Necrosis

 Necrosis is Series of morphological change in a lethaly injured Cell.

Necrosis is a pathologic process that is the consequence of severe injury.

Localised area of necrosis is called infarct.

Causes of necrosis :-

 • Loss of oxygen supply ( ischemia)

 • Exposure to microbial toxin

 • Burns and other forms of chemical and physical injury

 • Unusual situation in which active protease leak out of cell and damage surrounding tissue (as in pancreatitis)

Characteristics of necrosis :-

 • Denaturation of cellular protein

 • Leakage of cellular content through damage membrane

 • Local inflammation

 • Enzymatic digestion of lethal injured cell.

Necrosis - associated leakage of intracellular protein through damaged plasma membrane and ultimately into the circulation is the basis for blood test that detect tissue-specific cellular injury.

 • In myocardial infarction; cardiac specific troponins can be detected in blood as early as 2 hours after myocardial cell necrosis.

 • Bile duct epithelium expresses alkaline phosphatase

 • Hepatocyte expresses transaminases .

Necrotic cell as seen under light microscope :

 • Increased eosinophilia

 • Glassy homogeneous appearance

 • Moth eaten appearance

 • Precipitated by myelin figures

Necrotic cell as seen on the electron microscope:

 • Discontinues in plasma and organelles membrane

 • Dilation of mitochondria with the appearance of large amorphous densities

 • Intracytoplasmic myelin figure

 • Amorphous debris

 • Aggregation of fluffy material representing denatured proteins.

Nuclear changes follow one of the following pattern :-

 1. Karyolysis - complete dissolution of the chromatin due to enzymetic degradation by endonuclease

 2. Pyknosis - nuclear shrinkage, and increased basophila.

 3. Karyorrhexis - Nucleus get shrinkage and then undergoes fragmentation

Pattern of tissue necrosis (types of necrosis):-

 1. Coagulative necrosis

 • Architecture of Dead tissue is preserved for at least some days.

 • Injury denatures structural protein as well as enzyme , thus block the protolysis of the Dead cell.

 • As a result cell may persist for few days or weeks.

 • Ultimately cells get break down by the action of lysosomal enzyme drive from leukocytes, and also it removes the debris of dead cell by phagocytosis.

 • For example:- ischemia caused by obstruction in vessel may lead tissue to this necrosis except brain.

 2. Liquefactive necrosis

 • Digestion of the Dead Cell result in transformation of the tissue into viscous liquid.

 • It is seen in bacterial or fungal infection

 • Necrotic material Become yellow because of the presence of leukocytes called puss.

 • Example: hypoxic death of cell within central nervous system.

 3. Gangrenous necrosis

 • It does not follow specific pattern of cell death.

 • It generally occurs in lower leg that has lost its blood supply and has gone under necrosis.

 • When bacterial infection is caused, it goes more liquefactive necrosis. Because of the degradative enzymes in the bacteria and attracted leukocyte , give rise to so called wet gangrene.

 4. Caseous (cheese like) necrosis

 • It occurs in foci of tuberculosis infection.

 • White appearance of the area of necrosis. Known as granuloma .

 5. Fat necrosis

 • Fat destruction resulting from release of activated pancreatic lipase into the peritoneal cavity.

 • In this disorder, pancreatic enzymes licks out of damaged acinar cell and liquefying the membrane of fat cell in the peritoneum.

 • Visible chalky-white areas (fat saponification) is seen which helps to identify underlying disorder.

 6. Fibrinoid necrosis

 • Vascular damage usually seen in immune reaction involving blood vessel.

 • It occurs when complexes of antigen and antibodies are deposited in the Wall of arteries.

 • It result in a bright pink and amorphous appearance in H&E stains , called fibrinoid (fibrin like)

 • It is seen in immunologically mediated vasculitis syndrome.