Question

What are the three major mechansisms of pH balance.

Answer 1

Regulation of pH balance:

Buffer system:

This is fast acting system and primary regulator of acid base balance. When there is an excessive acid in the body, buffers act to change strong acids to weak acids or to bind acids to neutralize their effects. Buffer consists of a weakly ionized acid or a base and its salt.

Eg., The carbonic acid - bicarbonate buffer system neutralizes hydrochloric acid in the following manner.

HCl + NaH2CO3 gives Nacl + H2CO3(carbonic acid). Then this carbonic acid is broken down to water and carbon dioxide. The carbon dioxide is excreted through the lungs.

Other buffer systems are phosphate buffer system, intra and extra cellular protein buffer system, hemoglobin and cells.

Respiratory system:

The lungs help to maintain noraml pH by excretion of carbon dioxide and water which are byproducts of cellular metabolism. When there is excessive carbon dioxide released in to circulation they combines with water in blood to form carbonic acid. The carbonic acid dissociates into hydrogen ion and bicarbonate. The free hydrogen ion is buffered by hemoglobin molecules and the bicarbonate diffuses into plasma. In pulmonary capillaries this process is reversed and CO2 is formed and excreted by the lungs.

The rate of excretion of CO2 is controlled by the respiratory center in the medulla oblongata in the brain stem. If increased amount of CO2 or hydrogen ion or present the respiratory center stimulates an increased rate and depth of breathing. Respirations are inhibited if the center senses low hydrogen ion or CO2 levels.

Renal system:

The kidneys reabsorb and conserve all the bicarbonate they filter. They can generate additional bicarbonate and eliminate excess hydrogen ions in case of acidosis in blood. Three mechanisms of acid elimination are,

1. Secretion of small amount of free hydrogen ions into the renal tubules.

2. Combination of hydrogen ions with ammonia to form ammo ium.

3. Excretion of weak acids.