Body fluid compartments

Functionally, the total body water can be subdivided into two major fluid compartments called the extracellular and the intracellular fluid compartments. Extracellular fluid (ECF) consists mainly of the plasma found in the blood vessels and the interstitial fluid (IF) that surrounds the cells (Table 43-2). In addition, the lymph and so-called transcellular fluid (TF)—such as cerebrospinal fluid, joint fluids, and humors of the eye—are also considered extracellular fluid. The distribution of body water by compartment is shown in Figure 43-1. Intracellular fluid (ICF) refers to the water inside the cells. Extracellular fluid makes up the internal environment of the body. It therefore serves the dual vital functions of providing a and transporting substances to and from them. Intracellular fluid, on the other hand, because it is a solvent, func-tions to facilitate intracellular chemical reactions that maintain life. When compared according to volume, intracellular fluid is the largest (25 L), plasma the smallest (3 L), and interstitial fluid in be-tween (12 L). Figure 43-2 illustrates the typi-cal normal fluid volumes in a young adult male, and Table 43-1 lists volumes of the body fluid com-partments for both sexes as a percent-age of body weight.