4.3 Composition of body fluids
Electrolytes and Nonelectrolytes
Nonelectrolytes have bonds (usually covalent bonds) that
prevent them from disassociating in a solution. Because of this, no
electrically charged species are created when nonelectrolytes dissolve in
water. Most nonelectrolytes are organic molecules — lipids, glucose, urea,
creatinine, for example.
In contrast, electrolytes are
chemical compounds that do disassociate into ions in water. Since ions are
charged particles, they can conduct an electrical current — that’s why they’re
called electrolytes! For the most part, electrolytes include organic salts,
some proteins, and both organic and inorganic acids and bases.
Electrolytes have much greater osmotic
power than nonelectrolytes because each electrolyte molecule disassociates into
at least two ions. For instance, a molecule of sodium chloride (NaCl)
contributes twice as many solute particles as glucose, and a molecule of
magnesium chloride (MgCl2) contributes three times as many.
Regardless of the type of solute particle,
water always moves according to osmotic gradients — from an area of lesser
osmolarity to an area of greater osmolarity. For this reason, electrolytes have
the greatest ability to cause fluid shifts.