Considering cells can't survive outside a narrow range of electrolyte levels in the extracellular fluid, the ability to retain salt and at the same time excrete excess salt is very important.

考虑到细胞无法在细胞外液中电解质水平范围较窄的情况下存活，在保留盐的同时排出多余盐的能力就显得至关重要。