Blood is a buffer solution of bicarbonate (HCO₃⁻) and carbon dioxide (CO₂). The Henderson equation which relates the concentration of HCO₃⁻ and CO₂ is given below:
[tex]p^{H}[/tex]=[tex]p^{k_{a} } = p^{H} + log\frac{HCO_{3}^{-} }{CO_{2} }[/tex].
Respiring cell releases CO₂ in blood stream and that CO₂ on reaction with water molecule produces H₂CO₃ which is a weak base and its conjugate base is HCO₃⁻.
CO₂ + 2H₂O⇄ HCO₃⁻ + H₃O⁺
pH of the buffer solution (the blood) depends only on the ratio of the amount of CO₂ to the amount of HCO³⁻. [So, due to respiration produced CO₂ will get dissolved in water and favours the equilibrium towards forward direction. Then immediately HCO₃⁻ reacts with HCO₃⁻ and starts producing CO₂.]This ratio remains relatively constant because the concentrations HCO3- and CO2 are very large compared to the amount of CO₂ produced to the blood from respiring cells. So, [tex]p^{H}[/tex] of blood does not change.
