Explain the Maintenance of Electrolyte Balance

In the process of formation of urine, the kidneys also maintain electrolyte balance. Sodium is the most important cation that exists in the extra-cellular fluid of the body. It comes from the diet and common salt. It is lost through the skin as a constituent of sweat and through kidneys as a constituent of urine. The kidneys maintain sodium balance by the help of adrenocortical hormone, aldosterone and also by the renin- angiotensin system. When there is a decreased concentration of sodium, aldosterone secretion increases. It increases the re-absorption of sodium from the glomerular filtrated and the level of sodium is increased in blood. A fall in the concentration of sodium stimulates renin secretion from the kidneys. Renin acts on the serum globulin to form angiotensin. Renin-angiotensin system stimulates aldosterone which helps in increasing sodium reabsorption from the tubules and maintains its concentration in the blood.

Levels of other ions like potassium, chloride, bicarbonate are also maintained along with sodium. When sodium ion reabsorption from the filtrate is increased, potassium ion excretion is increased. Along with potassium ions, hydrogen ions are also secreted into the tubules. When hydrogen ions are secreted, the bicarbonate ions are accumulated in the blood and extra-cellular fluid, as hydrogen comes from carbonic acid (H₂CO₃). Aldosterone causes an enhanced reabsorption of chloride ions.