Necrosis is defined as the death of a fragment of a living organism under the influence of such damaging factors as trauma, ischemia, hypoxia, toxins, chemical agents, bacteria, viruses, radiation, as well as low or high temperature. What are the causes and types of necrosis? Which tissues are most often affected?
Necrosis( necrosis ) is characterized by the fact that it can affect both cells selectively and cells of a given area of the body. In addition, it stimulates the inflammatory response of neighboring cells, which results in phagocytosis and removal of necrotic masses.
Necrosis: what changes take place in the cell?
The following changes occur microscopically in the cell - initially it increases in size, the mitochondria swell, the cell nucleus gradually dissolves, due to disruption of the ion pump in the cell, sodium and water accumulate, cell organelles disintegrate. In the final stage, the cell dissolves.
Macroscopically dead tissue is homogeneous, dull and yellowish. What's more, its color may change if putrefactive processes additionally occur.
Thrombotic necrosis
The most common type of necrosis is thrombotic necrosis, which is the result of tissue ischemia. It is typical of infarctions in all solid organs except the brain. As a result of the damaging factor, the structural and enzymatic proteins of the cell are denatured.
Additionally, a gradual disintegration of the nucleus and cytoplasmic organelles as a result of enzymatic catabolism can be observed.
This necrosis is characterized by the presence of long-lasting shadows of dead cells in the form of eosinophilic bands or spheres. Probably the process of protein coagulation takes place here in a highly acidified environment, which translates into inhibition of the lytic activity of enzymes.
This condition usually lasts for several days, after which the dead tissue begins to absorb more and more water and becomes fragmented. Leukocytes appear at the site of necrosis, and the enzymes present in their lysosomes lead to the digestion of dead cells. In the next step, macrophages remove dead cell masses by phagocytosis.
Slush
In diffuse necrosis, as a result of enzymatic digestion of cells and tissues, dead tissue is transformed into a dense mass. This necrosis concerns cells of the central nervous system damaged due to oxygen deficiency.
It can also occur in the course of viral hepatitis, in the mucosa (especially of the stomach and duodenum - it precedes the ulcer formation) and in local bacterial and fungal infections, as these microorganisms are a strong stimulus that attracts inflammation cells.
Dissolved dead tissue is finally removed by phagocytes. However, it very often happens that the process of necrosis is initiated by acute inflammation - then the formed dead tissue is mixed with a large amount of neutrophils and has the form of a yellow goo, commonly known as pus.
Cheese necrosis
Cheese necrosis is a specific type of thrombotic necrosis that occurs in the course of diseases such as:
- tuberculosis
- syphilis
- Hodgkin
- some cancers
It is produced in cell-rich, non-vascularized or poorly vascularized tissues and those treated with toxins.
The name "cheesy" results from the macroscopic appearance of necrosis, which takes the form of white, brittle masses similar to white cheese. Microscopically, the areas of necrosis consist of fragmented or dissolved cells with a granular amorphous structure.
The necrotic tissue is completely destroyed - the contours of the cells cannot be distinguished. Additionally, in the course of tuberculosis there is granulation tissue, while in syphilis, the necrotic masses are less fragile due to incomplete digestion of elastic vascular fibers.
Enzymatic necrosis
The enzymatic necrosis of adipose tissue most often concerns the parapancreatic adipose tissue and is most often formed in the course of acute pancreatitis.
The activated pancreatic enzymes are then released from the glandular cells and pancreatic ducts, which lead to the digestion of the pancreatic parenchyma and the surrounding adipose tissue.
The fatty acids released from adipose tissue bind with calcium, which leads to the formation of very characteristic chalky-white areas (the so-called saponification process).
In addition, there may be inflammatory infiltrates and bloody effusions in this necrosis.
Zgorzel (gangrene)
Gangrene, otherwise known as gangrene, is necrosis in which the rotting process takes place. It develops as a result of infection with anaerobic bacteria of the genus Clostridium. Stands outtwo types of gangrene - dry and wet.
In dry gangrene, ischemic, necrotic tissue is mummified (dehydrated) - this requires appropriate environmental conditions, and more specifically dry air and its appropriate humidity.
Necrotic tissue is initially pale and then turns black due to the presence of iron sulphides formed in the process of rotting. An example of dry gangrene is very common in people with advanced diabetes, the so-called diabetic foot.
It is caused by atherosclerosis and microangiopathy, which result in ischemia. In addition, super-contamination with putrefactive bacteria is very quickly added.
Damp gangrene is formed in tissues that are very moist, warm and in contact with the external environment (e.g. intestines, lungs, skin). It occurs in the form of gangrene of the intestine in the course of its twisting or gangrene of the dental pulp.
For example, in the twist of the intestines, the outflow of venous blood is blocked, and the arterial blood is still supplied. Eventually, hemorrhagic necrosis develops and the anaerobic bacteria present in the gut initiate the rotting process.
A specific type of gangrene is gas gangrene, which occurs mainly in dirty lacerated wounds. It is caused by bacteria capable of producing gas -Clostridium perfringens ,Clostriudium oedematiensandClostridium oedematis maligni .
The resulting gas spreads through the tissue in the form of bubbles - this accelerates the spread of gas gangrene. Interestingly, the subcutaneous tissue and muscles are full of bubbles of putrid gas and bloody exudate. The occurrence of crackling under pressure is also characteristic here.
Fibrous necrosis
The last type of necrosis is fibrinous necrosis. It occurs as a result of specific immune reactions in which antigen-antibody complexes build up in the arterial wall. This happens in the course of many autoimmune diseases, including polynodular arteritis.
This type of necrosis is characterized by the presence of fibrinoid - an amorphous, pale pink structure, which is a deposit consisting of immune complexes and fibrin emerging from the lumen of the blood vessels.