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GI tract secretion

GI tract secretion. Secretory function of the GI tract. Digestion Movement of food materials Linear movement Mixing Digestion Mechanical Chemical Absorption. Secretion by the GI tract Aids movement Mucus Provides protection Digestion Enzymes Bile acids

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GI tract secretion

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  1. GI tract secretion

  2. Secretory function of the GI tract • Digestion • Movement of food materials • Linear movement • Mixing • Digestion • Mechanical • Chemical • Absorption

  3. Secretion by the GI tract • Aids movement • Mucus • Provides protection • Digestion • Enzymes • Bile acids • In response to the presence of foods in the tract

  4. Anatomical structures • Single cell mucous gland • Mucous cells/goblet cells • Pits • Submucosal glands • Crypts of Lieberkun • Tubular glands • Oxyntic glands in stomach • Complex gland • Salivary • Liver • Pancreas

  5. GI tract secretion • Epithelial stimulation • Direct contact with food • Enteric nerve stimulation • Tactile • Chemical • Distension • Parasympathetic stimulation • Increased secretion in the upper GI tract • Sympathetic stimulation • Increase in some area • Reduced parasympathetic-induced secretion

  6. Mechanism of secretion • Organic materials • Exocytosis • Water and electrolytes • Increased ion uptake • Inward movement of chlorine • Movement of sodium ion • Osmosis • Release of fluids by opening of channels • Hydrostatic pressure

  7. Mucus • Chemical composition • Different among different regions within the tract • Adhesiveness • Ability to coat the tract • Low resistance against movement • High resistance to digestion • Buffering

  8. Saliva

  9. Composition • Serous • Amylase • Mucous • Mucin • Ions • Bicarbonate • Potassium • Low sodium and chloride ion concentrations

  10. Salivary Glands Type of % of total Gland saliva Secreted Parotid Serous Submandibular Mucous / Serous Sublingual Mucous 10% / Serous Buccal Mucous <1% 90%

  11. Saliva and oral hygiene • Removal of pathogens and food particles • Bactericide activity • Immunity

  12. Nervous regulation of secretion • Parasympathetic nervous system • Tactile and taste stimulation of salivatory nuclei • Higher CNS • Regulation of salivatory nuclei • Reflexes • Lower GI tract

  13. Esophageal secretion • Mucus • Lubrication for swallowing • Simple mucous cells • Protection of the lower esophagus • Compound glands located in the lower portion

  14. Gastric secretion • Types of secretion • Mucous cells • Mucus • Oxyntic glands • Hydrochloric acid • Pepsinogen • Intrinsic factor • Pyloric glands • Mucus • gastrin

  15. Phase of secretion 20 % 70 %

  16. Oxyntic glands • Cells • Mucous neck cells • Parietal cells • HCL • Intrinsic factor • Peptic/chief cells • Pepsinigen

  17. HCL • Formed at the villus-like structures inside of canaliculi

  18. LUMEN BLOOD + H+ HO- H2O CO2 CO2 Carbonic Anhydrase Final Results HCl - 155 mEq/L KCl - 15 mEq/L NaCl - 3 mEq.L pH = 0.8 P HCO3 HCO3 H+ K+ K+ K+ K+ H2O P Na+ P Na+ Na+ Na+ Cl- P Cl- Cl- Cl- H2O osmosis

  19. Pepsinogen • Activated by HCL • Secretion • Acetylcholine • Stomach acid • Inhibition of gastric secretion • Reverse enterogastric reflex • Presence of chemicals within the intestine

  20. Pancreatic secretion • Digestive enzymes • Pancreatic acini • Sodium bicarbonate • Ducts

  21. Secretion • Presence of chyme • Determines the composition of pancreatic secretion • Stimulated by • Acetylcholine • Acinar secretion • Cholecystokinin • Acinar secretion • Secretin • Ductal secretion

  22. Pancreatic enzymes • Carbohydrate digestion • Amylase • Protein digestion • Trypsin • Chymotrypsin • Carboxylpolypeptidase • Lipid digestion • Lipase • Cholesterol esterase • Phospholipase

  23. Phase of secretion 20 % pancreatic secretion 5-10 % Pancreatic secretion Majority of secretion (secretin)

  24. Bile secretion • Secretion • Hepatocytes • Initial secretion • Drained into ducts • Secretion to the SI • Accumulation in the gallbladder • Gallbladder • Increased concentrations of bile salts • Removal of sodium ions • Absorption of chloride ions • Osmosis of water

  25. Emptying • In response to fats in the chyme • Secretion of cholecystokinin • Contraction of gallbladder wall and relaxation of the sphincter of Oddi

  26. Function • Fat digestion and absorption • Emulsification • Detergent function • Formation of micelles • Bile is amphipathic in nature (cholesterol plus salt) • Hydrophobic core/pocket for lipids • Bile salts • Recycled • Enterohepatic circulation

  27. Secretion of the small intestine • Compound mucous cells • Brunner’s gland • Site where pacreatic secretion and bile enter the intestine • Alkaline mucus for protection • Added effects with pacreatic bicarbonate ions and bile • Secretion • Tactile stimulation • Irritation • Vagus stimulation • Secretin

  28. Crypts of Liererkuhn • Goblet cells • Mucus • Enterocytes • Water and electrolytes • Secretion • Rapidly reasborbed by the villi

  29. Secretion of the watery mucus • Active secretion of chloride ions • Active secretion of bicarbonate ions • Passive/drag movement of sodium ions • Results of these: • Osmosis

  30. Digestive enzymes • Peptidases • Enzymes for disaccharide digestion • Sucrase • Maltase • Lactase • Isomaltase • Lipase • Secretion • Regulated by the local stimuli • Enteric nervous reflex

  31. Secretion by the large intestine • No enzyme secretion • Only mucus • Bicarbonate ions • Non-mucous cells • Secretion • Tactile stimulation • Local nervous reflex to the cryts of Leiberkuhn • Protection of the large intestine • Acids from bacterial metabolism • Adhesive for feces formation

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