SODIUM METABOLISM

METABOLISM OF SODIUM

1. Sodium Gandham.Rajeev

2. Sodium is the chief electrolyte which is found in large concentration in extracellular fluid compartment . The total body content of sodium is 3,700 mmol or 1.8 gm/kg of which approximately 75% is exchangeable & 25 % is non-exchangeable , which is incorporated into tissues such as bones. The sodium is found in the body mainly associated with chlorides as NaCl and NaHCO 3 .

3. Sources: Table salt ( NaCl ), salty foods, animal foods, milk, baking soda, eggs, and cereals, carrot, tomato, legumes . RDA: 1 to 5 gm 1gm NaCl per day with history of hypertension.

4. Absorption and excretion Sodium is absorbed by sodium pump situated in basal and lateral plasma membrane of intestinal and renal cells. Na-pump actively transports Na into extracellular fluid. There is normally little loss of these ions through the skin (sweat) and in the faeces .

5. Metabolic functions It maintains the osmatic pressure & water balance. It is constituent of buffer & involved in the maintenance of acid-base balance. It maintains muscle & nerve irritability at the proper level. Sodium is involved in cell membrane permeability. Normal serum sodium: 135-145 mEq /L

6. Disorders of sodium metabolism Hyponatremia : Hyponatremia is defined as abnormally low serum sodium concentration that is lower than 130 mEq /L.

7. Causes of hyponatremia Retention of water: Retention of water dilutes the constituents of extracellular space causing hyponatremia , e.g. heart failure, liver diseases, nephrotic syndrome, renal failure, syndromes of inappropriate ADH secretion.

8. Loss of sodium Occurs only when there is pathological sodium loss. Such losses may be from gastrointestinal tract, e.g. vomiting, diarrhoea , fistula or in urine. Urinary loses may be due to aldosterone deficiency (Addison’s disease)

9. Symptoms of hyponatremia Symptoms are constant thirst, muscle cramps, nausea, vomiting, abdominal cramps, weakness and lethargy. Hypernatremia : Hypernatremia is defined as an abnormal high serum sodium concentration of more than 145 mmol /L. In hypernatremia , the total body sodium content is high with respect to water. Hypernatremia is usually due to excessive water loss compared to increased body sodium.

10. Causes of hypernatremia Water depletion, may arise from a decreased intake or excessive loss with normal sodium content. e.g. Diabetes insipidus . Water and sodium depletion, if more water than sodium is lost, e.g. diabetes mellitus and excessive sweating or diarrhoea in children.

11. Excessive sodium intake or retention, in the ECF due to excessive aldosterone secretion, e.g. Cohn’s syndrome, and in Cushing’s syndrome, where there is excess cortisol production due to hyperactivity of adrenal cortex. Cortisol has mineralocorticoid activity.

12. Symptoms of hypernatremia If hypernatremia is due to water loss, then the symptoms are therefore those of dehydration and if it is due to excess salt gain, leads to hypertension and oedema .

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