Re: How does the blood buffer system NaHCO3/NaCO3 work in body?

You're correct that the bicarbonate buffering system seems to be non-ideal for maintaining a pH of 7.4, but remember that the body produces lactic acid as a byproduct of respiration, so the excess capacity to buffer acids does serve a purpose. Because the body is constantly exhaling CO₂, the system never reaches equilibrium, but rather holds bicarbonate and dissolved CO₂ steady by the action of the kidneys and lungs.

You can try a Google search for blood+bicarbonate+buffer+pKa for more information.