). Typical of that of the entire digestive tract, the wall of the stomach contains four layers. However, the inner layer, the mucosa, is modified for the specialized functions of the stomach. In particular, the innermost layer of the mucosa (facing the lumen) contains a layer of simple columnar epithelium consisting of goblet cells. Gastric pits on the surface penetrate deep into the layer, forming ducts whose walls are lined with various gastric glands.
- Not easily but become very prominent with plentiful mitotic figures after damage to the mucosa has occurred, e.g. after an episode of gastritis. ie. important histopathology feature
- Max concn can reach upto 150 meq/L.pepsinogen is secreted from peptic cells and acts best at 2-4 PH. Mucin are of two types insoluble mucin and soluble mucin. Gastric secretion is a colorless, watery, acidic, digestive fluid produced in the stomach . Physical properties; It is a watery fluid, that has a pale yellow colour , pH is 1-3 , the volume secreted per day is 2-3 L . The stomach is famous for its secretion of acid, but acid is only one of four major secretory products of the gastric epithelium, all of which are important either to the digestive process or to control of gastric function. Chemical composition; It is 97-99% water , it contains inorganic salts ,and organic components that include ,mucin, digestive enzymes , hormones ….
- The resting parietal cell has intracellular canaliculi opening in the apicla membrane. And many hace h+ k+ atpase in inactive form
- Postprandial Alkaline Tide
- The resting parietal cell has intracellular canaliculi opening in the apicla membrane. And many hace h+ k+ atpase in inactive form
- Agents inhibiting the parietal cells Acid Somatostatin Food
- Agonist acting through cAMP Chief cells have receptors for secretin/VIP β2 adrenergic receptors EP2 receptors for PGE2
- Lubricating and Protective Properties of Mucus, and Importance of Mucus in the Gastrointestinal Tract Mucus is a thick secretion composed mainly of water, electrolytes, and a mixture of several glycoproteins, which themselves are composed of large polysaccharides bound with much smaller quantities of protein. Mucus is slightly different in different parts of the gastrointestinal tract, but everywhere it has several important characteristics that make it both an excellent lubricant and a protectant for the wall of the gut. First, mucus has adherent qualities that make it adhere tightly to the food or other particles and to spread as a thin film over the surfaces. Second, it has sufficient body that it coats the wall of the gut and prevents actual contact of most food particles with the mucosa. Third, mucus has a low resistance for slippage, so the particles can slide along the epithelium with great ease. Fourth, mucus causes fecal particles to adhere to one another to form the feces that are expelled during a bowel movement. Fifth, mucus is strongly resistant to digestion by the gastrointestinal enzymes. And sixth, the glycoproteins of mucus have amphoteric properties, which means that they are capable of buffering small amounts of either acids or alkalies; also, mucus often contains moderate quantities of bicarbonate ions, which specifically neutralize acids. In summary, mucus has the ability to allow easy slippage of food along the gastrointestinal tract and to prevent excoriative or chemical damage to the epithelium. A person becomes acutely aware of the lubricating qualities of mucus when the salivary glands fail to secrete saliva, because then it is difficult to swallow solid food even when it is eaten along with large amounts of water.