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Cytolysis is the lysis, or death, of cells due to the rupture of the cell membrane. Cytolysis is caused by excessive osmosis, or movement of water, towards the inside of a cell. The cell membrane cannot withstand the osmotic pressure of the water inside, and so it explodes. Osmosis occurs from a region of high-water potential to a region of low-water potential passing through a semipermeable membrane.

Cause and effects

Osmotic lysis occurs in a hypotonic environment, where water diffuses into the cell. As the water continues to diffuse into the cell, the cell grows larger, and will eventually burst if too much water enters. The cell membrane is not strong enough to prevent and stop the swelling of the cell, and eventually will rupture, releasing the cell contents.

Cytolysis does not occur in plant cells because plant cells have a strong cell wall that contains the osmotic pressure, or turgor pressure, which would otherwise cause cytolysis to occur. Contrary to organisms without a cell wall, plant cells must be in a hypotonic environment in order to have this turgor pressure, which provides the cells more structural support, preventing the plant from wilting. In a hypertonic environment, plasmolysis occurs, which is nearly the complete opposite of cytolysis: Instead of expanding, the cytoplasm of the plant cell retracts from the cell wall, causing the plant to wilt.

Osmotic lysis is often the result of a stroke, since a stroke leads to a malfunctioning of the cell's metabolism, which results in an inflow of extracellular fluid into the cell.

The Fab portion of IgG or IgM binds to epitopes on the outer membrane of the gram-negative cell wall. This activates the complement pathway enabling the [membrane attack complex]? (MAC) to insert through the outer membrane and cytoplasmic membrane causing the bacterium to lyse.

Preventing osmotic lysis

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.

Other organisms pump solutes out of their cytosol, which brings the solute concentration closer to that of their environment and slows down the process of water's diffusion into the cell, preventing cytolysis. If the cell can pump out enough solutes so that an isotonic environment can be achieved, there will be no net movement of water.