Carbonate - Biological Significance

Biological Significance

It works as a buffer in the blood as follows: when pH is too low, the concentration of hydrogen ions is too high, so one exhales CO₂. This will cause the equation to shift left, essentially decreasing the concentration of H+ ions, causing a more basic pH.

When pH is too high, the concentration of hydrogen ions in the blood is too low, so the kidneys excrete bicarbonate (HCO₃−). This causes the equation to shift right, essentially increasing the concentration of hydrogen ions, causing a more acidic pH.

There are 3 important reversible reactions that control the above pH balance.

1. H₂CO₃(aq) H+(aq) + HCO₃-(aq)

2. H₂CO₃(aq) CO₂(aq) + H₂O(l)

3. CO₂(aq) CO₂(g)

Exhaled CO₂(g) depletes CO₂(aq) which in turn consumes H₂CO₃ causing the aforementioned shift left in the first reaction by Le Chatelier's principle. By the same principle when the pH is too high, the kidneys excrete bicarbonate (HCO₃-) into urine as urea via the Urea Cycle (aka the Krebs-Henseleit Ornithine Cycle). By removing the bicarbonate more H+ is generated from carbonic acid (H₂CO₃) which come from CO₂(g) produced by cellular respiration.