Osmolarity and partitioning of fluids

The body is composed of cells bounded by membranes. Cell function depends on the maintenance and function of transmembrane potentials and these in turn are determined by the distribution of ions across the membrane. One of the factors affecting this distribution is osmotic pressure. Electrolytes, which are small charged particles, are unable to pass through cell membranes except via carrier proteins, whose function may or may not involve the expenditure of metabolic energy. Inequalities in osmotic pressure across a membrane (e.g. intra/extracellular) result in free passage of water across the membrane until the osmotic pressures are equal. This results in shrinkage or swelling of the cell.