Resp Physio Question

[Lindyhopper]

I've always been confused about something about gas exchange. If anyone wants to take a crack at it much appreciated.
It's probably better for me to first consider the gas exchange at hard working tissue. The CO2 generated combines with H2O in the RBC --> H2CO3 --> H+ + HCO3- . All the texts all say that this increases H+ conc. thus lowering blood pH.
My confusion stems from the fact that H+ binds Hb (or other proteins); stabilizing the tense conformation in Hb. Meanwhile, HCO3- is exchanged into the plasma for CL-. I don't understand why this doesn't raise blood pH. The H+ remains bound to the Hb while the HCO3- is free to "soak up" plasma H+'s.
Thanks, for any help.

 

[SeventhSon]

the answer lies in the fact that HCO3- is not a great base.

ie this reaction isn't that strong HCO3- + H20 -----> OH- + H2CO3

HCO3- does soak up acid, but the fraction of H+ that does not move into cells to be buffered has a larger effect on the pH. Matter of fact, you can probably view the generation of a bicarb into the serum as the reason (or one of the reasons) that intracellular buffers help keep the blood pH higher than it would be without buffer.

If you think about it another way... it takes mM changes in bicarb to change pH, but it only takes nM changes in H+.