The intracellular fluid differs significantly from the
extracellular fluid; for example, it contains large amounts
of potassium, magnesium, and phosphate ions instead of
the sodium and chloride ions found in the extracellular
fluid. Special mechanisms for transporting ions through
the cell membranes maintain the ion concentration differences
between the extracellular and intracellular fluids.
These transport processes are discussed in Chapter 4.