Apoptosis

Apoptosis describes the programmed cell death, the deliberate suicide of a cell in a multicellular organism for the greater good of the whole individual. In contrast to necrosis?, apoptosis occurs naturally during development, for example, the differentiation of human finger?s requires the cells in between the fingers to initiate apoptosis so the fingers can separate.

Apoptosis also occurs when a cell is damaged beyond repair, or infected with a virus. The "decision" for apoptosis can come from the cell itself, or from a call that is part of the immune system. If the apoptosis program of a cell itself is damaged (by mutation), or if the initiation is blocked (by a virus), a damaged cell can start growing without restrictions, developing into cancer.

Programmed cell death is an integral part of vertebrate tissue development, and it does not elicit the inflammatory reponse which is charasteristic of necrosis?. In other words, apoptosis does not resemble the sort of reaction when tissue is damaged either as a result of accident or of pathogenic infection. Instead of swelling and bursting --and, hence, spilling their internal contens into extracellular space--, apoptotic cells and their nucleus shrink, and often fragment. In this way, they can be efficiently phagocytosed (and, as a consequence of this, their components reused) by macrophages or by neighgoring cells.

See also: Immunology -- Biochemistry

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