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 hydrophobic degeneration.