ApoptosisProgrammed cell death

Apoptosis is cell suicide by design. The cell shrinks, its contents are packaged neatly, and neighbouring cells clear the fragments without triggering inflammation — quite unlike necrosis, where a cell bursts and provokes an immune response.

It matters because it is essential maintenance. It removes cells with irreparable DNA damage before they can become cancerous, sculpts tissue during development, and clears worn-out immune cells. Failure of apoptosis is a hallmark of cancer; excessive apoptosis contributes to neurodegeneration and to muscle loss with age.

In practice it sits alongside autophagy as one of the two quality-control systems that keep tissue healthy — autophagy recycling components within a cell, apoptosis removing the cell entirely when that is not enough.