Intestinal Transport 2

Question 1

qualify the pancreatic peptidases as endo or exo

Answer 1

exopeptidase- carboxypeptidase

endopeptidase- trypsin, chymotrypsin, elastase

Question 2

what are the products of luminal protein digestion? what are absorbed?

Answer 2

AA and oligopeptides 2-6 AA long
brush border enzymes further digest these
AA and di and tri peptides are absorbed

Question 3

how do newborns absorb whole ptoreins?

Answer 3

pinocytosis at the microvilli

Question 4

how are oligopeptides absorbed? what happens to them in the cell?

Answer 4

H+/ oligopeptide cotransporters

they are cleaved to amino acids in the cell

Question 5

how are amino acids transported out of enterocytes?

Answer 5

Na independent amino acid transporters

Question 6

how are amino acids absorbed into enterocytesagainst their concentration gradient?

Answer 6

cotransported with sodium along its concentration gradient that is derived from a Na/K pump

Question 7

what determines Vmax in transport kinetics? how does this apply to AA absorption?

Answer 7

number of transporters on the membrane and the turnover time of each transporter
amino acids share transporters which are saturable

Question 8

how many AA transporters are there on the brush border? on the basolaeral membrane? how are they classified?

Answer 8

6 on BB, 4 on BLM

classified by the type of amino acids they transport

Question 9

why is absorption of oligopeptides advantageous?

Answer 9

because it can transport amino acids at a faster rate

Question 10

which amino acid transporters are defective in hartnup disease? cystinuria?

Answer 10

system B- neutral amino acids

system B0+- basic amino acids

Question 11

what is ptyalin?

Answer 11

salivary amylase

Question 12

what is the mechanism of sugar transport into the cell?

Answer 12

facilitated diffusion or sodium coupled cotransport by SGLT1

Question 13

what does GLUT 5 mediate?

Answer 13

facilitated diffusion of fructose into the enterocyte

Question 14

what does GLUT 2 mediate in enterocytes?

Answer 14

transport of monosaccharides into the bloodstream

Question 15

why does lactose intolerance result in diarrhea? gas?

Answer 15

because it is osmotically active

bacteria metabolize the lactose and produce gas by fermentation

Question 16

how can you test for lactose intolerance?

Answer 16

lactose tolerance test
can test levels of glucose in blood (less if intolerant)
test amount of H2 in breath (made by colonic bacteria)

Question 17

what causes glucose-galactose malabsorption? what is the result? how are symptoms controlled?

Answer 17

defect in SGLT1 transporters
diarrhea and dehydration- death unless diagnosed
control symptoms with diet restricted to fructose

Question 18

what three lipases are secreted by the pancreas?

Answer 18

pancreatic lipase, cholesterol esterase and pancreatic phospholipase A2

Question 19

how are MAG digested in the gut?

Answer 19

if the 2-MAG isomerizes to 1 or 3, pancreatic lipase can cleave it into FA and glycerol (doesn’t always happen)

Question 20

how are emulsions stabilized by micellse?

Answer 20

they have a negative surface charge that repels other micelles

Question 21

what do micelles contain?

Answer 21

LCFA, fat soluble vitamins, cholesterol, MAG, phospholipids and bile salts

Question 22

how do micelles change from emulsion droplets?

Answer 22

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)

Question 23

what happens to short chain FA after they are absorbed? LCFA?

Answer 23

go straight into the blood

LCFA are reesterified

Question 24

how do LCFA enter the enterocyte? what do they do once they are inside?

Answer 24

FATP4
bind to fatty acid binding protein intracellularly
travel to sER for reesterification

Question 25

how are lipids transported out of enterocytes?

Answer 25

the lipids pack around a central choleterol ester in the golgi to travel in chylomicrons through the lymph

Question 26

how is cholesterol absorbed? what inhibits this?

Answer 26

NPC1L1 transporters

ezitimibe is a drug that inhibits these transporters