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Partial pressures of gases in blood

When our professor was teaching this subject she kept refferring to how this correlates to atmospheric pressure. Others in the class and myself asked her to be more specific but, it did not help. Can this be explained a little better, just how does pressure of gases in blood correlate with atmospheric pressure? Can you explain Henry's law a bit better--I'm a bit confused? Thank you

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Dear Student,

Simply put: everything is connected!

The exchanges of CO2 and O2 are purely passive. The behaviour of these two gases depend on Dalton's and Henry's Laws.

Dalton's Law states that each gas in a mixture of gases exerts its own pressure as if all the other gases in the mixture were not there. The specific pressure of an individual gas is referred to as the partial pressure. If we add up all of the partial pressures of all of the different gases in the mixture we would arrive at the total pressure of the mixture. Typically, for air this would be "atmospheric pressure" or 760 mm Hg.

In other words, if atmospheric pressure is 760 mm Hg and O2 makes up 21% of the mixture of gases, then the pO2 (partial pressure of O2) would be 0.21 x 760 = 160 mm Hg.

On the other hand, the pCO2 is about 0.3 mm Hg, since its ...