Chemical acid base buffer systems

Chemical acid base buffer systems

When there is a change in the H⁺ ion concentration,  the body fluids react immediately to minimize the change. Chemical buffers act by converting either strong acids or bases into weaker acids or bases. The various chemical buffers are-

Bicarbonate

This is the most important buffer system in the body. Bicarbonate combines with H⁺ ions to form carbonic acid in the tubular fluid, which then dissociates to CO₂ and H₂0. The CO₂ formed is removed by the lungs and the HCO₃^– formed in the cells is reabsorbed from the filtrate to the blood.

Phosphate buffer

It plays a major role in buffering renal tubular fluid and ICF. The two main elements of the phosphate buffer are HPO₄^2- (base) and H₂PO₄^– (weak acid). Hydrogen ions from strong acids are captured by converting a weak base to a weak acid and strong base captured by conversion of a weak acid to a weak base.

Protein buffer

It is an intracellular buffer present in high concentrations  in the blood. Hemoglobin molecule forms the second most important blood buffer and is present in the form of proteinate ions (Hb^–). These basic ions, with their weak acids (HHb) form a buffer pair. When an acid is added to the blood,

H⁺ + Hb^– → HHb

This reaction shifts to the right and the ratio of base to acid is decreased. Hemoglobin is a powerful buffer and it binds with protein, CO₂ and H⁺ ions. In the tissues CO₂ passes into the RBC where it combines with water to form carbonic acid which is catalyzed by the enzyme carbonic anhydrase. Carbonic acid then dissociates into HCO₃^– and H⁺ ions. The H⁺ ions binds to hemoglobin to form HHb and the HCO₃^– ions passes back to the plasma in exchange for chloride ions. In the lungs this process is reversed where in H⁺ ions bind to hemoglobin and recombine with bicarbonate to form CO₂ which passes into the alveoli.

Ammonia buffer system

Ammonia is formed by the hydrolysis of glutamine in the presence of enzyme glutaminase in the tubular cells which freely diffuses into luminal fluid and continues with H⁺ ions to form NH₄⁺ ions. This NH₄⁺_­ ions combines with chloride ions and is excreted as ammonium chloride in the urine.