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Comparative Vertebrate Physiology

Comparative Vertebrate Physiology. Digestion in vertebrates. Food reception. Chewing Grind and breakdown food Stimulate saliva production Mix food with saliva. Saliva. Composition 99.5% water, 0.5% protein and electrolytes Protein : amylase, mucus, lysozyme Functions

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Comparative Vertebrate Physiology

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  1. Comparative Vertebrate Physiology Digestion in vertebrates

  2. Food reception • Chewing • Grind and breakdown food • Stimulate saliva production • Mix food with saliva

  3. Saliva • Composition • 99.5% water, 0.5% protein and electrolytes • Protein: amylase, mucus, lysozyme • Functions • Water: softens food • Amylase: polysaccharide breakdown • Mucus: lubrication • Lysozyme: kills bacteria

  4. Process of swallowing

  5. Esophagus • Upper sphincter • Ensures breathing commences • Lower sphincter • Prevents acid reflux (heartburn) • Modified in birds • Crop used to store and partiallydigest food

  6. Stomach anatomy

  7. Stomach motility Lower esophageal sphincter • Cephalic phase • Receptive relaxation • Gastric phase • Gastric peristalsis Doudenum Peristaltic wave Pyloric sphincter Stomach

  8. Gastric motility • Control • 1. Volume of chyme • Smooth muscle excitability • 2. Degree of fluidity • Regulates rate of evacuation

  9. Gastric secretions • 1. HCl • By parietal cells • A. Cephalic phase • HCl secreted • B. Gastric phase • Breakdown proteins to peptides • More distention = more HCl release • Protein + HCl = gastrin release • Gastrin increase HCl release

  10. Gastric secretions • C. Intestinal phase • Inhibits gastric secretions - 3 mechanisms • Decrease parasympathetic stimulation • Local reflex action • Release of secretin, GIP and cholecystokinin

  11. Gastric secretions • 2. Pepsinogen • Stored in chief cells as zymogen granules

  12. Gastric secretions • 3. Mucus • Goblets cells • Functions • Prevents mechanical injury • Self digestion against pepsin • Neutralizes HCl

  13. Gastric emptying - hormones • Regulated by rate and composition of chyme entry into the duodenum

  14. Stomach specialization • Monogastric versus digastric stomach • Cellulose digestion • Ruminants (giraffes, cows, deer, elk) • Symbiotic microorganisms • 4 chambered stomach • Pregastric fermentation

  15. Postgastric fermentation • Colon or enlarged cecum • Cecant digestion • Horses, elephants, perissodactyls • Disadvantage • Microorganisms not digested and assimilated • Cellulose digestion less efficient

  16. Coprophagy • Reingestion of feces to return microbes to proximal gut • e.g. lagomorphs and some rodents • Pellets • Normal hard, dark • Soft, pale (over 50% bacteria, reingested) • Further fermentation produces lactate

  17. Midgut • Chyme enters slowly through the pyloric sphincter Sphincter

  18. Small intestine anatomy

  19. Small intestine anatomy

  20. Pancreas Endocrine portion (Islets of Langerhan’s) Acinar cells secretedigestive enzymes Ducts cells secreteenzymes, aqueous NaHCO3 Exocrine portion(acinar and duct cells)

  21. Pancreas • Endocrine portion • Islets of Langerhan’s • Exocrine portion • Acinar cells (digestive enzymes) • Duct cells (secrete sodium bicarbonate)

  22. Acinar cell secretion • Proteolytic enzymes (trypsin, chymotrypsin carboxypeptidase) • Peptides • Lipase • Fatty acids and monoglycerides • Amylase • Lactose and maltose

  23. Hormones effecting pancreatic secretion • Secretin • Secreted by duodenal mucosa • In response to high [H+] • Increases bicarbonate secretion • Cholecystokinin • Secreted by duodenal and jejunal mucosa • In response to fat and protein • Increases total amount of enzymes secreted • Increases smooth muscle activity of gall bladder Both hormones inhibit gastric motility

  24. Liver • Bile • Bile salts, bicarbonate lecithin, water • Functions • Bile salt and water: emulsifies lipid • Lecithin: prevents reaggregation • Bicarbonate: neutralizes gastric HCl

  25. Enterohepatic circulation Common hepatic duct

  26. Small intestine secretions • Succus entericus • Aqueous salt and mucus • Enterocytes: proteases, lipases, amylases • Functions • Lubrication • Enzyme breakdown

  27. Control of secretion

  28. Absorption • Proteins and sugars • co-transported with sodium apically or by protein transporters

  29. Lipids • Lipase emulsifies triglyceridesinto micelles • Emulsion • Mechanical disruption by stomach • Lecithin prevents reaggregation • Once in cell • Converted to triglyceride • Chylomicron • Exocytosis into lacteal

  30. Hindgut • Functions • Temporary storage of digesta • Absorption of inorganic ions and water (9%) • Bacterial fermentation in herbivores • VFA’s absorbed and used as an energy source in metabolism

  31. Hindgut fermentation • Types • Colon: horse, elephant, wombat • Cecum: rabbit, koala, opossums

  32. Hindgut • Motility • Rhythmical: every 30 minutes • Mass movement: coincides with ileum contraction

  33. Hindgut anatomy • Tenia coli • Haustra alter their location Haustrum Tenia coli Rectum Anal canal External anal sphincter

  34. Water balance • 10 liters of fluid into the tract(98.5% is reabsorbed) • Input • Intake 1.5L, salivary gland 1.5L, stomach 2.5L, liver 0.5L, pancreas 1.5L, small intestine 1.5L, colon 1L • Reabsorbed • Small intestine 9L, colon 0.85L • Output • Feces 0.15L

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