Blood travels from the heart to the lungs, where it picks up oxygen. Then back to the heart, which (this time) sends it out to the rest of the body. The used blood then comes back from the body to the heart, where the cycle begins anew.
Question:
When the blood reaches the lungs, how deoxygenated is it? Completely, mostly, or just a little bit deoxygenated?
Thinking of two industrial accident scenarios:
A victim’s lungs are seared by hot gases from a fire, eliminating gas transfer to/from the blood.
or
A victim’s lungs are completely filled by carbon dioxide.
If blood is completely deoxygenated upon reaching the lungs, then the victim will be rendered unconscious (due to hypoxia) in the same amount of time in either scenario. OTOH, if blood is only partially deoxygenated, then #2 will result in unconsciousness sooner, since oxygen in this case will diffuse from the blood into the lungs, leaving completely hypoxic blood to be sent out to the body, whereas in #1 blood with serviceable O2 levels will continue to be sent to the body for some time after the initial lung injury.
I respectfully disagree. Under normal circumstances, each molecule of hemoglobin can carry 4 oxygens. I believe that normally only 1 or 2 oxygens dissociate from hemoglobin to be available for metabolism, so it’s only 25-50% deoxygenated.
Sorry mate, you are wrong. The numbers Shmendrik quoted are widely accepted to be the approximate normal values. You are confusing the concept of oxygen saturation with total oxygen content. If you plot pO2 against oxygen saturation, a pO2 of 40mmhg will equate to an oxygen saturation of about 75%.
So yeah, assuming normal conditions, about 60% of the blood’s total oxygen content will be released to peripheral tissue before the blood returns to the lung. Note that that estimation depends on normal lung/cardiovascular/metabolic/hemoglobin function. Anything that alters lung function or changes hemoglobin’s oxygen dissociation curve will alter that rough estimation.
Edit:
I should add that it is possible to increase the blood’s oxygen partial pressure to the point where most of the blood’s oxygen is dissolved, rather than being carried by hemoglobin. A normal response to being put on 100% oxygen is to have a pO2 of like 650.
A separate question is whether the remaining pO2 of 40 is bio-accessible. If there’s no way for the consuming tissues to liberate the 40, it’s effectively a supply of zero.
Lots of physical & chemical systems have limitations like this, where a portion of the payload is captive. I’m cluless about blood oxygen supply, so I can’t offer the answer. But I can say the question needs an answer for us to be able to get to the OP’s questions.
I’d also suggest that oxygen uptake in the lungs is probably not a simple *incoming=empty, outgoing=full *situation either. So the eventual complete answer to the OPs questions will involve a bunch of nuance issues.