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29 Cards in this Set
- Front
- Back
In what form can carbohydrates be absorbed by intestinal epithelial cells?
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monosaccharides (glucose, galactose, fructose)
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How is starch digested?
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starch is digested by pancreatic and salivary alpha-amylases to oligosaccharides alpha dextrin/maltose/maltotriose, which are hydrolyzed to glucose by brush border enzymes
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How are disaccharides trehalose, lactose, and sucrose digested?
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trehalose -> glucose (trehalase)
lactose -> glucose and galactose (lactase) sucrose -> glucose and fructose (sucrase) |
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How are glucose and galactose transported across the intestinal epithelium?
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across apical via SGLT1 (Na dependent cotransport), across basolat via GLUT2 (facilitated diffusion)
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How is fructose transported across the intestinal epithelium?
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across apical via GLUT5, basolat via GLUT2 (both facilitated diffusion)
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What happens in the absences of brush border lactase?
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lactose intolerance; causes osmotic diarrhea
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What is the difference between endopeptidases and exopeptidases?
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endopeptidases hydrolyze interior peptide bonds of proteins, exopeptidases hydrolyze one AA at a time from the C-terminal ends
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What are endopeptidases and exopeptidases of the GI tract?
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endo: pepsin, trypsin, chymotrypsin, elastase
exo: carboxypeptidases A and B |
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Where does protein digestion first begin?
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in stomach; chief cells s/c pepsinogen -> pepsin in pH 1-3 (becomes denatured in more basic duod environment
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Is pepsin essential for protein digestion? How do we know this?
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no; ppl whose stomach is removed or who do not s/c gastric H (cannot activate pepsinogen) still have normal protein digest/absorp
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What is the activation cascade of pancreatic proteases?
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trypsinogen activated to trypsin by enterokinase (brush border enz), and trypsin activates all other enzymes
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What are the absorbable forms of peptides?
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AAs, dipeptides, tripeptides
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Pancreatic proteases yield AAs, dipeptides, tripeptides, and oligopeptides. What happens to the oligos?
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oligos get further degraded by brush border proteases into absorbable products
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How are AAs absorbed across intestinal epithelial cells?
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apical Na-dependent AA cotransport, basolat facilitated diffusion
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Do all AAs utilize the same carriers?
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no; 4 different carriers for acidic, basic, neutral, and imino AAs
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How are dipeptides and tripeptides absorbed across the intestinal epithelium?
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apical H-dependent di/tripep cotransport, are hydrolyzed to AAs by cytoplasmic peptidases, then basolat facilitated diffusion
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What is the stomach's role in lipid digestion?
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1. mixing (breaks into droplets)
2. lingual and gastric lipase digest ~10% TGs to MGs and FAs 3. CCK slows gastric emptying (stimulated when lipids arrive in duod) |
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What is the small intestine's role in lipid digestion?
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1. bile acids emulsify lipids, increasing surf area for digestion
2. panc lipases hydrolyze lipids to FAs, MGs, chol, lysolecithin 3. hydrophopic lipid products solubilized in micelles by bile acide |
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What are the pancreatic enzymes that digest lipids in the small intestine?
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pancreatic lipases, cholesterol ester hydrolase, phopholipase A2
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What are the 3 types of dietary lipids?
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triglycerides, cholesterol ester, phospholipids
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What are the breakdown products of TGs, cholesterol esters, and phospholipids?
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TGs -> MG, FA, FA (by panc lipases)
Cholesterol ester -> cholesterol, FA (by chol ester hydrolase) Phopholipid -> lysolecithin, FA (by phospholipase A2) |
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How do lipid products get into intestinal epithelial cells?
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micelles bring them into contact w/absorptive surface of intest cells and MGs, chol, and FAs diffuse across luminal membrane
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How are lipid products transported out of intestinal epithelial cells?
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reesterified to TGs, chol E, PLs, and (w/apoproteins) form chylomicrons, which are exocytosed out of cell from Golgi secretory vesicles, enter lymph, to thoracic duct, to blood
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What happens if there is a failure to synthesis Apo B?
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causes abetalipoproteinemia -> person unable to absorb chylomicorns, and thus dietary lipids -> steatorrhea, or buildup of lipid in intest cells
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How might pancreatic disease (e.g. pancreatitis, cystic fibrosis) cause steatorrhea?
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panc cannot make sufficient enzymes necessary for lipid digestion
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How might hypersecretion of gastrin cause steatorrhea?
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increases gastric H s/c, lowers duod pH, inactivates panc lipase (e.g. Zollinger-Ellison synd, or d/o's w/ insufficient panc HCO3 s/c)
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How might ileal resection cause steatorrhea?
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depletion of bile acid pool b/c bile salts arent r/a'd in ileum and don't recirculate to liver
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How might bacterial overgrowth cause steatorrhea?
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leads to deconjugation of bile acids -- bact converts bile salts (low pK, ionized form, water soluble) to bile acids (high pK, nonionized form, lipid soluble) -- bile acids are readily absorbed too early
*this could also be accomplished by low intest pH* |
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How might a decreased number of intestinal cells cause steatorrhea? Example?
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reduces microvillar surf area, and lipid absorp occurs by diffusion, which depends on surf area; tropical sprue
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