1. Gastrointestinal Physiology – Part 2 11/04

2. Digestive secretions: saliva Functions of saliva in non-ruminants: –Lubricates food to facilitate swallowing –Contains antibodies and lysozyme –Some amylase in saliva of swine and rats, but much less than in humans Functions of saliva in ruminants: –Maintains fluid consistency of rumen –Slightly alkaline; helps neutralize acids formed by fermentation –May help prevent frothing in rumen

3. Gastric pits in gastric mucosa Gastric pits are openings to ducts into which gastric glands empty their secretions

4. Exocrine gland Any gland that directs its secretions through a duct into a compartment that is contiguous with the exterior of the body

5. Glandular regions of simple stomach Cardiac Fundic Pyloric

6. Glandular regions of equine, porcine and ruminant stomachs Cardiac, fundic and pyloric gland regions are glandular Esophageal regions (“E”) are non-glandular epithelium

7. Cardiac gland region (cardiac mucosa) Cardiac Fundic Pyloric

8. Fundic gland region Mucous neck cells Parietal cells Chief cells Cardiac Fundic Pyloric

9. Fundic gland region Mucous neck cells secrete mucus Parietal cells secrete: –HCl –Intrinsic factor (not in cats); necessary for absorption of Vitamin B12

10. Fundic gland region Chief cells secrete pepsinogen –HCl converts pepsinogen into pepsin –Pepsin is a proteolytic enzyme (breaks down proteins into peptides)

11. Pyloric gland region Mucous secreting cells G cells Cardiac Fundic Pyloric

12. Pyloric gland region G cells are endocrine gland cells – secrete the endocrine hormone, gastrin Endocrine cells secrete hormones into the bloodstream – travel to a distant part of the body where they produce an effect on another cell type

13. Substances that stimulate HCl secretion by parietal cell Gastrin Acetylcholine Histamine –Histamine secreted by ECL cells in gastric mucosa Gastrin may interact with either receptor

14. Rennin Enzyme secreted by abomasal mucosa of young ruminant –Acts to coagulate milk protein, which facilitates its digestion

15. Hormone secretions of small intestine: cholecystokinin Site of secretion Stimuli for secretion Actions Primarily duodenal mucosa Chyme with a: High amino acid concentration High fatty acid concentration Low pH Inhibits gastric emptying ↑ secretion of pancreatic enzymes and HCO 3 - Stimulates gall bladder contractions

16. Hormone secretions of the small intestine: secretin Site of secretionStimuli for secretion Actions Duodenal mucosa Chyme with a: Low pH High fatty acid concentration ↓ HCl production in stomach ↑ pancreatic HCO 3 - secretion ↑ biliary HCO 3 - secretion

17. Exocrine pancreatic secretions Liquid rich in HCO 3 - Pancreatic digestive enzymes Both are secreted into duodenum

18. Pancreatic digestive enzymes Pancreatic proteolytic enzymes (pancreatic proteases) are secreted as proenzymes (zymogens)

19. Activation of pancreatic proteases in small intestine CCK stimulates duodenal mucosal cells to produce enteropeptidase ProelastaseElastase

20. Absorption of amino acids from small intestine

21. Hormone secretions of small intestine: CCK Site of secretion Stimuli for secretion Actions Primarily duodenal mucosa Chyme with a: High amino acid concentration High fatty acid concentration Low pH Inhibits gastric emptying ↑ secretion of pancreatic enzymes and HCO 3 - Stimulates release of enteropeptidase Stimulates gall bladder contractions

22. Carbohydrate digestion Pancreatic amylase breaks down starches into smaller polysaccharides Intestinal mucosal cells release maltase, sucrase and lactase

23. Absorption of monosaccharides from small intestine Most adult animals are unable to produce lactase

24. Action of pancreatic lipase

25. Digestive secretions of liver Bile salts synthesized by hepatocytes from cholesterol

26. Bile salts emulsify dietary fats Emulsification provides greater surface area for action of lipases

27. Bile salts Help absorption of lipids – fatty acids, monoglycerides, cholesterol, fat- soluble vitamins – from small intestine

28. CCK: most important stimulus for gall bladder contraction and release of bile into small intestine

29. Hormone secretions of small intestine: CCK Site of secretion Stimuli for secretion Actions Primarily duodenal mucosa Chyme with a: High amino acid concentration High fatty acid concentration Low pH Inhibits gastric emptying ↑ secretion of pancreatic enzymes and HCO 3 - Stimulates release of enteropeptidase Stimulates gall bladder contractions

30. Hormone secretions of the small intestine: secretin Site of secretionStimuli for secretion Actions Duodenal mucosa Chyme with a: Low pH High fatty acid concentration ↓ HCl production in stomach ↑ pancreatic HCO 3 - secretion ↑ biliary HCO 3 - secretion

33. Carbohydrate digestion

34. Absorption of monosaccharides

35. Action of lipase on triglycerides