3.2.3 The kidneys regulate pH levels

The kidneys’ role in regulating the acid balance in the body is relatively complicated. We will not go into the chemical details here, but only briefly mention the role of the kidneys in regulating pH.

There are three renal mechanisms to regulate pH:

• Reabsorption of bicarbonate (HCO₃), which can bind the acid (H⁺) in body fluids
• Production of more bicarbonate in additional to the HCO₃ reabsorbed, which again binds with acids (H⁺) in body fluids
• Secretion of bicarbonate (HCO₃) when in need of more acid in the body fluids

Bicarbonate is the most important buffer in the body.

In simple terms we say that the more bicarbonate, the more acid can be bound by the following equation

HCO₃^– + H⁺ → H2CO₃

This removes the acid from the body. Similarly, if smaller amounts of bicarbonate are available, only smaller amounts of H⁺ can be bound and therefore H⁺ ions  accumulate and pH drops.