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On Tue, 3 May 1994, Peter R. David wrote: > CO2 is a 'special' gas in my book because its transport in the > body is unusual and not what was stated above. Haemoglobin does not > bind CO2, only O2 and CO. If it binds CO, it does not readily release > it, which is why one dies from CO inhalation. I was taught that hemoglobin (or perhaps more properly, haemoglobin) DID serve a role in the transport of CO2 away from the tissues. Maybe my biochemistry instructor didn't know his stuff, but what of the Bohr effect? I was taught that a drop in ambient pH not only decreased the affinity of Hgb for O2, but increased its affinity for CO2. Is CO2 removed only as dissloved molecules in the blood? > O2 as we all know is primarily transported by hemoglobin in > the red blood cells (at one atmospere! At pressure, I don't know what > the loading levels are, but this is known.). In the tissues, CO2 is > produced by the metabolism of O2. Unlike N2 or Ar, or most other > gases, CO2 is NOT transported in the blood as a neutrally dissolved > gas. CO2 is dissolved in the blood liquid as H2CO3 (Carbonic acid), > which changes the pH and helps release the O2 from the haemaglobin, > along with Di-Phospho-Glycrerol(DPG) in the tissues. During the > transport of the blood from the tissue to the lungs and back, only a > small percentage of the total CO2 present in the blood (at 1 atm!) is > released in the lungs. When the H2CO3 passes through your lungs, the > carbonic acid is converted to CO2 by an enzyme (carbonic anhydrase) at > rapid speeds in your lungs, thus causing the CO2 to outgas in a 'safe' > area. I know that model calculations have been done to model the > effect of higher CO2 levels on the action of the enzyme, but since the > enzyme is limited by the rate of diffusion of CO2 INTO the enzyme, it > should (that's an opinion folks) work at at least the same RATE as on > the surface. However, because the partial pressures in the lungs are > higher at depth, plasma loading of carbonic acid will increase. The > (probable) shift in pH and the presence of more CO2 may well cause the > effects mentioned by Rich Pyle and others. Well, you obviously know more about it than I do (and apparently more than my Biochemistry teacher did...). Thanks very much for your insightful input. I hope you didn't thrash my question in an earlier posting about this topic TOO much :-> Much Aloha, Rich
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