Kidney

[BestDoctorEver]

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This is probably an easy question, but for some reasons I dont undersrand the explanation provided in my book..

Which of the following occurs in the nephron in response to HIGH pH?

A. Increased in bicarbonate secretion
B. Increased H+ secretion
C. Increased bicarbonate reabsorbtion
D. Increased carbonic acid secretion

Answer: A

Can someone explain in details why this is the answer?

 

[MrBigglesworth]

Increase Bicarb secretion.

Bicarb is a buffer and if there is a high pH that means there is alkalosis and low hydrogen content.

The kidney compensates by dumping bicarb (a base) so that the pH will lower.

 

[BestDoctorEver]

Increase Bicarb secretion.

Bicarb is a buffer and if there is a high pH that means there is alkalosis and low hydrogen content.

The kidney compensates by dumping bicarb (a base) so that the pH will lower.

This seems to be counter intuitive...The body is alraedy basic (high pH) and the kidney is secreting a base to lower the pH...

 

[MrBigglesworth]

Kidney secretes it, meaning it goes in the tubular fluid (urine) and is excreted.

Terms to be familiar with;

Reabsorption - kidney puts it back from tubular fluid into serum (if kidney reabsorbs bicarb, then you would have a more basic (high pH). This is what would happen in a situation of acidosis. The kidney would compensate by absorbing more bicarb

Secretion - kidney puts its from serum into tubular fluid

Excretion - substance is eliminated from the body

 

[Medical Muse]

Not to be too picky, but when the pH is elevated, the kidney gets rid of excess bicarbonate by not reabsorbing it rather than secreting it. The idea of putting more bicarb into the urine is the same, just a different way of doing it.

 

[kasho11]

B, C, and D would all function to RAISE the pH of the blood. If you secrete acid in the urine or absorb bicarbonate back into the blood the pH will go up. A is the only possible answer.

 

[MedPR]

Increase Bicarb secretion.

Bicarb is a buffer and if there is a high pH that means there is alkalosis and low hydrogen content.

The kidney compensates by dumping bicarb (a base) so that the pH will lower.

Bicarb is neither a base nor a buffer. Bicarb is the conjugate base of carbonic acid, but it is still an acid. The reason the body dumps bicarb is not because "bicarb is a base/buffer." It dumps bicarb in order to shift the carbonic acid/bicarb equilibrium in order to decrease pH.

This seems to be counter intuitive...The body is alraedy basic (high pH) and the kidney is secreting a base to lower the pH...

You can think of secretion by the kidney as excretion into urine. Anything the kidney secretes = gets peed out.

Remember this buffer system:

If you remove bicarb, the equilibrium shifts to the left to produce more H+. More H+ = lower pH.

 

[MedPR]

Kidney secretes it, meaning it goes in the tubular fluid (urine) and is excreted.

Terms to be familiar with;

Reabsorption - kidney puts it back from tubular fluid into serum (if kidney reabsorbs bicarb, then you would have a more basic (high pH). This is what would happen in a situation of acidosis. The kidney would compensate by absorbing more bicarb

Secretion - kidney puts its from serum into tubular fluid

Excretion - substance is eliminated from the body

Are you sure about that? What I've learned is that the kidneys reabsorb all of the bicarb (via CO2) under normal conditions and in cases of acidosis will create new bicarb (via carbonic acid and ammonium).

 

[loveoforganic]

Bicarb is neither a base nor a buffer. Bicarb is the conjugate base of carbonic acid, but it is still an acid. The reason the body dumps bicarb is not because "bicarb is a base/buffer." It dumps bicarb in order to shift the carbonic acid/bicarb equilibrium in order to decrease pH.



You can think of secretion by the kidney as excretion into urine. Anything the kidney secretes = gets peed out.

Remember this buffer system:

If you remove bicarb, the equilibrium shifts to the left to produce more H+. More H+ = lower pH.

Bicarb is amphiprotic. In the body, it functions as a base. Don't disagree with the rest. You're just changing the buffer ratio

 

[BestDoctorEver]

Kidney secretes it, meaning it goes in the tubular fluid (urine) and is excreted.

Terms to be familiar with;

Reabsorption - kidney puts it back from tubular fluid into serum (if kidney reabsorbs bicarb, then you would have a more basic (high pH). This is what would happen in a situation of acidosis. The kidney would compensate by absorbing more bicarb

Secretion - kidney puts its from serum into tubular fluid

Excretion - substance is eliminated from the body

Thanks for clarifying these terms because my problems were with these terms most of all.

 

[MedPR]

Thanks for clarifying these terms because my problems were with these terms.

It might help to try and remember that everything the body wants get reabsorbed and everything it doesn't want gets secreted.

I had a hard time with these terms too until I learned it in physio.

 

[BestDoctorEver]

Bicarb is neither a base nor a buffer. Bicarb is the conjugate base of carbonic acid, but it is still an acid. The reason the body dumps bicarb is not because "bicarb is a base/buffer." It dumps bicarb in order to shift the carbonic acid/bicarb equilibrium in order to decrease pH.



You can think of secretion by the kidney as excretion into urine. Anything the kidney secretes = gets peed out.

Remember this buffer system:

If you remove bicarb, the equilibrium shifts to the left to produce more H+. More H+ = lower pH.

Thanks MedPR...Let say the body pH was low...The kidney will reabsorb bicarbonate to bufferize the blood and equilibrium will shift all the way to the right, it does not stop at carbonic acid, right....

 

[MedPR]

Thanks MedPR...Let say the body pH was low...The kidney will reabsorb bicarbonate to bufferize the blood and equilibrium will shift all the way to the right, it does not stop at carbonic acid, right....

Well, I was taught that the kidney is always reabsorbing all of the bicarb that gets filtered. In times of low pH, the kidney creates more bicarb.

Carbonic acid, CO2 + H2O, and bicarb + H+ are in equilibrium, it doesn't "stop" anywhere.