Peter S. Aronson, Walter F. Boron, Emile L. Boulpaep
The cells of the human body live in a carefully regulated fluid environment. The fluid inside the cells, the intracellular fluid (ICF), occupies what is called the intracellular compartment, and the fluid outside the cells, the extracellular fluid (ECF), occupies the extracellular compartment. The barriers that separate these two compartments are the cell membranes. For life to be sustained, the body must rigorously maintain the volume and composition of the intracellular and extracellular compartments. To a large extent, such regulation is the result of transport across the cell membrane. In this chapter, we discuss how cell membranes regulate the distribution of ions and water in the intracellular and extracellular compartments.