To perform their function of CO2/O2 exchange the red blood cells have to make contact with the cell wall. Another reason that they must just squeeze through. Brent On 10/14/2018 12:31 PM, Henry Baker wrote:
After additional reading, it appears that RBC's are far from "passive" hemoglobin carriers.
* RBC's appear to emit NO (a vasodilator) when mechanically squeezed, as if to say "open up, so I can get through!" (RBC's can squeeze through capillaries slightly smaller than their diameter by folding over.)
* RBC's appear to also emit NO when pH is low, as if to say "open up, because I'm bringing you a present of fresh O2, which I can tell you need due to the carbonic acid and lactic acid that I'm sensing !"
The reason why capillaries & arterioles don't simply dilate on their own, is that this would lower the blood pressure and divert flow *without bringing in any corresponding oxygen-carrying hemoglobin*. Thus, RBC's can help direct oxygen-rich hemoglobin towards arterioles and capillaries where the pH is lower -- e.g., where the muscles have been working hard & producing carbonic acid and lactic acid.
At 05:21 PM 10/13/2018, Warren D Smith wrote:
--that seems bullshit since other animals have quite different red blood cells. Also, it is quite obvious to anybody who knows anything that hemoglobin in RBCs is superior to just molecules floating in the blood because the conditions are maintainable more precisely, and also more amenable to recycling and less problems with e.g precipitation and bacteria eating you for lunch, to have to worry about (easily life threatening).
"Also, the biconcave shape allows RBC's to undergo extreme deformations while maintaining a constant surface area for gas exchange."
Canham, P.B. "The minimum energy of bending as a possible explanation of the biconcave shape of the human red blood cell. J. Theoretical Biology, 1970. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)
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