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What type of transport is paracellular transport?
Passive, dictated by nature of Tight junctions.
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What ion generally drives absorption, secretion?
- Absorption: Na+ movement from mucosa to serosa
- Secretion: Cl- in opposite direction.
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Where does the majority of water absorption take place?
Proximal small intestine (7000mL/day).
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Three secretions in saliva and function?
- Mucin: lubricate food
- alpha amylase: begin breakdown
- Bicarbonate: neutralizes pH.
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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.
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What are secretagogues?
- Agents that stimulate net secretion of fluid and electrolytes into intestinal lumen
- Secretory diarrhea from bacterial enterotoxins.
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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.
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What is a stimulus for increased Na+ absorption?
Aldosterone, increases synthesis and translocation of epithelial Na+ channels.
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What is acrodermatitis enterpathica?
Defective Zinc absorption -> deficiencydefect in zinc transport protein hZIP4.
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Describe the overall transepithelial K+ movement in the bowels?
- Absorptive in small intestine
- Secretory in colon
- Both passive and active mechanisms.
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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.
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How does phosphate enter the body?
Through Na/Pi cotransporter on apical side of enterocyte, extruded across basolateral membrane.
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How and where is Fe absorbed?
- Heme: Heme transporter (HT)
- Nonheme (free iron): DMT1 (divalent metal transporter)
- Absorbed mainly in duodenum.
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What can result from a riboflavin (B2) deficiency?
Photophobia, glossitis, cheilosis, angular stomatitis.
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What can result from a Pyridoxine (B6) deficiency?
Sideroblastic anemia.
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What can result from a niacin (B3) deficiency?
Pellagra: dermatitis, dementia, diarrhea, death.
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What is wernicke's encephalopathy?
- Triad: Confusion, nystagmus, ataxia
- results from B1 (thiamine) deficiency.
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What is wernicke-korsakoff syndrome?
Wernicke's encephalopathy with persisten learning and memory deficits.
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Where is folate mostly absorbed?
Deconjugated and absorbed mainly in jejunum.
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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).
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What can folate deficiency cause?
- Megaloblastic anemia
- Affects synthesis of DNA and RNA.
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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.
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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.
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What are two sensitive measurements for B12 deficiency?
Serum methylmalonic acid and homocysteine levels.
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How can you distinguish cobalamin and folate deficiencies?
Isolated folate deficiencies have hematopoietic involvement (depletion of folate pool - megaloblastic anemia) and no neurological signs.
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Vomiting results in what (pH-wise), diarrhea?
- Alkalosis - loss of gastric HCl
- Acidosis - loss of bicarbonate.
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What are three types of enzymes the pancreas releases and their functions?
- Proteases: protein digestion
- Lipasase: Fat digestion
- a-amylase: Carbohydrate digestion.
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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.
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What is the rate-limiting step in carbohydrate absorption?
Brush border Ez (glycosidases), highest activity in jejunum.
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What are two transporters of monosaccharides at the luminal side, active or passive?
Active transporters: GLUT5, SGLT1.
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What is a monosaccharide transporter at the basolateral side, active or passive?
Passive: GLUT2.
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Where is lactic acid and short chain fatty acids (SCFA) absorbed?
Colon.
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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.
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What three substances increase HCl secretion in the stomach?
- Ach - M3 receptor
- gastrin - CCK-B receptor
- Histamine - H2 receptor.
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How does omeprazole work?
Irreversible inhibition of H/K ATPase pump, decreased acid secretion by parietal cells.
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What cells secrete bicarbonate, what is it for?
- Mucosal cells, neutralize pH
- Stimulated by secretin and Ach.
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What are 5 protein digestive enzymes secreted by the pancreas?
Trypsin, pepsin, chymotrypsin, elastase, carboxypeptidase.
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Where is protein digestion completed?
Brush border by: peptidases, dipeptidase, aminopeptidase.
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What is lysinuric protein intolerance?
Disorder of AA transport across basolateral membrane, impaired transport.
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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.
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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.
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What are some functions of Omega 6?
Vasoconstriction, platelet aggregation, inflammation, major component of brain and nerve tissue.
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What are some functions of Omega 3?
- EPA: Vasodilation, decreased inflammation, decreased platelet aggregation
- DHA: Brain and retina development.
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What do lingual and gastric acids preferentially hydrolyze?
SCFA and MCFA.
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What is the function of a colipase?
Make the lipid accessible to the lipase on the edge of the micelles.
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What happens to absorbed LCFA and VLCFA?
They are re-esterified to TAG inside the enterocyte.
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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).
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What is the mutation in abetalipoproteinemia?
- mutation in microsomal triglyceride transfer protein (MTP)
- defective ER assembly of chylomicrons.
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What is familial hyperchylomicronemia?
- Defect in LPL or altered ApoCII
- pancreatitis, hepatosplenomegaly, xanthoma
- no increased risk for atherosclerosis.
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What are some symptomes of Vitamin A deficiency?
Night blindness, immune deficiency.
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