From an agression, the cell can respond in three ways: adaptation, reversible injury and irreversible damage. These mechanisms will be further detailed in the topics of their themes, but basically, the adaptation occurs by changing the volume, number and / or cell differentiation, while the reversible lesion is characterized by degeneration and the irreversible lesion by damages to the cell death.

The cell may suffer aggression by several factors. Among them, the main offenders are:

• Physical agents

• Chemicals agents

• Immunological changes

• Genetic disorders

• Nutritional disorders

• Hypoxia