Role of CO2 in Bicarbonate
and carbonic acid Buffer System
Carbon dioxide, the acid anhydride of carbonic acid is
continuously produced in the cells. It diffuses into the plasma and reacts with
water to form carbonic acid. The increased carbonic acid is buffered by plasma
proteins. Most CO2 enters the erythrocytes where it either rapidly forms
H2CO3by the action of carbonic anhydrase or combines with
Hb.
The tendency to lower the pH of the erythrocytes due to
increased concentration of H2CO3 is compensated by Hb.
CO2+H2O-------------------------àH2CO3
The bicarbonate anion then diffuses out of erythrocytes and
chloride anion diffuses in. This has been named as chloride shift. Te
bicarbonate in plasma, along with the plasma carbonic acid now acts as efficient
buffer system.
H2CO3+K++ HbO2--------------àK++HCO3-+HHb+O2
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