Intestinal Transport 2 Flashcards
qualify the pancreatic peptidases as endo or exo
exopeptidase- carboxypeptidase
endopeptidase- trypsin, chymotrypsin, elastase
what are the products of luminal protein digestion? what are absorbed?
AA and oligopeptides 2-6 AA long
brush border enzymes further digest these
AA and di and tri peptides are absorbed
how do newborns absorb whole ptoreins?
pinocytosis at the microvilli
how are oligopeptides absorbed? what happens to them in the cell?
H+/ oligopeptide cotransporters
they are cleaved to amino acids in the cell
how are amino acids transported out of enterocytes?
Na independent amino acid transporters
how are amino acids absorbed into enterocytesagainst their concentration gradient?
cotransported with sodium along its concentration gradient that is derived from a Na/K pump
what determines Vmax in transport kinetics? how does this apply to AA absorption?
number of transporters on the membrane and the turnover time of each transporter
amino acids share transporters which are saturable
how many AA transporters are there on the brush border? on the basolaeral membrane? how are they classified?
6 on BB, 4 on BLM
classified by the type of amino acids they transport
why is absorption of oligopeptides advantageous?
because it can transport amino acids at a faster rate
which amino acid transporters are defective in hartnup disease? cystinuria?
system B- neutral amino acids
system B0+- basic amino acids
what is ptyalin?
salivary amylase
what is the mechanism of sugar transport into the cell?
facilitated diffusion or sodium coupled cotransport by SGLT1
what does GLUT 5 mediate?
facilitated diffusion of fructose into the enterocyte
what does GLUT 2 mediate in enterocytes?
transport of monosaccharides into the bloodstream
why does lactose intolerance result in diarrhea? gas?
because it is osmotically active
bacteria metabolize the lactose and produce gas by fermentation
how can you test for lactose intolerance?
lactose tolerance test
can test levels of glucose in blood (less if intolerant)
test amount of H2 in breath (made by colonic bacteria)
what causes glucose-galactose malabsorption? what is the result? how are symptoms controlled?
defect in SGLT1 transporters
diarrhea and dehydration- death unless diagnosed
control symptoms with diet restricted to fructose
what three lipases are secreted by the pancreas?
pancreatic lipase, cholesterol esterase and pancreatic phospholipase A2
how are MAG digested in the gut?
if the 2-MAG isomerizes to 1 or 3, pancreatic lipase can cleave it into FA and glycerol (doesn’t always happen)
how are emulsions stabilized by micellse?
they have a negative surface charge that repels other micelles
what do micelles contain?
LCFA, fat soluble vitamins, cholesterol, MAG, phospholipids and bile salts
how do micelles change from emulsion droplets?
multilamellar vesicles bud off and become unilamellar vesicles with more bile salts (one layer of lipid bilayer)
with addition of more bile salts- mixed micelles are formed with a single layer of lipids (not a bilayer)
what happens to short chain FA after they are absorbed? LCFA?
go straight into the blood
LCFA are reesterified
how do LCFA enter the enterocyte? what do they do once they are inside?
FATP4
bind to fatty acid binding protein intracellularly
travel to sER for reesterification
how are lipids transported out of enterocytes?
the lipids pack around a central choleterol ester in the golgi to travel in chylomicrons through the lymph
how is cholesterol absorbed? what inhibits this?
NPC1L1 transporters
ezitimibe is a drug that inhibits these transporters
