Necrosis consists of death of a tissue, organ or group of cells that make up a living organism. Necrosis occurs when there is a lack of blood supply to the cells, causing them to deteriorate.
There can be several reasons for the appearance of necrosis, whether through physical agents (injuries, hypothermia, radiation, etc.); chemical agents (exposure to toxic substances, drugs, poisons, etc.); biological agents (bacterial, viral, parasitic infections, etc.); and circulatory failure (from vasoconstrictions and infarctions, for example).
Regardless of the cause, necrosis appears when the cells that make up the tissue at the site suffer an irreversible damage, ceasing all their organic and metabolic functions.
The last stage of necrosis is when the cell nucleus disappears completely. However, before reaching this final step, cells undergo other serious microscopic phenomena, known as pyknosis (core reduction), kariorhexis (irregular chromatin and loss of nuclear limits) and caryolysis (disappearance of the nucleus and chromatin).
Macroscopically, the first signs of necrosis are often blackening and loss of tissue sensitivity. In some types of necrosis, when diagnosed early enough, they can be treated so that the affected tissue can be recovered or removed and replaced by another that is healthy. However, when bone cells necrose, the only alternative is usually amputation of the necrotic limb.
The origin of this word is in the Greek necrosis, which literally means "death" or "mortification".
Types of necrosis
These are some of the main types of necrosis:
- Coagulation necrosis: also known as "ischemic necrosis", it is the lack of blood supply to the organic tissue. Occurs due to blood loss.
- Liquefaction necrosis: it occurs in cerebral infarctions and infections, mainly bacterial. It occurs in an inflammatory process in the affected tissue and, consequently, the appearance of leukocytes that try to attack invading microorganisms. Pus usually form in the necrotic area as a result of phagocytization of dead cells.
- Caseous necrosis: a type of necrosis common in tuberculosis cases. The fabric is characterized by having a whitish and yellowish appearance, similar to a cream cheese.
- Fibrinoid necrosis: common in diseases that are autoimmune, such as lupus, rheumatoid arthritis and rheumatic fever, for example.
- Gangrenous necrosis: occurs when a limb loses its blood supply and dies. The fabrics look like "mummy skin", dry and hard. They give off a putrid odor, with the formation of gas bubbles.
Necrosis and Apoptosis
Both are types of cell death, however, unlike necrosis, apoptosis is the programmed cell death. The big difference is that necrosis is always formed through pathological consequences, while apoptosis can arise as a consequence of normal physiological processes of the body.