ABSTRACT
Total body water (TBW) represents about 60% of the body weight of a young adult male. The distribution of this fluid across the primary fluid spaces is depicted in Figure 6.
Physiology
Intracellular fluid (ICF) is separated from extracellular fluid (ECF) by a cell membrane that is highly permeable to water but not to most electrolytes. Intracellular volume is maintained by the membrane sodium-potassium pump, which moves sodium out of the cell (carrying water with it) in exchange for potassium. Thus, there are significant differences in the electrolytic composition of intracellular and extracellular fluid.
