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 partially digest food

6. Stomach anatomy

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

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

20. Pancreas Endocrine portion (Islets of Langerhan’s) Exocrine portion (acinar and duct cells) Acinar cells secrete digestive enzymes Ducts cells secrete enzymes, aqueous NaHCO 3

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 triglycerides into 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