Potassium, sodium and chloride are known as electrolytes as they conduct electricity when dissolved in water. Potassium and sodium become positive ions as they lose an electron when dissolved and chloride becomes a negative ion as it gains an electron when dissolved. A positive ion is always accompanied by a negative ion, hence the close relationship between sodium, potassium and chloride. The electrolytes are distributed throughout all body fluids including the blood, lymph, and the fluid inside and outside cells.

What they do in the body

Water balance

The electrolytes are vital for maintaining a normal balance of water between body cells and the surrounding fluids, and for moving fluids in and out of cells. Sodium is the main positive ion outside cells and potassium is the main positive ion inside cells.

The blood and other fluids require a narrow range of sodium concentration to function properly. This balance is accomplished by the hormone, aldosterone. When sodium intake is high, the aldosterone level is low, and the kidney excretes more sodium into the urine. When sodium intake is low aldosterone is high and the kidney conserves sodium.

Chloride acts as the main negatively charged ion and neutralizes the positively charged sodium and potassium ions. Chloride ions are most abundant in the fluid outside cells but some are found inside the cells.

Muscle contraction

The electrolytes and calcium are involved in muscle contraction. They regulate heartbeat through their effects on heart muscle.

Acid-alkali balance

Sodium plays a role in preserving the acid-alkali balance of the body in close relationship with bicarbonate, phosphate, protein, potassium, chloride, calcium and magnesium.

Nerve impulse transmission

The flow of sodium into the nerve cell and the opposite flow of potassium out of the cell sets up an electrical impulse that travels down the nerve.