FL 6, C/P Question 55

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FL 6, C/P Question 55

Post by krybczy1 » Mon Aug 13, 2018 7:54 pm

I chose answer choice A because I thought that as you go up in elevation, the percentage of oxygen in the air stays the same, while a drop in atmospheric pressure corresponds with a drop in partial pressure of oxygen. The explanation states that there is less oxygen present, and the increase in hematocrit does not have to do with atmospheric pressure.
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Re: FL 6, C/P Question 55

Post by NS_Tutor_Phil » Mon Aug 13, 2018 10:14 pm

You are absolutely correct. Oxygen accounts for about 21% of the air we breathe, but as we move up, there are less air molecules total. So 21% of the molecules we breath in are Oxygen at elevation, but that is less oxygen overall. So these things are tied together. But imagine the following situation:

We breathe in pure oxygen at a pressure of 0.5 atm. This would mean we are getting more oxygen than normal air at sea level, and this means that we would not increase our hematocrit (even though air pressure is lower!) It's the lack of oxygen that directly causes the change, NOT the air pressure itself.
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