For every cell, there is a time to live and a time to die.
There are two ways in which cells die:
they are killed by injurious agents
they are induced to commit suicide
Death by injury
Cells that are damaged by injury, such as by mechanical damage or exposure
to toxic chemicals undergo a characteristic series of changes:
they (and their organelles like mitochondria) swell (because the ability
of the plasma membrane to control the passage of ions and water is disrupted)
the cell contents leak out, leading to inflammation of surrounding tissues
Death by suicide
Cells that are induced to commit suicide show the following characters:
have their mitochondria break down with the release of
The pattern of events in death by suicide is so orderly that the process
is often called programmed cell death or PCD. The cellular machinery of
programmed cell death turns out to be as intrinsic to the cell as, say,
mitosis. Programmed cell death is also called apoptosis.
develop bubble-like blebs on their surface
have the chromatin (DNA and protein) in their nucleus degraded
break into small, membrane-wrapped, fragments
the phospholipid phosphatidylserine, which is normally hidden within the
plasma membrane is exposed on the surface. This is bound by receptors on
phagocytic cells like macrophages and dendritic cells which then engulf
the cell fragments.
The phagocytic cells secrete cytokines that inhibit inflammation.