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Blood cells in solutions with different osmotic pressure. Cytolysis would result in the image on the far right.
Micrographs of osmotic pressure on red blood cells
A human white blood cell (upper right) in water swells until it bursts (at ~13 seconds)

Cytolysis, or osmotic lysis, occurs when a cell bursts due to an osmotic imbalance that has caused excess water to move into the cell. It occurs in a hypotonic environment, where water moves into the cell by osmosis and causes its volume to increase to the point where the volume exceeds the membrane's capacity and the cell bursts. The presence of a cell wall prevents the membrane from bursting, so cytolysis only occurs in animal and protozoa cells which do not have cell walls.

In mammals[edit]

Osmotic lysis is often one result of a stroke, because of improper nutrient perfusion and waste removal alter cell metabolism. Such malfunction results in an inflow of extracellular fluid into the cells.

In bacteria[edit]

Osmotic lysis would be expected to occur when bacterial cells are treated with a hypotonic solution with added lysozyme, which destroys the bacteria's cell walls.


Different cells and organisms have adapted different ways of preventing cytolysis from occurring. For example, the paramecium uses a contractile vacuole, which rapidly pumps out excessive water to prevent the build-up of water and the otherwise subsequent lysis.[1] Additionally, these protists have cell membranes which are less permeable to water than some other species.[1]


See also[edit]


  1. ^ a b Campbell, Neil A.; Reece, Jane B.; Urry, Lisa A.; Cain, Michael L.; Wasserman, Steven A.; Minorsky, Peter V.; Jackson, Robert B. (2009). Biology (9th ed.). p. 134. ISBN 9780321558237.