NS FL 6 P/C Q55

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mgarc805
Posts: 33
Joined: Tue Jun 25, 2019 11:23 am

NS FL 6 P/C Q55

Post by mgarc805 » Wed Jul 10, 2019 4:09 pm

What will be the difference in hematocrit between a person living at a higher elevation and a person living at a lower elevation?

A. The person living at a higher elevation will have the higher hematocrit because of the decreased atmospheric pressure.

B. The person living at a higher elevation will have the higher hematocrit because there is less oxygen in the air.

C. The person living at a lower elevation will have the higher hematocrit because of the higher atmospheric pressure.

D. The person living at a lower elevation will have the higher hematocrit because there is more oxygen in the air.

Correct answer: B

There are two major things that confuse me with this question. One I thought that gases like oxygen will distribute uniformly in space (there is no more oxygen in the floor than in the roof of my house). However it is true that people going up the Everest will require oxygen. However, I thought that lack of oxygen was not due to lower O2 concentration but rather to the low pressure making it unable to saturate our lungs. Similar to low O2 pressure will saturate less hemoglobin.
NS_Tutor_Mathias
Posts: 230
Joined: Sat Mar 30, 2019 8:39 pm

Re: NS FL 6 P/C Q55

Post by NS_Tutor_Mathias » Wed Jul 10, 2019 6:41 pm

Here is a quick graphic to explain rarification of gases at higher altitudes: https://imgur.com/a/38aaMUm

In short, forces act on molecules, or when we say forces are acting, we really are saying that molecules are colliding in some sense. So these axioms about the distribution of gases are only helpful guidelines and good approximations. A room fills evenly-ish with a gas because gas molecules bounce off each other. If we look closer, the room is only almost evenly filled, and indeed, very slightly less gas is at the top than the bottom of the room. If we go up on Mount Everest, this will be even more pronounced.

Next, if you recall Dalton's law, you might also be able to intuit that gas pressures and concentrations are the same thing, except we usually use concentration as a measure of dissolved gas and pressure as a measure of well... gas. Recall that the concentration and number of moles of any particular gas is proportional to it's partial pressure. It somewhat follows that the total amount of gas and it's total concentration, are proportional to total pressure. Better yet: Concentrations are just how we ask "How much of this stuff is in a given volume?" while a pressure asks "how much force is acting over a given area?" - the pressure exerted by a gas is due to molecular collisions with a (hypothetical) container, and the more molecules you have, the more collisions you have, and finally that means you will be exerting more force over the same area (simply: pressure).

I can see how this is confusing, but they're essentially all the same thing. Let me know if I can do more to help you out here!

The final part of this question is B&B background, knowing that a physiological feedback loop exists that senses blood O2 concentration, and that the kidneys release erythropoeitin in response to low blood oxygen levels. That hormone in turn stimulates the production of red blood cells.
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