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Wednesday, October 21, 2009

Why is it that they say the brain can only remain conscious without oxygen for 13 seconds?

When people can hold their breaths for much longer?
Is it residual oxygen in the lungs and blood that's being "reused" till exhaustion?Because they say you can stay awake for 13 seconds in vacuum if calm, then you blackout and start having brain damage and death.And that decapitated heads can think and feel pain for 13 (probably 6) seconds?Is that because all the air leaves your lungs in a vacuum so it's not available for rebreathing? And likewise, the decapitated heads are quickly removed from their lungs and blood?
Answer:
Holding your breathe and not having oxygen in the blood are two different matters. Your red blood cells carry oxygen to all parts of your body including your brain. The red blood cells replenish their oxygen and discharges carbon dioxide in the lungs. And from there they travel with their load of oxygen to other parts of your body including your brain. That explains why your brain can still have oxygen even when you hold your breathe for as long as you possibly can, and the brain is still alive after being decpitated because there's still blood with oxygen circulating within the brain, although not for long.To a certain extent, yes, there is always residual oxygen in the air sacs within the lungs, but there needs to be a minimum percentage of oxygen in the air sacs for effective transfer of oxygen to the red blood cells because the mechanism of transfer of oxygen from air sacs to the capillaries in the lungs is via diffusion. Diffusion is a movement of molecules from a higher concentration to a lower concentration through a permeable membrane. So if you are in a vacuum (and assuming that the pressure difference within your lungs and the outside vacuum haven't caused your lungs to collapse), obviously you can't breathe and the oxygen level in your lung's air sacs gets lesser and lesser to the point whereby it is lesser than the oxygen level in your red blood cells, then diffusion can't take place anymore.
I DON'T BELIEVE THAT IS TRUE!!
I think I know the answer, correct me if I'm wrong though, not 100% sure. The red cells in your bloodstream (erythrocytes) are the carriers of oxygen. There's a complex system in your lungs that "Recharges" them of oxygen when they pass through the Alveoli (Little balloons inside your lungs, they serve as the main Blood/Gas exchange, they also take the C02 out of your system). That means that most of the Red Cells in your Blood Stream are charged and take air to your cells, in this case the brain. The adult human body has around 5 liters of blood, that are constantly being pumped through the whole circulatory system. When you hold your breath, you basically stop the Gas/Blood interchange, but that doesn't deplete your Red Cells supply of oxygen. Depending on your health (Athletes usually have more erythrocytes and lung capacity, although the later is not that important, it only lets you "charge" more red cells before holding your breath) you can hold your breath for up to 2 minutes, since oxygen is still technically getting to your brain. Alas, when your Red Cells supply of oxygen begins to deplete, less and less oxygen gets to your brain, first making your vision blurry and dizzy, and finally you faint.

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