proximal tubule (9) Flashcards
about what percentage of filtered water & sodium does the proximal tubule reabsorb?
67%
how much does the Na+ concentration in the PT change?
not at all
what is the transepithelial voltage at the beginning of the PT? at the end?
-3 mV at the beginning, +3 downstream from that
along the length of the PT, what occurs what 3 things increase?
inulin, Cl- and Na+
what 3 things will decrease along the length of the PT?
bicarb, amino acids, glucose
what is the driving force of Na+ across the luminal membrane?
Uptake across the luminal membrane is due to the transepithelial voltage difference (lumen negative)
tell me about the Na+ “backleak” and what causes it
a lumen negative transepithelial voltage difference serves to drive a paracellular “backleak” of Na+ in the EARLY PT and approx 33% of the Na+ transported transcellularly leaks back into the lumen
what are the two ways that Na+ is transported across the PT basal lateral membrane
- primary Na-K ATPase
- secondary active transport via Na+/ HCO3- symport
for chloride, where in the PT does paracellular transport occur?
in the early & late PT
for chloride, where in the PT does transcellular transport occur?
in the late PT
how does Cl- cross the basolateral membrane?
The passive efflux of intracellular Cl- across the basolateral membrane is mediated by a Cl- channel and by a K+/Cl- symporter
what property will permit a large lumen-to peritubule movement of water in response to a small osmotic gradient?
the high water permeability (leakiness) of the PT
how is most of the PT transepithelial water reabsorption occur?
transcellular pathway driven osmotically by transcellular solute reabsorption
where are the two places that H+ comes from to be excreted?
- metabolism of AAs
2. production of organic acids (ex. lactic acid in exercise)
as each H+ gets secreted, what is generated?
a new HCO3- which replaces the HCO3- that is lost in the buffering of the organic & inorganic acids
