Facts about Cell Death
The most common types of cell death
Essentially applies to morbid cell death caused by factors outside the cell such as toxins, hypoxia, mechanical violence, heat, cold or radiation, but more recently researchers have also observed programmed necrosis. During necrosis, disruptions become so great that a number of processes inside the cell start to malfunction and finally the cell wall cannot remain intact and the cell collapses. The cell contents then leak into the surrounding tissue. The leaked contents cause an inflammation, which further damages adjacent tissue.
Programmed cell death, usually caused by factors inside the cell but sometimes by external factors such as drugs. A genetic program is started which makes the cell shrink in a predictable way; the nucleus shrinks first, then fragments and the whole cell dissolves. The remaining parts are removed by macrophages or adjacent cells. Apoptosis does not cause any inflammation.
From the Greek, meaning "self-eating". The cell breaks down its own worn components by transporting them to lysosomes, which are like small stomachs in the cell, where they are consumed. Autophagy can function both as a cell killing mechanism and a cell saving mechanism. In the former process, the cell eats itself; in the latter, only the damaged components are eaten and replaced with new parts.
This is what kills cancer cells after radiation or drug-induced DNA damage. The genetic damage in the cell nucleus cannot be repaired, cell division does not function and the cell collapses.
Only occurs in women's breasts after breastfeeding has ceased and the milk-producing cells are no longer required. They die through this mechanism.
Cell death diseases
The following are a number of diseases that are wholly or partly caused by imbalance in the cell death process.
Increased cell death
- Alzheimer's disease
- Huntington's disease
- Parkinson's disease
- Aplastic anaemia
- Heart attack
- Type I diabetes
Decreased cell death
- Systemic Lupus Erythematosus (SLE)
- Rheumatoid arthritis
- Down's syndrome
Death receptor: Located on all cells and activates the cell death program inside the cell. The immune system often activates the death receptor of cells infected by a virus so that they die before the virus has time to proliferate.
Death ligands: Molecules that bind to the death receptor and initiate the cell death program.
Decoy death receptor: A death receptor that has no contact with a cascade of events under the cell surface. Used by cancer cells to diminish the effect of death ligands.
Death signal: Occurs when a death ligand binds to a death receptor.
Death genes: Genes that regulate cell death. The first to be detected were ced-3, ced-4 and ced-9 in the worm C. elegans. There are corresponding genes in humans, such as caspase-3, APAF-1 and bcl-2.
Source: Boris Zhivotovsky and National Encyclopaedia. The text was published in Medical Science, issue 2, 2014.