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dan_dares t1_iyd4m3c wrote

It's via diffusion, the deoxygenated blood has a higher affinity for the oxygen and the haemoglobin will bind to the oxygen easily.

Diffusion isn't very efficient, hence needing a very high surface area and very thin capillary walls in the alveoli.

The blood travels along enough of this diffusion-optimised path to ensure (in a healthy person) that almost all the blood becomes saturated.

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Fallacy_Spotted t1_iye0phm wrote

Diffusion requires no added energy so it is very efficient. It is not optimized for space though.

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dan_dares t1_iye30sq wrote

Efficient takes into account many factors, having to grow a massive organ for gaseous diffusion isn't very efficient.

Insects that rely on diffusion through spiracles, have an upper limit on size as diffusion is so slow

Diffusion is energetically cheap however, so systems evolved around it

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_AlreadyTaken_ t1_iye3ql4 wrote

Which is why you got huge insects in periods of greater oxygen levels like during the Carboniferous.

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dan_dares t1_iye4so7 wrote

Yep the inherent limitation of spiracles..

But the alternative is 8 foot tall insects, so i'll take that.

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LemmeKermitSuicide OP t1_iydg4nx wrote

Ah, I see. Does the O2 molecule need a certain energy to pass over the wall? Is it possible to pass over the wall and not bind to a hemoglobin?

Edit: membrane to wall

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MECHASCHMECK t1_iye931i wrote

Not really! Like others have said, it’s passive diffusion based on the pressure gradient between the air and venous blood. The partial pressure of O2 in the air we breath is about 159 mmHg, about 100 mmHg in your alveoli (average since it’s constantly diffusing), and about 35 mmHg in your venous blood. Transfer occurs in the direction of high to low, so O2 heads for the blood, and CO2 heads out to the air 50 venous to 0.3 air).

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