· It is the major component of the cations of extracellular fluid and exists in the body in association with the anions like chloride, bicarbonate, phosphate and lactate.
· Sodium ion is mainly associated with chloride and bicarbonate in the regulation of acid-base equilibrium. It maintains osmotic pressure of the body fluids and thus protects the body against excessive fluid loss.
· It plays an important role in the absorption of glucose and nutrients from small intestine.
· Sodium ions are involved in the maintenance of heart beat.
· It maintains the normal neuromuscular functions and it functions in the permeability functioning of the cells.
The normal level of sodium in blood is 310-340 mg/100 ml of blood. Red blood cells contain no sodium ions.
Sodium chloride (Common salt) is the main source of sodium. Bread, cheese and wheat germ are rich sources. Cauliflower, carrot and milk are also good sources of sodium.
For adults the daily requirement is 5 - 10 grams/day.
Sodium is completely absorbed from the gastro intestinal tract. About 95% of the sodium leaving the body is excreted in the urine since sodium is easily absorbed in the intestine.
Adrenal gland secretes hormones called adrenocortical steroids which regulates the metabolism of sodium. In the insufficiency of adrenocortical steroids the serum sodium level is decreased with an increase in sodium excretion. Hyponatremia (Addison’s disease) the condition in which sodium level of blood is below normal and in hypernatremia (Cushing’s syndrome) the sodium level of blood is above the normal range.