hypertonic

Hypertonic describes a solution with a higher concentration of dissolved substances than another solution or the cytoplasm of a cell. In biology, tonicity refers to a solution’s effect on cell volume; hypertonic solutions have a higher effective osmolarity relative to the cell interior, causing water to move out of the cell by osmosis.

In animal cells, exposure to a hypertonic environment leads to loss of water and cell shrinkage (crenation). In plant cells, water loss causes the plasma membrane to pull away from the cell wall in a process called plasmolysis, while the cell wall remains intact. Hypertonic conditions can also affect microorganisms, sometimes inhibiting growth unless the organisms adapt by accumulating compatible solutes.

Hypertonic solutions are used in medicine and biology. For example, hypertonic saline solutions (greater than about 0.9% NaCl) draw water from swollen tissues and are used in specific clinical situations, such as treatment of intracranial edema and hyponatremia, under careful supervision. The concept of tonicity helps distinguish the practical effect on cells from the total solute concentration of a solution; a solution can be hyperosmotic yet have a reduced tonicity effect if some solutes cross the membrane readily.

In ecology and industry, hypertonic environments can inhibit microbial growth or preserve foods through high salt concentrations. Some microorganisms, such as halophiles, thrive in naturally hypertonic environments, while others avoid such conditions. Overall, hypertonic refers to a higher-solute environment that tends to draw water out of cells, altering cell volume and physiology depending on membrane properties and solute permeability.