Apoptosis (plural: apoptoses), also known as programmed cell death (PCD) is a term to describe the process of regulated cell death. This is in contrast to necrosis, which is unregulated cell death often secondary to external factors .
Apoptosis occurs in cells which are destined to die by activation of specific genes. These in turn cause activation of intrinsic enzymes causing degradation of cellular DNA and proteins. The cell is then broken down into apoptotic bodies and removed by phagocytes. Apoptosis occurs without breakdown of the plasma membrane and lack of leakage of cellular contents, in contrast to necrosis, preventing an inflammatory response .
Apoptosis can occur in both physiological and pathological scenarios.
Physiologic causes include:
- removal of cells during embryogenesis
- elimination of potentially self-reactive cells, such as T cells in the thymus
Pathologic causes include:
- removal of cells injured beyond repair, for examples cells that have accumulated too much DNA damage
- removal of cells in certain infections, such as virally-infected cells in an effort to prevent further infection