The role of equilibrium in modulating pH in the respiratory?

Answer 1

The main equilibrium controlling pH in the human body centers around the bicarbonate buffer. Chemically, it is expressed:

H2O + CO2 <=> H2CO3 <=> H+(aq) + HCO3-(aq)

Like most chemical equilibria it can be dragged to the left or to the right by the addition or removal of its constituents.

In this case, it can be dragged right (towards production of H+) acidifying the body if the HCO3- is eliminated. This usually takes place in the kidneys. This process is called Metabolic Acidosis.

It can be dragged to the left (towards reduction of H+) if CO2 is eliminated. This occurs with hyperventilation. This process is called Respiratory Alkalosis.

If the lungs fail, or there is a severe pneumonia, etc and CO2 cannot be eliminated, the equilibrium is pushed to the right (acidosis). This is called Respiratory Acidosis.

Addition of HCO3- or loss of H+ causes a Metabolic Alkalosis shifting the equilibrium left.

The body compensates for each of these processes by means of this equilibrium. The additional H+ of a metabolic acidosis can be reduced by respiratory compensation - hyperventilation causing a compensatory respiratory alkalosis.

Likewise a metabolic alkalosis can be compensated to some degree by the body slowing breathing and allowing CO2 to build up shifting the equilibrium back to the right (compensatory respiratory acidosis). Unfortunately we can only compensate so much because we do need to keep breathing.