Cell injury

Cell damage can occur as a result of an adverse stimulus which disrupts the normal homeostasis of affected cells. Among other causes, this can be due to physical, chemical, infectious, biological, nutritional or immunological factors. Cell damage can be reversible or irreversible. Depending on the extent of injury, the cellular response may be adaptive and where possible, homeostasis is restored. Cell death occurs when the severity of the injury exceeds the cell’s ability to repair itself. Cell death is relative to both the length of exposure to a harmful stimulus and the severity of the damage caused. Cell death may occur by necrosis or apoptosis.

The most notable components of the cell that are targets of cell damage are the DNA and the cell membrane.

Some cell damage can be reversed once the stress is removed or if compensatory cellular changes occur. Full function may return to cells but in some cases a degree of injury will remain.

Cellular swelling (or cloudy swelling) may occur due to cellular hypoxia, which damages the sodium-potassium membrane pump; it is reversible when the cause is eliminated. Cellular swelling is the first manifestation of almost all forms of injury to cells. When it affects many cells in an organ, it causes some pallor, increased turgor, and increase in weight of the organ. On microscopic examination, small clear vacuoles may be seen within the cytoplasm; these represent distended and pinched-off segments of the endoplasmic reticulum. This pattern of non-lethal injury is sometimes called hydropic change or vacuolar degeneration. Hydropic degeneration is a severe form of cloudy swelling. It occurs with hypokalemia due to vomiting or diarrhea.

The ultrastructural changes of reversible cell injury include:

The cell has been damaged and is unable to adequately metabolize fat. Small vacuoles of fat accumulate and become dispersed within cytoplasm. Mild fatty change may have no effect on cell function; however more severe fatty change can impair cellular function. In the liver, the enlargement of due to fatty change may compress adjacent bile canaliculi, leading to cholestasis. Depending on the cause and severity of the lipid accumulation, fatty change is generally reversible. Fatty Change is also known as fatty degeneration, fatty metamorphosis, or fatty steatosis.

Necrosis is characterised by cytoplasmic swelling, irreversible damage to the plasma membrane, and organelle breakdown leading to cell death. The stages of cellular necrosis include pyknosis; clumping of chromosomes and shrinking of the nucleus of the cell, karyorrhexis; fragmentation of the nucleus and break up of the chromatin into unstructured granules, and karyolysis; dissolution of the cell nucleus. Cytosolic components that leak through the damaged plasma membrane into the extracellular space can incur an inflammatory response.

...
Wikipedia