GI Transporters Flashcards
How does alcohol get absorbed in the GI system?
simple diffusion - it’s lipid soluble so it will just go right thorugh
WHat are the three types of facilitative diffusion in the gut?
pores (always open)
gated channels (sometimes open)
carrier proteins
WHat is the difference between facilitative diffusion and active transport?
facilitative diffusion just helps molecules move down their concnetration gradients
active transport requires ATP fto move things up their gradients
How do the kinetics differ between passive diffusion and carrier-mediated diffusion?
passive has no max - the higher the concentration of the substance, the more will be absorbed - it’s a linear relationship
WIth the facilitated, there is a maximum number of transporters, so there is a maximum rate of absorption - it reaches a V max
Describe briefly the structure of human GLUTs.
They are a 12-transmembrane protein with intracellular C terminal and loops with a binding site for the sugar
Which GLUT is the most common on RBCs and many other tissues?
GLUT1
Which GLUT is insulin sensitive?
Glut4
What are the ATP-Cassette binding transporters used for?
They’re efflux pumps that will pump bad stuff out
P-glycoprotein is a member
Where in the small intestine are most of the specific transporters for nutritnets and water located?
jejunum
What type of transport is primarily located on the apical side?
active transport requiring ATP
What type of transport is primarily located on thebasolateral side?
carrier-mediated diffusion
Which side are the ABC-type transporters located?
both
The ileum can be called on for absorption if anytning useful makes it though the duodenum. How about the colon?
transverse colon is for reclamation of fluid, electrolytes and bile salts
Why is it a good idea to have ABC-type transporters in the GI system?
It makes sense because the GIt ract is exposed to many potentially toxic substances in the things we eat and drink
having the ABC-type transporters in the gut gives the gut epithelial cells a chance to spit back bad things into the lumen for excretion
How does the parietal cell make acid?
- K activates an H/K ATPase, which will exchange K for an H - the H goes into the lumen
- A chloride channel opens and Cl moves out the cell into the lumen to join with the H and form HCl
Note that the H originatelly came from a dissociation of carbonic acid into bicarb, a reaction that is made favorable in the epithelial cell due to a pumping of bicarb out of the cell into the blood in exchange for Cl (which then goes into the lumen to make the HCl)
What does omeprazole do to the parietal cell to block acid formation?
A sulfur group on the drug interacts with a sulfure group on the H/K ATPase such that they form a complex that inactivates the tranporter.
What are the two general routes for tranpsort of molecules and ions across the epithelium of the gut?
- transcellular
2. paracellular
What about the epithleial cells of the GI system limit paracellular transport?
tight junctions
What two distinct processes establish an osmotic gradient that pulls water into the lumen of the intestine?
- increased luminal osmotic pressure resulting from influx and digestion of foodstuffs
- crypt cells actively secreting electroltyes leading to water secretion (as in CFTR and cholera=diarrhea)
What is probably the most important process that takes place in the small intestine to make such absorption possible?
Establishing an electrochemical gradient of sodium using the NaK ATPase
What transporter takes glucose into the intestinal epithelial cells?
SGLT1
sodium-dependent glucose transporter 1
What transporter takes fructose intot he intestinal epithelial cells?
GLUT5
Five = Fructose
What basolateral transporter will pump both glucose and fructose intot he blood?
GLUT2
2 = both
What form must proteins be in for gut epithelial cells to take them in?
They need to be small - either amino acids, dipeptides or tripeptides
