Life depends on many complex and highly regulated chemical reactions, all of which occur in water. Many of these reactions are catalyzed by enzymes that can function onlywithin a narrow range of conditions. Changes in the total amount of water, the pH, or the concentration of specific electrolytes can alter chemical reactions on which life depends. Homeostasis requires the maintenance of these parameterswithin a narrow range of values, and failure to maintain homeostasis can result in illness or death.

The kidneys, along with the respiratory, integumentary, and gastrointestinal systems, regulate water volume, electrolyte concentrations, and pH. The nervous and endocrine systems coordinate the activities of these systems.

This chapter covers body fluids (p. 1006), the regulation of body fluid concentrationand volume (p. 1007), the regulation of intracellular fluid composition (p. 1012), the regulation of specific electrolytes in the extracellular fluid (p. 1013), and the regulation of acid - base balance (p. 1022).