Gastrointestinal Secretions

  1. Water, mucous, K+ secreted everywhere
  2. Duct cells in stomach, goblet cells in intestine secrete mucous
  3. Saliva contains HCO3- and amylase
  4. Gastric - HCl, pepsinogen, gastric lipase, intrinsic factor, water, mucous
  5. Pancreatic - HCO3-, water, amylase, lipase, proteases, nucleases - and inactive Zymogens (must be converted into active form)
  6. 7 L of fluid a day is secreted by GI tract, either through Duct delivery systems or through Direct secretion in the lumen of the alimentary canal (full GI traxt)
  7. Ducts include: salivary ducts, pancreatic ducts, biliary ducts
  8. GI input = GI output
  9. Brunner's gland in duodenum secretes with high basicity due to large concentration of bicarbonate (pH = 8-9)
  10. Saliva is an exocrine secretion - 1.5 L of secretion a day
  11. PSNS controls salivary secretion
  12. Basic secretory unit of saliva is acinar cells - always hypotonic to plasma
  13. Major glands - parotid (serous), submandibular (serous and mucus), sublingual (mucus)
  14. Sensory reflexes, pressure, nausea stimulate secretion
  15. Fatigue, fear, sleep, depression inhibit secretions
  16. Saliva is composed of 99.5% water, along with
    • electrolytes (bicarbonate, sodium, potassium, chloride)
    • mucins
    • WBCs
    • IgA, lysozyme (Paneth cells), lactoferrin, lactoperoxidase
    • Amylase (hydrolysis of starch), lipase (hydrolysis of fats), kallikrein (serine protease)
  17. Minor salivary glands secrete mainly mucous
  18. Problems with dentures mainly involve minor salivary glands
  19. Parotid is 30% of total output and has most of the enzymes and IgA, submandibular is 60% of output
  20. Saliva lubricates, digests, transports, and defends
  21. Saliva facilitates taste and neutralizes gastric acid
  22. Secretion is mainly dependent on calcium ion signaling
  23. Duct cells absorb NaCl, potassium and HCO3- are secreted
  24. Gastric secretions
    • HCl
    • Intrinsic factor - binds B12
    • Pepsinogen
    • Mucous
    • During meals, more H+ secretion, during rest, more NaCl
    • Gastric juice can kill bacteria and parasites
  25. Parietal cells (oxynytic cells) - release HCl, intrinsic factor to active pepsin and kill bacteria
  26. Mucuous cells (duct cells) release mucuous and bicarbonate
  27. Enterochromaffin cells release histamine to stimulate gastric acid secretion (parietal cells)
  28. Chief (peptic) cells release pepsin and gastric lipase
  29. D cells release somatostatin to inhibit gastric acid secretion
  30. G cells release gastrin to stimulate gastric acid secretion
  31. Acetylcholine, gastrin, histamine stimulate parietal cells
  32. In Zollinger-Ellison syndrome (gastrinoma), gastric acid output is greatly increased
  33. Mucuous and bicarbonate protect the surface of the stomach from autodigestion