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63 Cards in this Set
- Front
- Back
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what organ is the major site of digestion and absorption?
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small intestine
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T/F
intestinal epithelial cell turnover is slow. |
FALSE
it is rapid (3-6 days) because of stem cells located in villus crypts that produce new enterocytes and mucus secreting goblet cells |
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which organ mainly performs luminal (cavital) digestion?
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pancreas
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what types of enzymes are secreted during luminal digestion? where are they secreted?
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digestive enzymes; GI lumen
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where are the enzymes bound for membrane digestion?
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bound to apical microvilli that comprise the "brush border" of small intestine enterocytes
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where are the enzymes located that perform cytoplasmic digestion?
what type of digestion is cytoplasmic digestion mainly relevant to? |
within cytoplasm of small intestine enterocytes; protein digestion
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In the GI system, where is the nutrient absorptive capacity greatest? the worst?
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duodenum; colon
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how are sugars and amino acids transported into systemic circulation?
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they enter capillaries which lead to the portal system and deposits in the systemic system.
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how are fats transported into the systemic circulation? why?
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they enter the central lacteal and then are deposited in the lymphatics which leads to the systemic system; because fats are too large for GI capillaries.
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what are the four mechanisms that are important in transport of substances across the intestinal cell membrane?
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active transport, passive diffusion, facilitated diffusion and endocytosis.
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what is the single most important process that makes absorption of nutrients possible in small intestine?
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establishment of Na+ electrochemical gradient across the apical epithelial membrane.
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what establishes the Na+ electrochemical gradient?
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Na+- K+ ATPase on the basolateral membrane
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what Na+- coupled transporter mediates the uptake of glucose or galactose from lumen of the small intestine into the enterocyte?
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SGLT 1
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which transporter mediates the efflux of monosaccharides across the basolateral membrane into the interstitial space?
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GLUT 2
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via what transporter does fructose enter the lumen of the small intestine enterocyte?
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GLUT 5
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what site has the highest absorption of carbohydrates, proteins and lipids?
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duodenum
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what site is the last site of absorption of carbohydrates proteins and lipids?
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the proximal ileum
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what site has the highest absorption for calcium, iron, and folate?
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duodenum
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what is the last site of calcium absorption?
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the ileum
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what two things does the stomach absorb well?
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ethanol and aspirin
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what site has the highest absorption for bile acids?
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the proximal ileum
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what is the first site of absorption of bile acids? last?
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first: duodenum
last: ascending colon |
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what site has the highest absorption for cobalamin (Vit B12)? why?
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proximal ileum; its the only site of absorption.
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what kinds of drugs are absorbed well by the rectum?
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steroids and salicylates
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what 2 enzymes are found in salivary glands? what are their respective substrates?
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salivary amylase- (carb)
lingual lipase- (lipid) |
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what two enzymes are associated with the stomach? what are the respective substrates for these enzymes?
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pepsin and gastric lipase - protein
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what 8 enzymes are associated with the exocrine pancreas? what are the respective substrates for these enzymes?
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pancreatic amylase --[carbs]
trypsins, chymotrypsin, carboxypeptidases, elastases--- [protein] lipase-colipase, phospholipase A2, cholesterol esterase --- [lipid] |
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what 9 enzymes are associated with the intestinal mucosa? what are the respective substrates for these enzymes?
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disaccharidases:
sucrase, maltase, lactase, trehalase, alpha-dextrinase nondisaccharidases: enterokinase and peptidase both the of these categories have the carbohydrate substrate. aminooligopeptidase and dipeptidases ---- [protein] |
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where does the final digestion of starch occur?
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at brush border
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for lactose and sucrose, where does digestion only occur at?
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brush border
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which starch bond is resistant to alpha amylase attacks? what do they use to hydrolyze these bonds?
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alpha limit dextrins ---> alpha 1, 6 bonds; membrane bound enzymes
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what is the optimal pH for alpha-amylase?
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neutral
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what bond does alpha- amylase attack?
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interior alpha-1,4,-bonds of amylose
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what are the four products of amylase that leave the stomach and are digested at the brush border?
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alpha-limit dextrins, maltose + 3-9 glucose polymers, lactose and sucrose
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what is the rate limiting step in carbohydrate assimilation?
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absorption
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what type of transporter is GLUT-5?
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facilitated diffusion for fructose
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what does osmotic retention of water in lumen lead to? (because carbs aren't being absorbed effeciently)
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diarrhea, bloating and abdominal pain
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what are the three avenues in which the typical American gets protein?
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diet (mostly), GI secretions and exfoliated intestinal cells
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what are the three cytoplasmic peptidases?
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prolidase, dipeptidase, tripeptidase
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when is pepsinogen secreted and by what cells?
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it is secreted in response to a meal and low gastric pH. Chief cells secrete pepsinogen
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what percentage of total protein digestion does luminal digestion account for?
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10-20%
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when is the activity of pepsin terminated?
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when gastric contents mix with alkaline pancreatic secretions
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what are the two classes of pancreatic proteases? how do they differ?
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endopeptidases (hydrolysis of interior peptide bonds) and exopeptidases (hydrolysis of external peptide bonds)
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what cleaves a hexapeptide from trypsinogen? what does it produce?
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enteropeptidases; trypsin
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what are the three endopeptidases? what are their products?
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trypsinogen, chymotrypsinogen and proelastase. Products are oligopeptides (2-6 amino acids).
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what are the two exopeptidases? what are their products?
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carboxypeptidase A and B - products are single amino acids
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what converts the endo and exopeptidases into their active form?
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trypsin
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what digests the remaining larger peptides into free amino acids and Di/tri peptides (after trypsin)?
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brush border peptidases
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what type of transports do amino acids use to enter the cell?
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proton-dependent amino acid
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T/F
mixtures of free AA and di/trippetides are absorbed into the enterocyte faster than either form alone. |
TRUE!!!!!
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glycerol esterified to 2 FAs and choline is called what?
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phosphatidyl choline
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glycerol esterified to 2 FAs and inositol is called called?
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phosphatidylinositol
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if phospholipase A2 releases FFAs what does it become?
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lysophospholipids (lysolecithins)
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Is the head or tail of a phospholipid polar?
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head
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how does glycerol enter the blood?
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via diffusion
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what inactivates lingual and gastric lipases in the small intestine?
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pancreatic proteases
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what accounts for ~85% of fat hydrolysis?
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pancreatic lipases released into duodenum
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what does pancreatic lipase require? what does it serve as?
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colipase which serves as co-factor for pancreatic lipase by "anchoring" lipase to emulsified fat droplet
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what triggers the release of CCK?
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fatty acids reaching the duodenum
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what are the three components of bile?
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phospholipids, lecithin and unesterified cholesterol
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which chains of fatty acids can passed unchanged into the blood capillaries?
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short and medium chain
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what do enterocytes do with long-chain fatty acids?
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re-synthesize them into TG's in the SER and then form VLDLs that then bud off and are transported via lacteals into the systemic system.
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what is the only water-soluble vitamin that passive diffuses into the small intestine? where in the small intestine?
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pyridoxine (B6); jejunum and ileum
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