Disorders of Water Balance: Hyponatremia
Where Nae + and Ke + are total exchangeable quantities of these cations, and TBW is total body water. Therefore, hyponatremia can develop by an increase in total body water, a decrease in Na+ and K+ or a combination of both. Hyponatremia is a condition of water excess relative to Na+. In a normal individual, hyponatremia does not develop unless water intake is greater than renal excretion. A defect in renal water excretion in the presence of normal water intake is a prerequisite for the development of hyponatremia. This defect in water excretion is due to high circulating levels of antidiuretic hormone (ADH). With retention of water, hyponatremic patients are unable to lower their urine osmolality < 100 mOsm/kg H2O with the exception of those with psychogenic polydipsia and reset osmostat.
KeywordsWater balance disorders Disorders of water balance Hyponatremia Total body water Antidiuretic hormone and water balance Urine osmolality
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