Fluid Balance:
The state of the body in relation to the intake and excretion of water and electrolytes, particularly sodium and potassium. It exists in a metabolic balance internally with BODY FLUID COMPARTMENTS, total BODY WATER; BLOOD VOLUME; EXTRACELLULAR SPACE; etc., externally through sensible and insensible SWEATING. The hypothalamus controls water balance. (Dorland, 27th ed; Mountcastle, Medical Physiology, 14th ed, 1980, p1152)
