The normal cell maintains a steady state, termed homeostasis, in which the internal milieu of the cell is kept within physiological parameters. The response of a cell to any change in its environment constitutes the pathophysiological basis of clinical symptoms. When cells are faced with physiological or pathological stress they respond in several ways, collectively known as cellular adaptation. When the capacity of the cell to adapt is exceeded, then the cell undergoes a series of changes referred to as cell injury. The degree of injury dictates whether the cell will recover (i.e. reversible cell injury) or progress to cell death (i.e. irreversible cell injury). The effect on the tissue will depend on the duration of the injury, the nature of the injurious agent, the proportion and types of cells affected and the ability of the tissue to regenerate.