Cell damage

Cell damage is damage to any of the components of the cell.

Sub-lethal damage
If damage to a cell is minimal, the cell can recover following removal of the damaging stimulus. Damaged proteins and organelles are removed by a cell stress response and autophagy with new structural components being synthesized. This is termed sub-lethal cell damage and is associated with recognizable structural changes.

Sub-lethal damage can be identified from microscopic changes in affected cells. The first evidence of such damage is seen ultrastructurally as swelling of the membrane bound organelles, particularly the endoplasmic reticulum and the mitochondria. There is:


 * Loss of some ribosomes


 * The mitochondria appear swollen
 * The vacuoles push the cristae apart
 * Accumulation of electrolytes and water occurs
 * There is damage to enzymes of the membrane sodium pump

If ATP production is insufficient to maintain function, lethal function is marked by disintegration of other organelles and autolysis proceeds.

Microscopically, these reversible changes caused by swelling of the organelles is reflected in cellular swelling, paleness of cytoplasm and development of small intracellular vacuoles, giving rise to the widely used descriptive terms cloudy swelling and hydropic degeneration.

Lethal damage
Lethal damage leads either to necrosis, or the rather more controlled apoptosis of the cell.

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


 * DNA damage: In human cells, both normal metabolic activities and environmental factors such as UV light and Radiation can cause DNA damage, resulting in as many as 1 million individual molecular lesions per cell per day.
 * Membrane damage: Damage to the cell membrane disturbs the state of cell electrolyte, e.g. calcium, which, when constantly increased, induces apoptosis.