Sodium ions are very important physiologically due to their role in monitoring the function of the nervous system. Sodium ions along with potassium ions regulate the function of the nervous system by maintaining an electric potential across the cellular membrane of neurons. This is done using ions active transport which create and maintain a concentration gradient of these two ions across the cellular membrane of nerve cells and other types of cells as well.
Because of its physiological importance sodium ions concentration in the blood is controlled by a special hormone that the body uses solely for the regulation of this ion. This hormone is called aldosterone. Aldosterone is a steroid hormone that is secreted by the adrenal cortex in response to the hormone renin which in turn is secreted by the kidney cells.
Aldosterone is indirectly secreted in response to hypovolemia which stimulates first the hormone renin which in turn stimulates the secretion of aldosterone. Aldosterone usually and under normal conditions stimulates the conservation of sodium ions into the circulation in exchange for potassium which is secreted in the urine.
Under pathologic conditions of the adrenal cortex in which the hormone aldosterone can be either secreted in excess or in deficient quantities. In both cases there is a marked alteration in the concentration of sodium in the body which can be restored to normal values only by correcting the disorder that involves the secretion of aldosterone.
In the case of hypoaldosteronism there is deficient secretion of the hormone aldosterone mostly due to an autoimmune disorder that destroys the adrenal cortex. In this case there is deficient conservation of sodium ions in the kidney tubules which causes low level of sodium in the extracellular space.
In the case of hyperaldosteronism or excessive secretion of the hormone aldosterone there is marked conservation or reabsorption of sodium in the kidney tubules in exchange for potassium which is secreted in the urine. Excessive secretion of the hormone aldosterone by the adrenal cortex can be caused due to hyperplasia for example of the adrenal cortex.
Excessive administration of sodium ions as in table salt can cause increased concentration of sodium in the blood or hypernatremia. This can cause hypertension and edema due to the concomitant conservation of water which is conserved in the kidney tubules due to the high blood osmolality that is caused by the excessive amount of sodium in the body.
Another important hormone and which affects the concentration of sodium ions in the blood indirectly by diluting its concentration or by concentrating it depending on the concentration of the hormone that regulates the amount of water in the blood. This polypeptide hormone is called antidiuretic hormone.
It is usually secreted in physiological quantities that conserves the amount of water just needed to maintain the physiological concentration of sodium in the blood. Increasing or decreasing the amount of this hormone in the blood will have drastic effect on sodium concentration in the blood. Thus causing either hyponatremia or hypernatremia.
In the case of of deficient secretion of this hormone as occurs in the medical condition diabetes insipidus there is marked elevation of water loss in the urine. Thus concentrating the amount of sodium in the blood which causes hypernatremia. In excessive secretion of this hormone as occurs in certain malignancies in the body such as lung cancer there is marked retention of water in the body due to the effect of this hormone on the kidney tubules. Thus causing a dilutional effect of sodium concentration in the extracellular space.
