Electrolyte

In chemistry, an electrolyte is any substance that produces ions when it dissolves in water, so the solution can carry an electric current. Strong electrolytes, such as sodium chloride, separate almost completely into ions, while weak electrolytes, such as acetic acid, separate only partly. In physiology and medicine, the word usually means the charged minerals in body fluids themselves: sodium, potassium, chloride, bicarbonate, calcium, magnesium and phosphate.

Electrolytes have many jobs. Their gradients across cell membranes make nerve and muscle signals possible, sodium largely decides how water is shared between body compartments, bicarbonate and phosphate buffer acids, and calcium is needed for muscle contraction, blood clotting and bone. Sodium is the main positive ion outside cells and potassium the main one inside. The kidneys, steered by hormones such as aldosterone and antidiuretic hormone, keep blood levels within narrow limits by matching what is lost in urine to what comes in from food and drink.

Vomiting, diarrhea, heavy sweating, kidney disease and some drugs, such as diuretics, can upset this balance. A routine blood test, the electrolyte panel, measures sodium, potassium, chloride and bicarbonate, and an abnormal potassium level in particular can disturb heart rhythm.