Muster: Proximal Tubule Flashcards
Via what transporter is 90 % of glucose reabsorbed in the proximal tubule?
SGLT 2 (sodium-glucose linked transporter)
Transport Maximum
The limit of saturation of the sodium/glucose transporters - at which no additional glucose will be absorbed and will remain in the urine
Normally, what percentage of filtered glucose is reabsorbed in the proximal tubule?
100 %
What level of glucose saturates the sodium-glucose transporters?
15 mM glucose
If you see normal blood glucose but glucose is present in the urine, where do you know you have a problem?
Proximal tubule!
What three things are pumped UP their electrochemical gradient via secondary active transport with sodium?
Glucose
Amino Acids
Phosphorous
What 4 things drive the Na+/H+ pump on the luminal side of the proximal tubule cells?
Increase in CO2 Increase in Angiotensin II Increase in sympathetic NS Decrease in pH -->example is an acidosis
List 5 general steps that occur in the proximal tubule that begin with sodium extrusion and end with bulk water reabsorption?
- Active extrusion of Na+ from epithelial cell to interstitium via Na+/K+ ATPase
- Passive entrance of Na+ from tubular lumen across apical membrane (mostly via Na+/H+ secondary active transporter) into cell to replace sodium removed in step 1
- Parallel movement of anions that must accompany the sodium to preserve electroneutrality (chloride and bicarbonate)
- Osmotic flow of water and solute from interstitium into peritubular capillary
- Bulk flow of water and solute from interstitium into peritubular capillary
What accumulates as it moves through the proximal tubule and is exchanged for formate from the inside of the endothelial cell?
Chloride
What is the point of the formate in the chloride/formate relationship?
Purely recycling!
What is the fate of formate once it leaves the cell?
It combines with H+ (from the Na+/H+ secondary transporter) to form HF (formic acid) which then enters the cell!
Where and how is the H+ ion made that is an antiporter/secondary transporter for Na+?
Inside the cell via carbonic anhydrase!
Via carbonic anhydrase, what else is made besides the H+ ion?
Bicarbonate
What is the fate of bicarbonate?
Leaves the cell and is put back into the blood stream by way of a Na+/HCO3- symporter (3 HCO3- : 1 Na+ ratio).
What is the process called when bicarbonate is put back into the blood stream?
Reclamation