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Apoptosis and necrosis


Cell death
Cells die by one of two mechanisms necrosis or
apoptosis
Two physiologically different processes
Necrosis death by injury
Apoptosis death by suicide
Apoptosis and necrosis have different characteristics

Necrosis

Death by accident
Associated with nonphysiological circumstances that
disrupt cellular homeostasis (eg., ischemia, hypoxia and
poisoning)
Necrosis is caused by membrane dissolution (osmotic lysis,
shear stress, pore-forming proteins, loss of ATP)
Necrosis is bad because cellular material (including
degradative enzymes) is released into surrounding tissue
Affects contiguous groups of cell
Necrosis usually causes inflammatory reaction

Necrosis begins with an impairment of the cell s ability to maintain homeostasis, leading
to an influx of water and extracellular ions. Intracellular organelles, most notably the
mitochondria, and the entire cell swell and rupture (cell lysis). Due to the ultimate breakdown
of the plasma membrane, the cytoplasmic contents including lysosomal enzymes
are released into the extracellular fluid. Therefore, in vivo, necrotic cell death is often
associated with extensive tissue damage resulting in an intense inflammatory response5.
Apoptosis, in contrast, is a mode of cell death that occurs..