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  1. Announcements • Tomorrow’s quiz on NEJM paper • Bring two questions about NEJM • Exam I provided today

  2. Which of the following enzymes work most effectively at a very low pH? • Salivary amylase • Trypsin • Pepsin • Pancreatic amylase • Pancreatic lipase

  3. In zero gravity environment of space, how does food swallowed by an astronaut reach her stomach? • Swallowing hard • Running around wheel creates -> artificial gravity • Involuntary muscle contractions • IV administration of nutrients

  4. Which of the following organs is incorrectly paired with its function? • Stomach –protein digestion • Oral cavity -starch digestion • Large intestine –bile production • Small intestine –nutrient absorption • Pancreas –enzyme production

  5. 1. MouthMechanical and chemical processing (chewing reduces size of food; saliva digests carbohydrates) Salivary glands Secretes enzymes that digest carbohydrates Liver Secretes molecules required for digestion of fats 2. Esophagus Transports food 3. StomachMechanical and chemical processing (digestion of proteins) 4. Small intestine Chemical processing and absorption (digestion of proteins, fats, carbohydrates; absorption of nutrients and water) Gall bladderStores secretions from liver; empties into small intestine Pancreas Secretes enzymes and other materials into small intestine 5. Large intestineWater absorption and feces formation

  6. Stomach End of esophagus Sphincter seals off stomach from esophagus Sphincter seals off stomach from small intestine Layers of muscle Beginning of small intestine Lumen (interior)

  7. Stomach lining Canal empties to lumen Parietal cells (secrete HCl) Chief cells (secrete pepsinogen)

  8. Secretion of HCI by parietal cells HCl to lumen CO2+ H2O H2CO3 To blood H+ H+ HCO3– HCO3– K+ H+/K+ pump Cl– Cl– Cl– Cl– Chloride channel From blood Canal empties to lumen Parietal cell

  9. Enzymes, Hormones, other? • Enzymes: pepsinogen (inactive)-> pepsin (protease) from chief cells • Other: HCl -> denature ECM bacteria, from parietal cells, activator of pepsin • Other: Mucins/mucus protective from goblet or mucus cells • Other: mechanical churning -> acid chyme • Hormones: Gastrin (+), CCK/secretin (-), enterogastrone (-- pyloric sphinct)

  10. Enzymes, Hormones, other? • Your turn

  11. DIGESTION OF LIPIDS IN SMALL INTESTINE Glycerol Lipase Fatty acids 1. Large fat globules are not digested efficiently by lipase. 2. Bile salts (produced in liver) act as emulsifying agents. 3. Small fat droplets result from emulsification. 4. Lipase digests the small fat droplets into glycerol and free fatty acids.

  12. Fold Villi 115 µm Cross-section of small intestine

  13. Lumen of small intestine Apical side Na+/glucose cotransporter H2O Osmosis Na+ Glucose K+ GLUT-2 transport protein Na+/K+-ATPase K+ ATP Basolateral side ADP Blood H2O Glucose Na+ Osmosis

  14. Capillaries are small and extremely thin walled.

  15. Glycogen Glucose Glycogen Glucose Insulin causes cells in the liver and skeletal muscle to synthesize glycogen; fat storage cells synthesize triglycerides. Pancreas secretes INSULIN If glucose levels too high Glucose levels fall HOMEOTASIS (normal glucose levels in blood) If glucose levels too low Glucose levels rise Pancreas secretes GLUCAGON Glucagon causes cells in liver and skeletal muscle to catabolize glycogen; fat storage cells catabolize fatty acids.