Cell death: necrosis and apoptosis

All living cells become old and die. Death is classified two ways: apoptosis is regulated cell death, and necrosis is accidental cell death due to injury.

Necrosis is caused by external factors such as infection, toxins, trauma and injury. Its cellular changes run in a sequence: karyopyknosis, shrinkage of the nucleus with chromatin condensing; karyorrhexis, fragmentation of the nucleus; karyolysis, complete dissolution of chromatin due to loss of DNA.

Apoptosis is the regulated process by which unneeded and defective cells are eliminated, and it is usually beneficial: cancerous and virus-infected cells get eliminated, and the balance of cells in the body is maintained.

The single best discriminator is volume. A necrotic cell swells and its membrane is damaged; an apoptotic cell shrinks and its membrane blebs but stays intact.

All living cells become old and die.

• Regulated cell death is apoptosis.
• Accidental cell death due to injury is necrosis.

Necrosis is cell death caused by external factors, such as infection, toxins, trauma and injury.

Three changes, and they are a sequence rather than a list. Each is a further stage of the same nucleus falling apart.

The three names share the stem karyo-, meaning nucleus, and differ only in what is done to it: shrunk, broken, dissolved.

Apoptosis is the regulated process by which unneeded and defective cells are eliminated.

It is usually a beneficial process:

• cancerous and virus-infected cells get eliminated;
• it maintains the balance of cells in the human body.

• Loss of mitochondrial function and caspase activation, leading to degradation of proteins. Caspase activation is a process that ensures the cellular components are degraded.
• Fragmentation of DNA.
• Shrinkage of nuclear and cell volume, by destruction of cytoskeleton and chromatin.
• The plasma membrane undergoes shape changes, called blebbing.

This is the table to be able to reproduce under questioning.

Two rows carry most of the discrimination. Swelling against shrinkage, and damage to the membrane against blebbing of an intact one. A necrotic cell bursts and spills its contents, which is why necrosis provokes inflammation; an apoptotic cell packages itself up, which is why apoptosis does not.