Sodium
Sodium is the most abundant extracellular fluid cation and regulates serum (extracellular) osmolarity, as well as nerve impulse transmission and acid-base balance. Potassium is the major intracellular osmolarity regulator, and it also regulates metabolic activities, transmission and conduction of nerve impulses, cardiac conduction, and smooth and skeletal muscle contraction. Chloride is a major extracellular fluid anion and follows
sodium. Calcium is an extracellular cation necessary for bone and teeth formation, blood clotting, hormone secretion, cardiac conduction, transmission of nerve impulses, and muscle contraction.