27 digestion 2

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27 digestion 2

  1. 1. Digestion 2: Mouth throughStomachChapter 20; pages 570 - 581
  2. 2. Salivary Glands: Fig 20.9
  3. 3. Salivary Glands• Parotid– α amylase (ptyalin)– α 1 - 4 hexose linkages• Submaxillary & Sublingual–mucin (protein for lubrication)
  4. 4. Fig 5.3: Review ofSugar Structure
  5. 5. 1 4 α– linkage
  6. 6. Starch: 1 – 4 & 1 – 6 α linkages
  7. 7. Cellulose: β 1 – 4 linkages
  8. 8. Salivary GlandsAcinus type glands:Primary secretion by secretorycells and then modified by ductcells as saliva passes through onthe way to the oral cavity
  9. 9. Accessory Gland Structure: Fig 20.8Na+K+<--Cl-<-- HCO3-
  10. 10. Saliva• As saliva flows down duct:–[Na+] and [Cl-] decrease–[HCO3-] and [K+] increase– π also decreases - hypotonic• As flow rates increase, this exchange isless complete
  11. 11. Salivary pH• Saliva pH is basic (vs. plasma pH)• WHY?? (i.e., for what purpose?)
  12. 12. Excitatory Signal Molecules• ACh from Parasympathetic NSonto muscarinic receptors• VIP from enteric NS• Increased blood flow in response tokininogen activation
  13. 13. Kininogen Activation• Glands release Kallikrein whenactivated– acts on a kininogen, a plasma globulin• Results cleavage forming a peptide -->bradykinin• Bradykinin ---> local vasodilation (10Xincrease in BF)
  14. 14. Other Components of Saliva• Muramidase --> cleave muramic acid inbacterial cell walls• Lactoferrin --> binds Fe++• Epidermal growth factor --> stimulatesmucosal cell growth• IgA• Lingual lipase (small amounts)• ABO antigens (secreters)
  15. 15. Salivary Secretion• Cephalic Phase–Thought or sensory input• Gastric Phase–Distention–Secretagogues–Vagal - Vagal reflex
  16. 16. Fig 20.29Fig 20.29
  17. 17. Stomach; Figure 20.4
  18. 18. Stomach Mucosal Surface:Folds are calledRugae gastricaeAchalasia: failure to openesophageal sphincter
  19. 19. History Lesson:Alexis St. MartinandWilliam Beaumonthttp://www.james.com/beaumont/dr_life.htmhttp://www.guineapigzero.com/AlexisStMartin.html
  20. 20. Dr. William Beaumont
  21. 21. Beaumont & St. Martin
  22. 22. Stomach; Figure 20.4
  23. 23. Oxyntic Glands• Surface Epithelium - insoluble mucous• Neck Cells - soluble mucous• G cells - gastrin• Parietal (or oxyntic) Cells - HCl & IntrinsicFactor• Chief Cells - pepsinogen
  24. 24. Gastric Acid Secretion: Fig 20.22
  25. 25. PostprandialAlkaline Tide
  26. 26. http://en.wikipedia.org/wiki/File:Control-of-stomach-acid-sec.png
  27. 27. Histamine• From enterochromafin-like cells (ECLcells) in the gastric mucosa• produce, store, & release histamine• activated by ACh, gastrin, &secretagogues
  28. 28. Treatment of Hyperacidity• Atropine•Antihistamine (H2 antagonists)–Cimetidine•Proton pump inhibitors–Nexium
  29. 29. Pepsin• Pepsinogen ---> pepsin in acidicconditions of stomach• It is a family of endopeptidases• pH optima 1.8 - 3.5
  30. 30. Activation of Pepsin; Fig 20.14Activation of Pepsin; Fig 20.14
  31. 31. 1.0 3.0 5.0Gastric pHPepsinActivityµmoles/min/mg enzymeThree Different Pepsins
  32. 32. Vitamin B12• aka, cyanocobalamin• required for nucleicacid synthesis• is very labile in acid
  33. 33. Haptocorrin & Intrinsic Factor• Haptocorrin (transcobalamin) made insalivary glands• binds Vitamin B12 very tightly• protects it from gastric acid digestion
  34. 34. Haptocorrinhttp://en.wikipedia.org/wiki/Haptocorrin
  35. 35. Haptocorrin• Haptocorrin is digested by pancreaticproteolytic enzymes in the duodenum• Vit B12 now binds to Intrinsic Factor (IF)• The B12 – IF complex is taken up byendocytosis in the duodenum
  36. 36. Intrinsic Factor
  37. 37. Secretagogues• caffeine and theophylline• peptides• spices• Alcohol• aspirin
  38. 38. Digestion Review:• ANS and enteric nervous system• Smooth muscle structure - function• Saliva and regulation of flow• Stomach secretions• On to regulation of gastric secretion andmotility (emptying)…….
  39. 39. Table 20.2 Gastrointestinal Hormones
  40. 40. Hormones: GastrinHormone Site of secretion Stimuli ActionsGastrin Stomach Protein digestionproducts instomach,distention, andparasympatheticinputStimulatesgastric secretion& motility,relaxes ileocecalsphincter,stimulates massmovement ofcolon
  41. 41. Hormones: Cholecystokinin(CCK)Hormone Site of secretion Stimuli ActionsCCK Duodenum andjejunumFat or proteindigestionproducts inDuodenumInhibits gastricsecretion &motility,potentiatessecretin action,stimulatespancreaticenzymesecretion,stimulates bilesecretion, andcontracts bileduct and gallbladder
  42. 42. Hormones: SecretinHormone Site of secretion Stimuli ActionsSecretin Duodenum andjejunumAcid induodenumInhibits gastricsecretion &motility,stimulatespancreatic HCO3-secretion,potentiatesactions of CCK,and stimulatesbile secretion byliver
  43. 43. Hormones: GIP(glucose-dependent insulinotropic peptide)Hormone Site of secretion Stimuli ActionsGIP Duodenum andjejunumGlucose, fats oracid induodenum anddistention of theduodenumInhibits gastricsecretion &motility,stimulates insulinsecretion by thepancreas
  44. 44. Contol of G.I. Function: Fig. 21.21
  45. 45. GASTRIN• Peptide hormone• From G cells (stomach)• Increases HCL & pepsinogen secretion• Increases gastric motility and emptyinginto duodenum
  46. 46. Gastric Acid Secretion:Cephalic Phase Fig 20.23a• Thought of food, smell, chewing,swallowing• Vagus nerve to parietal cells (ACh)• Vagus nerve (ACh) onto G cells & thuscauses gastrin release• See TABLE 20.2 !!!!!
  47. 47. Fig 20.23aCephalicPhaseof GastricSecretion
  48. 48. Fig 20.23bGastric Phaseof GastricSecretion
  49. 49. Gastric Acid Secretion:Intestinal Phase• Stimulus - digested peptides, peptidesin duodenum, distention• G cells (gastrin)• distention -->Intestinal endocrine cellsrelease CCK, Secretin, & GIP• see Table 20-2
  50. 50. Inhibition of Gastric Secretion• Important for protection of duodenum• Acid in duodenum ---> secretin &CCK---> inhibits gastric secretion andmotilitySee Table 20.2 for sure !!!
  51. 51. Inhibition of Gastric Secretion• Acid, fats, hyper-osmotic solutions in theduodenum ---> release of enterogastrones---> inhibit gastric motility and secretion• Gastric Inhibitory Peptide or Glucose-dependent Insulinogenic Peptide (GIP) fromduodenum ---> inhibits parietal cell function–Decreases release of acid, motility, & secretion–Increases release of insulin from pancreas
  52. 52. • Ulcers - page 576–Peptic & Duodenal–Role of Helicobacter pylori• Vomit reflex - page 599–Note sympathetic symptoms

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