Apoptosis

Why do cells commit apoptosis? There seem to be two major reasons. First, apoptosis is one means by which a developing organism shapes its tissues and organs. For instance, a human fetus has webbed hands and feet early on its development. Later, apoptosis removes skin cells, revealing individual fingers and toes. A fetus's eyelids form an opening by the process of apoptosis. During metamorphosis, tadpoles lose their tails through apoptosis. In young children, apoptosis is involved in the processes that literally shape the connections between brain cells, and in mature females, apoptosis of cells in the uterus causes the uterine lining to slough off at each menstrual cycle.

Cells may also commit suicide in times of distress, for the good of the organism as a whole. For example, in the case of a viral infection, certain cells of the immune system, called cytotoxic T lymphocytes, bind to infected cells and trigger them to undergo apoptosis. Also, cells that have suffered damage to their DNA, which can make them prone to becoming cancerous, are induced to commit apoptosis.