Apoptosis

Apoptosis is a process of programmed cell death in which body cells die and get absorbed (phagocytosed) under genetic control. Here cell’s own gene plays an active role on its death, therefore, also called as cell suicide.
Mechanism. Apoptosis may be initiated by:
(i) environmental processes such as inflammation
(ii) internal stimuli by some genes

(iii) Fas, a transmembrane protein produced by natural killer cells  and T-lymphocyes
(iv) Tumour necrosis factor.
The ultimate pathway initiating apoptosis is activation of group of cysteine proteases inactivate enzymes (together called as, Caspases) within the mitochondria. The activated apoptotic gene causes the cell to undergowo DNA fragmentation, condensation of cytoplasm and chromatin; finally the cell break up and remnants are removed by phagocytes.
2. Physiological significance. Apoptosis plays an 3 important role during embryonal development and also in adulthood. It removes un-needed cells. For example,
(i) it is responsible for regression of duct system during sex differentiation in the foetus;
(ii) it is responsible for degeneration and regeneration of neurons within the CNS and for the formation of synapse;
(iii) it is responsible for removal of inappropriate clones of immune cells;
 (iv) it is responsible for cyclical shedding of endometrium at the time of menstruation; and
(v) it is responsible for cell shed from the tip of the villi in the small intestine. GIT
3. Applied. Abnormal apoptosis occurs in autoimmune diseases , degenerative diseases and cancers.