The phosphate buffer system(pKa=6.8) has very low concentration in blood. Hence its effect can be practically neglected compared to bicarbonate buffer system(pKa=6.1). The normal bicarbonate level in blood is 22-26 meq/L. The effective pH of the buffered solution can be calculated by the Henderson-Hasselbalch equation as: pH = pKa + log10 ( [HCO3] / 0.03 x pCO2)
The general equation for the action of bicarbonate buffer is:
CO2 + H2O <==C.A.==> H2CO3 <====> H+ + HCO3-
Compensation by this system is more important in case of metabolic acidosis or alkalosis. The pH is sensed by the central and peripheral chemoreceptors and integrated by the medulla which causes appropriate action by controlling the respiratory rate and volume. Acidosis causes hyperventilation causing the release of CO2 and hence the volatile acid H2CO3 normalizing the pH. Alkalosis causes hypoventilation and retention of CO2 and hence doesn’t allow the pH to rise.
Kidneys play an important role in the long term regulation of pH. It does so by regulating acid excretion, bicarbonate reabsorption, H+ secretion and ammonium ion