Chloride is the major anion found in the fluid outside of cells and in blood. An anion is the negatively charged part of certain substances such as table salt (NaCl) when dissolved in liquid. Sea water has almost the same concentration of chloride ion as human fluids.
The balance of chloride ion (Cl-) is closely regulated by the body. Significant decreases in chloride can have deleterious or even fatal consequences. Chloride is normally lost in the urine, sweat, and stomach secretions. Excessive loss can occur from heavy sweating, vomiting, and adrenal gland and kidney disease.