GI absorption.txt

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arimoses
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38993
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GI absorption.txt
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2010-10-01 19:20:08
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GI
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GI absorption
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  1. What type of transport is paracellular transport?
    Passive, dictated by nature of Tight junctions.
  2. What ion generally drives absorption, secretion?
    • Absorption: Na+ movement from mucosa to serosa
    • Secretion: Cl- in opposite direction.
  3. Where does the majority of water absorption take place?
    Proximal small intestine (7000mL/day).
  4. Three secretions in saliva and function?
    • Mucin: lubricate food
    • alpha amylase: begin breakdown
    • Bicarbonate: neutralizes pH.
  5. Three secretions in stomach and function?
    • HCl: activation of pepsin, lower pH - parietal cells
    • Pepsinogen: protein digestion - chief cells
    • Intrinsic factor: absorption of vit B12 - parietal cells.
  6. What are secretagogues?
    • Agents that stimulate net secretion of fluid and electrolytes into intestinal lumen
    • Secretory diarrhea from bacterial enterotoxins.
  7. How is sodium absorbed, what drives the absorption?
    • Passive mechanisms on apical membrane: ion-specific channel (blocked by amiloride), carriers (symport and antiport)
    • Basolateral membrane: Na+/K+ pump.
  8. What is a stimulus for increased Na+ absorption?
    Aldosterone, increases synthesis and translocation of epithelial Na+ channels.
  9. What is acrodermatitis enterpathica?
    Defective Zinc absorption -> deficiencydefect in zinc transport protein hZIP4.
  10. Describe the overall transepithelial K+ movement in the bowels?
    • Absorptive in small intestine
    • Secretory in colon
    • Both passive and active mechanisms.
  11. What are the two mechanisms of Ca absorption?
    • Paracellular: passive, independent of vit D (comes in between cells)
    • Transcellular: active, stimulated by vit D, only in duodenum.
  12. How does phosphate enter the body?
    Through Na/Pi cotransporter on apical side of enterocyte, extruded across basolateral membrane.
  13. How and where is Fe absorbed?
    • Heme: Heme transporter (HT)
    • Nonheme (free iron): DMT1 (divalent metal transporter)
    • Absorbed mainly in duodenum.
  14. What can result from a riboflavin (B2) deficiency?
    Photophobia, glossitis, cheilosis, angular stomatitis.
  15. What can result from a Pyridoxine (B6) deficiency?
    Sideroblastic anemia.
  16. What can result from a niacin (B3) deficiency?
    Pellagra: dermatitis, dementia, diarrhea, death.
  17. What is wernicke's encephalopathy?
    • Triad: Confusion, nystagmus, ataxia
    • results from B1 (thiamine) deficiency.
  18. What is wernicke-korsakoff syndrome?
    Wernicke's encephalopathy with persisten learning and memory deficits.
  19. Where is folate mostly absorbed?
    Deconjugated and absorbed mainly in jejunum.
  20. What is the mechanism of disease for beriberi and wernicke-korsakoff syndrome?
    Alcohol associated thiamine deficiency -> lack of TPP -> deficiency in all reactions that use TP as cofactor (CV and NS mostly).
  21. What can folate deficiency cause?
    • Megaloblastic anemia
    • Affects synthesis of DNA and RNA.
  22. A functional deficiency of folate can lead from what vit deficiency, how?
    • Vitamin B12
    • B12 deficiency leads to overproduction and trapping of folate in inactive methyl form.
  23. Explain the absorption of B12?
    IF secreted by parietal cells bind B12 -> absorbed via specific receptor-mediated process in terminal ileum -> B12 transported across basolateral membrane and taken up by transcobalamin II -> transported into portal circulation.
  24. What are two sensitive measurements for B12 deficiency?
    Serum methylmalonic acid and homocysteine levels.
  25. How can you distinguish cobalamin and folate deficiencies?
    Isolated folate deficiencies have hematopoietic involvement (depletion of folate pool - megaloblastic anemia) and no neurological signs.
  26. Vomiting results in what (pH-wise), diarrhea?
    • Alkalosis - loss of gastric HCl
    • Acidosis - loss of bicarbonate.
  27. What are three types of enzymes the pancreas releases and their functions?
    • Proteases: protein digestion
    • Lipasase: Fat digestion
    • a-amylase: Carbohydrate digestion.
  28. What are the three phases of gastric secretion?
    • Cephalic: sight, taste, smell of food - vagus secretion of Ach
    • Gastric: Vagovagal reflex (stomach distention) - release of gastrin (protein digestion products)
    • Intestinal: CCK release and vagovagal reflex - protein and lipid breakdown products.
  29. What is the rate-limiting step in carbohydrate absorption?
    Brush border Ez (glycosidases), highest activity in jejunum.
  30. What are two transporters of monosaccharides at the luminal side, active or passive?
    Active transporters: GLUT5, SGLT1.
  31. What is a monosaccharide transporter at the basolateral side, active or passive?
    Passive: GLUT2.
  32. Where is lactic acid and short chain fatty acids (SCFA) absorbed?
    Colon.
  33. What are peptones, what do they do?
    • Small peptides released from action of peptin
    • Gastrin release from antral G cells
    • CCK release from duodenal I cells.
  34. What three substances increase HCl secretion in the stomach?
    • Ach - M3 receptor
    • gastrin - CCK-B receptor
    • Histamine - H2 receptor.
  35. How does omeprazole work?
    Irreversible inhibition of H/K ATPase pump, decreased acid secretion by parietal cells.
  36. What cells secrete bicarbonate, what is it for?
    • Mucosal cells, neutralize pH
    • Stimulated by secretin and Ach.
  37. What are 5 protein digestive enzymes secreted by the pancreas?
    Trypsin, pepsin, chymotrypsin, elastase, carboxypeptidase.
  38. Where is protein digestion completed?
    Brush border by: peptidases, dipeptidase, aminopeptidase.
  39. What is lysinuric protein intolerance?
    Disorder of AA transport across basolateral membrane, impaired transport.
  40. What are two essential fatty acids, how do we absorb them?
    • Omega 6: found in corn (linoleic acid) -> arachinoid acid in meat
    • Omega 3: found in algae (linolenic acid) -> eicosapentaenoic acid (EPA) -> Docosahexaenoic acid (DHA) in fish.
  41. What is Hartnup disease or cystinuria?
    • Impaired transport of AA across apical membrane, but normal transport and levels if presented as oligopeptide
    • 10% or hartnup show actual deficiencies.
  42. What are some functions of Omega 6?
    Vasoconstriction, platelet aggregation, inflammation, major component of brain and nerve tissue.
  43. What are some functions of Omega 3?
    • EPA: Vasodilation, decreased inflammation, decreased platelet aggregation
    • DHA: Brain and retina development.
  44. What do lingual and gastric acids preferentially hydrolyze?
    SCFA and MCFA.
  45. What is the function of a colipase?
    Make the lipid accessible to the lipase on the edge of the micelles.
  46. What happens to absorbed LCFA and VLCFA?
    They are re-esterified to TAG inside the enterocyte.
  47. What is ezetimibe, how does it work?
    • It is a drug used to lower plasma cholesterol
    • Inhibits absorption by inhibitin brush border transporter NPC1L1 protein (Neiman pick-C1-like-1).
  48. What is the mutation in abetalipoproteinemia?
    • mutation in microsomal triglyceride transfer protein (MTP)
    • defective ER assembly of chylomicrons.
  49. What is familial hyperchylomicronemia?
    • Defect in LPL or altered ApoCII
    • pancreatitis, hepatosplenomegaly, xanthoma
    • no increased risk for atherosclerosis.
  50. What are some symptomes of Vitamin A deficiency?
    Night blindness, immune deficiency.

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