Sodium presents in many foods in the form of sodium chloride. About 50% of the total sodium present in the body is found in extracellular fluid. Bone blood plasma and intercellular fluids account for the remaining sodium. Sodium can be easily interchanged between bones and the extracellular fluid. Some of it is found deep down in dense long bones. The concentration of sodium in blood plasma is about 14 times more that present in intracellular fluid.
The absorption of sodium chloride which is an inorganic salt in the diet occurs in the gastro intestinal tract rapidly and practically completed there. Only small amount of sodium occur in the faces. The kidneys regulated the sodium level in the body. When the sodium intake is high excretion is also high and vice- versa. If sodium is restricted in the diet, the excretion of sodium by the healthy kidneys is absent and thus sodium is conserved completely in the body.
Sodium is also lost through perspiration, but this depends upon the concentration in the blood and the total volume of sweat. During the hot season the initial losses may be very high so that sodium depletion syndrome occurs. Salt and fluid intake should increases to make up for the loss of last. Sodium loss in perspiration gets gradually reduced when the body gets acclimatized to the weather conditions. Sodium loss is more in Addison’s disease (deficiency of adrenal hormone) Estrogen hormones favour sodium retention; that accounts for oedema before the onset of menstruation and during pregnancy.
Sodium maintains normal osmotic pressure and water balance as it is the principle electrolyte in extracellular fluid. It is essential for the maintenance of the PH (H ion concentration) of the gastro intestinal secretions. The regulation of the permeability of the cell membrane is due to sodium. The sodium helps to maintain electrolyte difference between intracellular and extracellular fluids.
Common salt or sodium chloride is the chief source of sodium in the diet. It is universally used to flavor the food we eat and is also used for preserving food for long periods. It is found in animal foods, such as Milk, eggs, meat, fish, poultry, and the vegetables, such as spinach, fenugreek, pulses, celery, most of the cereals, fruits and legumes are poor sources of sodium.
8-10 gms of salt (sodium chloride) are sufficient for an average adult. A body adjusts to excess sodium intake. However salt intake is restricted in the case of patients having a high blood pressure, cardiac failure and nephritis.
Osmotic pressure and the pH (H-ion concentration) are seriously affected when there is a disturbance in the concentration of sodium in the extra–cellular fluid of the body tissue. When there is retention of sodium in the tissues, oedema occurs. In the cardiac and renal failure sodium restriction gets reduced. Excessive sodium losses occur during the hot weather causing muscular weakness, cramps, fatigue, vomiting and loss of appetite. In this case a small quantity of salt may be added to the liquid intake. A low consumption of sodium is necessary in case of hypertension, heart disease, and renal disease, cirrhosis, of the liver and in toxaemia of pregnancy.