Proximal Tubule II - Renal Physiology Flashcards
Where does Cl- increase?
As you go further down the proximal tubule
What transporters are required for Cl- to be reabsorbed?
- 3 Na+/2 K+ ATPase drives everything and creates the concentration gradient for + charge to flow inward
- Na+/H+ transporter at the luminal surface provides H+ for formate to bind and get into the cell.
- Formate/Cl- transporter uses the formate within the cell to drive Cl- back in (reabsorb Cl-)
How does formate get into the cell so that it can be used to drive Cl- in via secondary transport?
It binds to H+ to make formic acid which can diffuse across the membrane into the cell and split into H+ and formate.
From the proximal cell, what flows freely into the peritubular capillary?
K+, Cl- and K+/Cl- can also be transported via a symporter
How else can Cl- be reabsorbed?
Pericellular diffusion, between cells into the peritubular capillary.
What is formate for?
Simply recycling in the proximal tubule
Where are most of the formate anti-porters?
In the late sections of the proximal tubule.
What is the theory behind Cl- accumulating through the proximal tubule?
- Cl- accumulates as it moves through the proximal tubule and by the time it reaches the distal portion, it has achieved a favorable concentration gradient to allow for transcellular movement as well.
- This will generate an electrochemical gradient allowing for some para-cellular movement (through tight junctions) of sodium as well.
What two measurements are NEVER valid in a normal patient?
MDRD or CrCL
What is CrCl?
Estimator for GFR, but it will always overestimate
What is MDRD?
True predictor for GFR
- Standardized to 1.72 m2
- If you don’t adjust for surface area, then your calculation is WRONG
What reabsorption is different than other solutes?
Bicarbonate -> it’s more of a reclamation
Bicarbonate is created and put back into the blood stream.
How is bicarbonate “reabsorbed”?
It’s created and then put back in the blood stream.
When bicarb is secreted at the glomerulus it . . .
. . .is not brought back into the cell/blood, it’s broken into Co2 and H2o
How is bicarb made?
CO2+H2O in the proximal cell is made into H2CO3 with carbonic anhydrase. Then H2CO3 splits into HCO3- and H+. [Rxn would still occur without Carbonic anhydrase]
