ABSTRACT
The human body can be likened to a sac of electrolyte-rich fluids in which is suspended or dissolved a complex network of solids known collectively as ‘‘organs.’’ The common medium of these fluids is water; the electrolytes are a mixture of primarily monovalent and divalent ions. The total volume of water, known as total body water, accounts for approximately 60% of total body mass. Substances are continually added to and excreted from this aqueous environment, and only through a system of homeostatic, protective mechanisms is the composition and distribution of this fluid-based system maintained. Disease, pharmaceuticals, and medical interventions all have the potential to disrupt the balance of this fluid medium and result in clinically evident fluid and electrolyte disturbances. To achieve the desired goal of preventing or treating such disturbances, the nature, composition, and interrelationships of these fluids and the homeostatic mechanisms that maintain them must be clearly understood.
