[thetada]

Hi,

Any textbook with anything to say about blood pH inevitably focuses on the carbonic acid buffer. The buffer is very interesting and I completely concede its relevance, but there is something I do not see how it can explain - the fact that blood is basic. Wikipedia notes that carbonic acid at a pressure of 10^-8atms has a pH of 7, while at a pressure of 10¹ atms, the pH is 3.42. (https://en.wikipedia.org/wiki/Carbonic_acid#pH_and_composition_of_carbonic_acid_solutions) Extrapolating these data suggest that the higher pressure of blood would predict a lower, rather than a higher pH.

Presumably there are various basic substances in the blood, none of which seem to warrant inclusion in explanations as to how an acid maintains a basic buffer!!

Can anyone shed any light on this please? It would be especially helpful to know the names of any bases that contribute to the maintenance of the blood buffer.

thanks

[Borek]

Carbonic acid is one thing, carbonate buffer is something different, although they are both related.

See for example http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch

[thetada]

Point taken, but I also found this:

"However, the normal blood pH of 7.4 is outside the optimal buffering range; therefore, the addition of protons to the blood due to strenuous exercise may be too great for the buffer alone to effectively control the pH of the blood. When this happens, other organs must help control the amounts of CO2 and HCO3- in the blood"

Figure 4 on the same page has a titration curve showing that blood ph is outside of the "Maximum buffer range."

http://www.chemistry.wustl.edu/~edudev/LabTutorials/Buffer/Buffer.html

They suggest that the pH is maintained thanks to the efforts of other organs, such as the lungs, which jettison CO2.

Anyway, basically what you're telling me is that a carbonic acid buffer can operate above pH 7, right?

[thetada]

Priceless, from an exam question I've established that the ratio of hydrogen carbonate to carbonic acid needs to be 10.5, in order for the pH to be maintained at 7.4. Sums check out.

Thanks for your help Borek