AAMC 4R Lung question #211

[TheMightyTexan]

Inflation of the lungs in mammals is accomplished by
A) diffusion of gases or D) negative pressure pumping action

I get how effusion would be a better term than diffusion, as inflation is due to the negative pressure formed from the diaphragm, but wouldn't diffusion still inflate the lungs? The answer said that it wouldn't be fast enough...the main thing that tripped me up was "pumping" action.. how is it pumping? wouldn't that be describing a series or cycle of inflation and deflation and not just inflation? This is why i got the question wrong and yeah its a somewhat no brainier question, but i often will over think the dumb questions or under think the more complicated ones... any advise on how to fix that?

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[Czarcasm]

Inflation of the lungs in mammals is accomplished by
A) diffusion of gases or D) negative pressure pumping action

I get how effusion would be a better term than diffusion, as inflation is due to the negative pressure formed from the diaphragm, but wouldn't diffusion still inflate the lungs? The answer said that it wouldn't be fast enough...the main thing that tripped me up was "pumping" action.. how is it pumping? wouldn't that be describing a series or cycle of inflation and deflation and not just inflation? This is why i got the question wrong and yeah its a somewhat no brainier question, but i often will over think the dumb questions or under think the more complicated ones... any advise on how to fix that?

I understand your line of thinking, but in the technical sense, simple diffusion is a more primitive form of oxygen transport/inspiration (nutrients from high to low gradient). In mammals however (multicellular organisms), we rely heavily on the cardiovascular and respiratory system to pump oxygen to all the tissues in the body. If the lungs collapsed, no diffusion would occur and it certainly wouldn't happen between cells located deep inside the body. By contracting the diaphram, we are able to expand the pleural cavity, creating a negative pressure in the lungs that allows oxygen to rush in (at this point, diffusion is occuring), but to get there, we needed to establish a negative pressure first (the gradient). The best answer is D.