Necrosis:
The morphologic appearance of necrosis as well as necroptosis is the result of denaturation of intracellular proteins and enzymatic digestion of the lethally injured cell. The enzymes that digest the necrotic cell are derived from the lysosomes of the dying cells themselves and from the lysosomes of leukocytes that are called in as part of the inflammatory reaction.
Classification of necrosis:
1. Coagulative necrosis is a form of necrosis in which the architecture of dead tissues is preserved for a span of at least some days. Ischemia caused by obstruction in a vessel may lead to coagulative necrosis of the supplied tissue in all organs except the brain. A localized area of coagulative necrosis is called an infarct.
2. Liquefactive necrosis: in contrast to coagulative necrosis, is characterized by digestion of the dead cells, resulting in transformation of the tissue into a liquid viscous mass. It is seen in focal bacterial or occasionally fungul infections. The necrotic material is frequently creamy yellow because of the pressence of dead leukocytes and is called pus.
3. Gangrenous necrosis: is not a specific pattern of cell death but the term is commonly used in clinical practice. It is usually applied to a limb, generally the lower leg, that has undergone necrosis involving multiple tissue planes.
4. Caseous necrosis: is encountered most often infoci of tuberculous infection. The term caseous is derived from the febrile white appearance of the area of necrosis.
5. Fat necrosis: is a term that is entrenched in medical parlance but does not in reality denote a specific pattern of necrosis.
6. Fibrinoid necrosis: is a special form of necrosis usually seen in immune reactions involving blood vessels. This pattern of necrosis typically occurs when complexes of antigens and antibodies are deposited in the walls of arteries.
