Buffers of body fluids:

Body buffers are the first line of defense against acid load. They do not directly remove the hydrogen ion but help in reducing the free hydrogen ions. The hydrogen ion has to be removed by renal mechanism. The common and important buffers are:

Bicarbonate buffer system:

It is the most important buffer system in the plasma or extracellular fluid. It is also referred as bicarbonate- carbonic acid system (NaHCO3/H₂CO₃).

The base constituent bicarbonate is regulated by the kidney and the acid part, carbonic acid is under respiratory control.

If acid like HCl is present it is neutralized by following mechanism:

1. NaHCO₃—– > Na⁺ + HCO₃^–
2. HCl——-> H⁺ + Cl^–
3. HCO3^– + H⁺ —- > H₂CO₃

If base like NaOH is present, then it is neutralized by following mechanism:

1. H₂CO₃ —– > HCO₃^– + H⁺
2. NaOH —— > Na⁺ + OH^–
3. H⁺ + OH^– —— > H₂O

Phosphate Buffer system:

It is important buffer system present in the intracellular fluid and renal tubular fluid. The main elements of this buffer system are H₂PO₄^– and HPO₄^–.

When strong acid HCL is added to the mixture then hydrogen is accepted by HPO4^—to form H₂PO4^–. Similarly, when strong base like NaOH is added then OH^– is buffered to form HPO₄^—.

Protein buffer system:

Proteins are also important buffers and their concentration is very high in the cells. Intracellular buffering is done by these proteins and it is achieved by the hemoglobin and plasma proteins.