Biochem Anyone?

pamnock · Nov 14, 2008

I have a question about the kidney's role in the bicarb-carb acid buffering system:

CO2 + H2O <> H2CO3 <> HCO3 + H+

I know that in acidosis, the kidneys will excrete more H to bring the ph up, and will retain HCO3 somehow. I'm a little confused about H binding to HCO3 creating an acid. We're already in acidosis, so why H2CO3?? Is the carbonic acid then broken down into CO2 & H2Owithhydrogen beingexcreted along with the water to increase ph??? I'm working onan essay for phsiology, and the professor wants details. In acidosis, the reaction is going to the right. Does the action of the kidneys now pull it to the left???????

I'm getting an A in A&P, but I really struggle with the chemisty and need this explained to me in simpleton terms : (

Pam

tonyshuman · Nov 14, 2008

So, I think this is about acid-base equilibria. H2CO3<-> H+ + HCO3- is a reversible reaction, and the rate of the reaction is called k(sub)a. This is usually reported as the pKa of the acid. carbonic acid (H2CO3) has two ionizable protons, and so it has two pKa's. The first pKa is 6.35, which means that at a pH of 6.35, the reaction listed above will be at equilibrium (equal mols of H2CO3 and H+ and HCO3-). when the pH is lower (more acidic), the equilibrium shifts to the left, and there will be more H2CO3 and less HCO3- and H+. When the pH is higher (more basic), there will be more HCO3- and H+ than H2CO3.

I would think that the kidneys excreting H+ will decrease the pH, causing the reaction to shift to the left.

I don't know if that helped, but maybe it did? I'm not familiar with acidosis itself, but I know that HCO3- acts as a buffer to absorb protons from the solution so that the pH of the solution doesn't change drastically when it's around the pKa of H2CO3.

Bo B Bunny · Nov 14, 2008

:yeahthat:

:dunno:huh:goodluck

pamnock · Nov 14, 2008

"HCO3- acts as a buffer to absorb protons from the solution so that the pH of the solution doesn't change drastically when it's around the pKa of H2CO3"

Every little bit of info helps! I think the above relates to what the professor was talking about last night - that the kidneys can tolerate fluxes in the pH rather well.

I know she wants more than just "kidney's excrete H and retain HCO3 when in a state of acidosis", so I'm attempting to better understand the role that the kidneys play. I understand the role the lungs play, but the process ofrenal controlwas a little more complex. :shock:There's tricky part that I'm still trying to grasp about the HCO3 only appearing to be reabsorbed into the renal tubules, but the renal tubules are incapable of reabsorbing HCO3, only the CO2 - so I guess that the H disassociated from the HCO3 is gotten rid of in the urine?

I also have to understand the role of ammonia in this process.

Pam

missyscove · Nov 14, 2008

We just talked about this in my Animal Science Class a week ago, turns out that was the lecture I forgot to record. :?

If you're willing to message me your email address, I could send you the chapter from our text that covers this. It's written by my instructor and is really helpful.

Edit:

I noticed you have your email listed. I'll go ahead and send it to you and hopefully you'll find it useful.

Edited again:
I emailed you the most recent edition of the chapter, but parts of an older version of the book is also on google books! If you need to cite something, you can get the title an whatnot off there.

http://books.google.com/books?hl=en...tSR&sig=xSjCrtthULjQmSrJOj_OBLPAZhg#PPA207,M1

pamnock · Nov 14, 2008

Thank you! Little by little, I'm piecing the process together. We have an exam on Tuesday and I'm completely overwhelmed with the amount of material we have to know for it.

Pam