Necrosis


Biology Presentation

 By: Ingrid Hidalgo & Julio Lezcano

 

 

 

 

Is the name given to accidental death of cells and living tissue. Necrosis is less orderly than apoptosis, which is part of programmed cell death. In contrast with apoptosis, cleanup of cell debris by phagocytes of the immune system is generally more difficult, as the disorderly death generally does not send cell signals which tell nearby phagocytes to engulf the dying cell. This lack of signalling makes it harder for the immune system to locate and recycle dead cells which have died through necrosis than if the cell had undergone apoptosis. The release of intracellular content after cellular membrane damage is the cause of inflammation in necrosis.

Causes...

There are many causes of necrosis including prolonged exposure to injury, infection, cancer, infarction, poisons, bites from some spiders such as brown recluses and inflammation. Severe damage to one essential system in the cell leads to secondary damage to other systems, a so-called "cascade of effects". Necrosis can arise from lack of proper care to a wound site. Necrosis is accompanied by the release of special enzymes, that are stored by lysosomes, which are capable of digesting cell components or the entire cell itself. The injuries received by the cell may compromise the lysosome membrane, or may initiate an unorganized chain reaction which causes the release in enzymes.

 

Morphologic patterns

There are seven distinctive morphologic patterns of necrosis:

  • Coagulative necrosis is typically seen in hypoxic environments (e.g. myocardial infarction, infarct of the spleen). Cell outlines remain after cell death and can be observed by light microscopy.
  • Liquefactive necrosis is usually associated with cellular destruction and pus formation (e.g. pneumonia). This is typical of bacterial or, sometimes, fungal infections because of their ability to stimulate an inflamatory reaction. Curiously, ischemia (restriction of blood supply) in the brain produces liquefactive rather than coagulative necrosis.
  • Gummatous necrosis is restricted to necrosis involving spirochaetal infections.
  • Haemorrhagic necrosis is due to blockage of the venous drainage of an organ or tissue (e.g. in testicular torsion).
  • Caseous necrosis is a specific form of coagulation necrosis typically caused by mycobacteria (e.g. tuberculosis).
  • Fatty necrosis results from the action of lipases on fatty tissues (e.g. acute pancreatitis, breast tissue necrosis).
  • Fibrinoid necrosis is caused by immune-mediated vascular damage. It is marked by deposition of fibrin-like proteinaceous material in arterial walls, which appears smudgy and eosinophilic on light microscopy.