1. Apoptosis

2. Apoptosis
There are two forms of cell death
 Programmed death of cells called Apoptosis.
 An uncontrolled death of cells called Necrosis.

3.  Both apoptosis and necrosis occur under different circumstances and involve different steps.
 The term apoptosis is derived from the Greek word meaning dropping or falling off. It was
first introduced by Kerr, Wyllie, and Currie.
 Apoptosis is a biological process which occurs in all multicellular organisms including plants
and animals. It removes the cells from the organisms that should no longer be a part of the
organism. This process plays a major role in the development of humans and in developing
and maintaining a healthy immune system.
 On an average, 50 – 80 billion cells die every day in a human adult due to apoptosis. During
this biological process, infected cells, pre-cancerous cells and other cancer cells are
eliminated successfully and maintain the balance of cells in the human body. Therefore, it is
an essential process that is responsible for the normal development of cells, cell cycle
maturation and maintaining the regular functions and activities of cells.
 Apoptosis occurs in all the vertebrates that have fingers and toes like digits. A slight mistake
during apoptosis results in fused toes or fingers. The loss of the tail of a tadpole when it
develops into a frog is yet another example of apoptosis.

4. Apoptosis Pathways
The process of apoptosis undergoes two pathways:
1. Extrinsic Pathway
2. Intrinsic Pathway

5. 1-Extrinsic Pathway
 This pathway triggers apoptosis in response to external stimuli, like, ligand
binding at death receptors on the cell surface. These receptors are members
of the Tumor Necrosis Factor gene family. The receptor binding initiates
caspase activation.

6. Intrinsic Pathway
 This pathway triggers apoptosis in response to internal stimuli such as
biochemical stress, DNA damage and lack of growth factors.
 This pathway is modulated by two groups of molecules- Bax, and Bcl-2.
 These groups of molecules determine whether a cell will survive or undergo
apoptosis in response to the stimuli.

7. Significance of Apoptosis
Apoptosis is significant for the following reasons:
 It helps to maintain homeostasis in the multicellular organisms.
 Proper size of the body is maintained by apoptosis.
 Apoptosis maintains the constancy of cell number in an organism.
 The unwanted cells are eliminated from the body by apoptosis.
 The dangerous T-lymphocytes are eliminated by apoptosis.
 Programmed cell death is crucial for cell development.

8. Role Of Apoptosis
Apoptosis plays an important role in the body of an organism. Following are a few
such roles performed by the process:
 The separation of the fingers during the development of the foetus is due to
apoptosis.
 It results in the closure of the neural tube in the dorsal part.
 Programmed cell death results in the removal of vestigial remnants such as
pronephros.
 During the determination of sex of the foetus, the Wolffian ducts are removed
by cell death.
 In the urachus, apoptosis allows the removal of redundant tissues between
the bladder and umbilicus.