1.2 - Introduction to Cellular Injury and Death

Cell injury begins as reversible injury. If the damage crosses a critical threshold, the injury becomes irreversible and the cell dies. The two major forms of cell death are necrosis and apoptosis.

reversible injury

significant cellular structural or functional abnormality in which the cell has not yet passed the irreversible threshold

• if injury is removed, cell can return to homeostasis

irreversible injury

damage so severe that cell recovery is no longer possible

• hard and fast, unalterable pathway to cell death

• hallmarks of irreversible injury:

  • inability to reverse mitochondrial dysfunction → energy failure

  • profound disturbance of cell membrane function → causes ion imbalance, water movement, leakage of intracellular substances, loss of cellular integrity

necrosis

pathologic, disorderly cell death associated with membrane destruction and inflammation

• membrane damage allows cellular contents to leak

• lysosomal enzymes contribute to digestion of cell

• leaked contents stimulate inflammation

• always pathologic

  • examples — microbial injury, chemical injury, physical injury

apoptosis

regulated programmed cell death in which cellular material is packaged and removed with minimal inflammation

• nuclear dissolution without loss of membrane integrity

• physiologic → normal developmental or tissue-regulation process

  • example — development of teeth and craniofacial structures requires cells in certain locations to disappear so structures can properly form and fuse

• pathologic → severe DNA damage or nutritional deprivation