Step I Minimum urine pH is 4.5

[ChessMaster3000]

apparently the urine cannot have a pH any lower than 4.5 ,so acid in excess of this is excreted as titratable acids. can anyone explain the physiology of the pH floor. ie, why can't the kidney excrete more free acid?

 

[Myxedema]

That pH is when the concentration gradient becomes too great for the transporters (H+ ATPase, H+/K+ ATPase) to overcome.

 

[Ionian]

apparently the urine cannot have a pH any lower than 4.5 ,so acid in excess of this is excreted as titratable acids. can anyone explain the physiology of the pH floor. ie, why can't the kidney excrete more free acid?

Your blood pH is 7.4
Proximal tubular cells H+ ATPases can only establish a 10:1 H+ gradient (log 10 = 1) minimum 6.4 pH in proximal tubule
Distal to this; tubular cells H+ ATPases can only establish a H+ gradient of 1000:1 (due to tight junctions) (log 1000 = 3) (7.4-3) minimum pH is therefore 4.4

 

[AlmostAnMD]

Are we talking about excrete or secrete? I mean lots of H+ gets secreted, but iirc doesn't most of it just combine with bicarb to make H2CO3, then get broken down into water and CO2 to get reabsorbed?

 

[ChessMaster3000]

Are we talking about excrete or secrete? I mean lots of H+ gets secreted, but iirc doesn't most of it just combine with bicarb to make H2CO3, then get broken down into water and CO2 to get reabsorbed?

sorry if i mistyped, we are talking about excretion.