Two liquids are isotonic when they have the same osmotic pressure with the same concentration of dissolved substances , for example mineral salts . The isotonic is the intermediate state between solutions hypertonic and hypotonic. It makes it possible to achieve the hydrosaline balance in an organism.
A solution is isotonic when it has the same osmotic pressure as another solution, especially one in a cell or body fluid.
A muscle contraction is isotonic when the force remains constant. An isotonic contraction is said to be concentric when the muscle contracts while shortening or eccentric when the muscle contracts while lengthening.
An isotonic solution is a solution in which the solvent concentration is equal to the concentration of solute of a cell. In this case, the cell neither swells or shrinks because there is no concentration gradient of water across the cell membrane. Water molecules diffuse through the plasma membrane in both directions, and the rate of diffusion of water is the same in each direction of that cell without gaining or losing water.
An iso-osmolar solution can be hypotonic if the solute is able to penetrate the cell membrane. For example, an iso-osmolar urea solution is hypotonic to red blood cells, causing them to lysis. This is due to the urea entering the cell down its concentration gradient followed by the water. For example, the osmolarity of normal physiological saline , 9 grams of NaCl dissolved in water for a total volume of one liter, is a good approximation of the osmolarity of NaCl in blood, it is blood. Both sodium and chloride ions cannot pass freely through the plasma membrane as opposed to urea.
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