Jump to: navigation, search 23:30, 3 October 2007 (UTC)

Isotonic Fluid

Fluid that has the same concentration of solutes (osmolality) as body fluids.

For Isotonic muscle exercise, see Isometric exercise and Weight training.
For the term associated with muscle contraction, see isotonic (exercise physiology)
For the term in nuclear physics, see isotone

Isotonic literally translates to equal tension. The term is used in several different contexts.

Isotonic solution bears the same chemical resemblance of the body’s blood, plasma and tears. All fluids in the body have a certain concentration, referred to as osmotic pressure. The body’s common osmotic pressure, which is isotonic, allows a consistent maintenance of body tissues. In order for a substance to be absorbed and used in the body’s metabolism, it must be transported in an isotonic state.

Cell biology

Effect of different solutions on blood cells

Cells have a semipermeable membrane that allows the diffusion (flow) of water, but not the dissolved compounds such as salt ions (solutes). Water diffuses across the membrane in direction of the higher concentrated solution in a process called osmosis, thereby generating osmotic pressure if the inside concentration is higher. Plant cells often rely on this osmotic pressure for structural support. Under isotonic conditions the concentrations of impermeable solutes, the osmolality, is the same inside and outside the cell and there is no osmotic pressure. A medium of lower osmolality is called hypotonic and one of higher osmolality is called hypertonic.


An isotonic solution that mimicks the osmolality of blood for humans and many other mammals consists of 0.9% (9 g/L) sodium chloride in water and is often referred to as saline. Saline is generally administered via an intravenous drip. Red blood cells will not change their form in such an isotonic medium while they would swell and even burst in pure water.


This term is also used in relation to a sports drink with added salts mimicking the osmolality of blood. This property is claimed by their advertising campaign to increase physical endurance. The statistically insignificant (6 rowers) scientific study often quoted, however, attributes the 10% increase in endurance over water to the higher carbohydrate content.[1]

See also

de:Isotonisch nl:Isotoon nds:Isoton (Karnphysik) sv:Isoton