Bicarbonate buffer system

[6] The bicarbonate ion present in the blood plasma is transported to the lungs, where it is dehydrated back into CO2 and released during exhalation.

[8] As calculated by the Henderson–Hasselbalch equation, in order to maintain a normal pH of 7.4 in the blood (whereby the pKa of carbonic acid is 6.1 at physiological temperature), a 20:1 ratio of bicarbonate to carbonic acid must constantly be maintained; this homeostasis is mainly mediated by pH sensors in the medulla oblongata of the brain and probably in the kidneys, linked via negative feedback loops to effectors in the respiratory and renal systems.

[10] By Le Chatelier's principle, the release of CO2 from the lungs pushes the reaction above to the left, causing carbonic anhydrase to form CO2 until all excess protons are removed.

After solving for H+ and applying Henry's law, the equation becomes:[13] where K' is the dissociation constant of carbonic acid, which is equal to 800 nmol/L (since K' = 10−pKaH2CO3 = 10−(6.1) ≈ 8.00×10−7 mol/L = 800 nmol/L).

After multiplying the constants (800 × 0.03 = 24) and solving for HCO−3, the equation is simplified to: where: The bicarbonate buffer system plays a vital role in other tissues as well.

Carbon dioxide, a by-product of cellular respiration , is dissolved in the blood, where it is taken up by red blood cells and converted to carbonic acid by carbonic anhydrase. Most of the carbonic acid then dissociates to bicarbonate and hydrogen ions.