The figure at illustrates cross-current exchange of O2 between incoming air with

Question

The figure at illustrates cross-current exchange of O2 between incoming air with a Partial pressureO2 of 140 mm Hg and incoming blood with a Partial pressureO2 of 40 mm HgWhat is the value of B, the Partial pressureO2 in the air leaving the lung? This is not a numerical value it is a more of is the pressure more or less than A? Greater than Greater than 140 less than 140, between 100 and 70 or Etc. ... Thanks in advance

Ps. IF you do not know the answer please do not reply that you do not know the answer because that uses one of my questions. thanks

Explanation / Answer

Less than that at A The exchange of gases (O2 & CO2) between the alveoli & the blood occurs by simple diffusion: O2 diffusing from the alveoli into the blood & CO2 from the blood into the alveoli. Diffusion requires a concentration gradient. So, the concentration (or pressure) of O2 in the alveoli must be kept at a higher level than in the blood & the concentration (or pressure) of CO2 in the alveoli must be kept at a lower lever than in the blood.

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