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.
Read more about this topic: Carbonate
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