Acid Base Balance

There are many anions and cations within body fluids.

One of the most important of these is the hydrogen ion (H+) even though it is present in comparatively low concentrations.

The concentration of Na+ is one million times greater than H+ [2]. Therefore, to ease interpretation of the H+ concentration [H+], it is expressed as pH:

pH = – log [H+]


As the [H+] increases, pH decreases. Normal pH within the body is 7.35-7.45 (equivalent to a H+ ion concentration of 35-45 nmol/litre) at which enzyme reactions are optimised [3].

A buffer is a weak (incompletely ionised) acid or base which minimises changes in pH by taking up or releasing H+ [3].

Within body fluids, there are multiple buffer systems, for example bicarbonate, phosphate and plasma proteins. Additionally, within blood, haemoglobin acts as a buffer [3].