Tags: Disease.
Hyponatremia (American English) or hyponatraemia (British English) is an electrolyte disturbance in which the sodium ion concentration in the plasma is lower than normal. Sodium is the dominant extracellular cation (positive ion) and cannot freely cross from the interstitial space into the cell because charged sodium ions attract up to 25 water molecules around them creating a large polar structure that is too large to pass through the cell membrane.
