pH). By the same principle, when the pH is too high, the kidneys excrete bicarbonate into urine as urea via the urea cycle (or Krebs-Henseleit ornithine cycle). By removing the bicarbonate, more is generated from carbonic acid , which comes from produced by cellular respiration.

Crucially, a similar buffer operates in the oceans. It is a major factor in climate change and the long-term carbon cycle, due to the large number of marine organisms (especially