CAROL AND MIKE WERNER / SCIENCE PHOTO LIBRARY CAROL AND MIKE WERNER / SCIENCE PHOTO LIBRARY
Hyponatremia is an electrolyte imbalance in which the sodium ion concentration in the plasma is lower than normal. Normal serum sodium levels are between approximately 135 and 145 mEq/L. Hyponatremia is generally defined as a serum level of less than 135 mEq/L. Shown on the left is a normal brain. On the right, serum sodium ion level is less than 130 mEq/L and water is drawn into the cells causing the brain to swell. Labelled illustration.
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