Submitted by LemmeKermitSuicide t3_z8ssc4 in askscience
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.
Fallacy_Spotted t1_iye0phm wrote
Diffusion requires no added energy so it is very efficient. It is not optimized for space though.
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
_AlreadyTaken_ t1_iye3ql4 wrote
Which is why you got huge insects in periods of greater oxygen levels like during the Carboniferous.
[deleted] t1_iyew255 wrote
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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
FireteamAccount t1_iydhvh6 wrote
Passive diffusion requires no added energy. The difference in oxygen concentration on either side of the wall is all the chemical potential energy required.
threegeeks t1_iydmsoj wrote
Does that mean it's iron-ic...
Sorry, that just popped into my head.
Neat chapter on oxygen transport over on NLM: https://www.ncbi.nlm.nih.gov/books/NBK54103/
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).
sterfri99 t1_iydn835 wrote
To answer your other question, a small amount of oxygen is dissolved in the plasma (~0.3ml O2/100ml blood) and doesn’t bind to hemoglobin.
This here is a great place to learn more https://www.cvphysiology.com/Microcirculation/M002
[deleted] t1_iydu4yb wrote
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[deleted] t1_iyepwz4 wrote
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