Osmosis

he diffusion of pure solvent across a membrane in response to a concentration gradient, usually from a solution of lesser to one of greater solute concentration. adj., adj osmot´ic.

The process of osmosis and the factors that influence it are important clinically in the maintenance of adequate body fluids and in the proper balance between volumes of extracellular and intracellular fluids.

The term osmotic pressure refers to the amount of pressure necessary to stop the flow of water across the membrane. The hydrostatic pressure of the water exerts an opposite effect; that is, it exerts pressure in favor of the flow of water across the membrane. The osmotic pressure of the particles in a solute depends on the relative concentrations of the solutions on either side of the membrane, and on the area of the membrane. The osmotic pressure exerted by the nondiffusible particles in a solution is determined by the numbers of particles in a unit of fluid and not by the mass of the particles.

the top layer is the high non water cell

middle is cell free

low is water free cell