Sodium is an electrolyte, a mineral that is electrically and magnetically charged in the body. It has two basic functions: First, it helps regulate the flow of electrical energy among cells; second, it helps to distribute water in the body. Normal sodium levels are important to health, and high or low levels can be detrimental.
Sodium Regulation
Sodium is ingested in the diet and excreted through sweat, the gastrointestinal tract and the urinary tract. Numerous hormones act together to balance sodium and water concentrations. For example, if the body loses too much water, sodium levels will become more concentrated because there is less water to dissolve the sodium. The brain senses this and releases a hormone called anti-diuretic hormone, or ADH. ADH causes the kidneys to open water channels that absorb more water back into the blood, making the blood more diluted and the urine more concentrated.
Eunatremia
Eunatremia refers to a normal concentration of sodium, which for most people is around 140 mEq/L. Since sodium carries a strong electrical charge, water tends to follow it. Changes in sodium concentrations will cause changes in water balance. Disturbances in sodium can be accompanied by low, normal or high levels of water; these water levels are referred to as hypovolemia, euvolemia or normovolemia, and hypervolemia. At the cellular level, sodium also regulates electrical charge. Cells are negative relative to their surroundings at rest. A stimulus can open sodium channels in the cell, sodium will rush in and make the cell momentarily positive. This causes the cell to perform a function, such as the contraction of skeletal muscle or the beating of the heart.
Hyponatremia
Hyponatremia means a low sodium level, and is usually considered below 135 mEq/L, as above it occurs with low, normal or high fluid levels in the body. Causes of low sodium and low fluid volumes includes excessive prolonged sweating. Normal volume and low sodium can be caused by cancer or several medications. Low sodium in the context of high fluid volume is usually caused by liver, heart or kidney diseases. A person may not experience any symptoms; if they do, symptoms may include fatigue, weakness, coma or seizures. It is often treated by a very slow and gentle administration of sodium and fluid, while fixing the underlying cause.
Hypernatremia
Hypernatremia means a sodium concentration above 145 mEq/L. It is also classified by fluid volume. A low fluid volume with high sodium is caused by diarrhea, inadequate water intake, or loss in the urine. Normal volume and high sodium is caused by a kidney disease in which the kidneys do not respond to ADH or the brain does not release it. High volume and high sodium is frequently caused by hormonal problems. Symptoms of hypernatremia affect the nerves and are similar to hyponatremia. Treatment involves the meticulous administration of free water and correcting the underlying cause.
References
- "Physiology"; Linda S.Costanzo; 4th Ed 2008
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci, et al.; 17th Ed 2008
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