Biology - Arterial CO2/O2 Partial Pressure

[Monkeymaniac]

I've read from TBR passages that partial pressure of O2 in blood represent O2 gas dissolved in blood, not those bound by Hb.

What about arterial partial pressure of CO2? In blood, most of them are exist as HCO3-(l), right? So do we say that the pressure is that of CO2(g) in blood or vapor pressure of HCO3-(l) plus the CO2(g) combined?

Thanks in advance.

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[GreenRabbit]

CO2 partial pressure is only CO2, and besides equilibrium considerations HCO3- is not involved. Just think of partial pressure as analogous to concentration -- e.g. concentrations of CO2 and HCO3- are going to be related by K, but each concentration measures is separate. Same for P(CO2).