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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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dan_dares t1_iye30sq wrote

Replying to Fallacy_Spotted (#818,206)

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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MECHASCHMECK t1_iye931i wrote

Replying to LemmeKermitSuicide (#811,587)

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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amitym t1_iyf03xv wrote

It's insanely hyperoptimized in about 11 million different ways. From massively increasing the surface area (iirc it's like over 100 m^(2) or something, for comparison your entire self is only like 2m^(2) on the outside, it's a real Tardis situation), to having ultra-thin diffusion membranes, to a specialized chemistry with an insanely high reaction constant that is then catalyzed even more so that it's beyond absurdly fast.

So yes the oxygen binds to the blood but no they basically aren't given time to bind, it's like a huge desperate crush of oxygen getting sucked into you at the absolutely fastest possible reaction rate that natural chemistry could evolve.

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KeetoNet t1_iyf4lo8 wrote

For a pretty solid and easy to understand primer (101 level), check out Hank Green in Crash Course Anatomy & Physiology - Respiratory System Part 1. Then go back and watch the rest of the series because it's great.

Or even better, start with the series he does on Physics, then Chemistry, then Biology, then A&P and finally Psychology so you have the building blocks in the right order!

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DrRob t1_iyf88wl wrote

Excellent explanations elsewhere in the thread. For me, the 'Oh wow!' factoid is, the gas exchanging surface area in your lungs is the size of a tennis court. Remember that with each heartbeat, just as much blood gets pumped to your lungs (from the right ventricle) as to the rest of your body (from your left ventricle), so there's a whole lotta blood being pumped through a network spreading it as thin as a single red blood cell, over a freakin' tennis court!

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MyFaceSaysItsSugar t1_iyfcvx7 wrote

Replying to DrRob (#834,592)

Yes, a lot of people don’t realize this but we, just like fish, need oxygen to dissolve in fluid before we can use it. But oceans and lakes don’t have very much dissolved oxygen compared to air, so what our lungs have done is create what is basically a pond the size of a tennis court and folded it up to fit in our chest so that there’s this massive surface available for oxygen to dissolve through, and then hemoglobin binds to that oxygen as fast as it’s getting dissolved, which makes space for more oxygen to get dissolved as new air is inhaled.

Whale kidneys look a lot like lungs for this same reason. Whales need to filter a bunch of salt out of the water they ingest as they eat while still holding onto that water, so they need a lot more surface area in their kidneys to produce super concentrated urine that’s kind of an orangey brown color.

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