Homeostasis I: Eating & drinking
Water and sodium balance maintenance. Although the composition of
intracellular and extracellular fluid is different, the osmolalities are
identical under normal conditions and during normal water deprivation. When Na+ ions are depleted in the extracellular fluid, however (as is the case when you sweat severely), Na+ ions do not leave the intracellular space to compensate. H2O molecules move toward the region of greater Na+ concentration to maintain osmolarity, resulting in edema (swelling) of cells, with potentially harmful or fatal consequences.