MORPHOLOGICAL PATTERNS OF NECROSIS

Necrosis

• Necrosis refers to a spectrum of morphologic changes that occur in cells following cell death in living tissue.

• Necrosis occurs only in living organisms.

• Necrosis is distinct from physiological cell death (apoptosis).

• Necrosis is the sum of two processes that follow cell death in living tissues or organs:

  • Denaturation of proteins.

  • Enzymatic digestion of organelles.

• Necrosis is the point of no return.

Classification of Necrosis

• Coagulative necrosis

• Liquefactive necrosis

• Gangrenous necrosis

• Caseous necrosis

• Enzymatic fat necrosis

Apoptosis

• Causes of apoptosis:

  • Embryogenesis

  • Hormone-dependent involution in the adult

  • Cell deletion in populations of cells which have normal “turnover”

• Morphological pattern of death by apoptosis:

  • Cell shrinkage

  • Chromatin condensation

  • Apoptotic bodies

  • Phagocytosis of apoptotic bodies by phagocytic cells

• Features of apoptosis:

  • Considered a natural event which plays an important role in the regulation of normal cell population density.

  • Apoptosis “looks” different than necrosis.

  • Apoptosis may play a role in the pathogenesis of neoplasms (next unit).

Heat Shock Proteins

• Proteins involved in adaptation to stressful/injurious stimuli

• Induced and constitutively synthesized

• Play an important role in normal cell metabolism

• Essential for cell survival in all species subjected to injury

• Induced during myocardial and cerebral ischemia

• Increased heat shock protein expression is correlated with attenuation of cell injury/death

• HSP 60 and HSP 70: chaperonins – involved in protein folding and targeting to the final destination

• Ubiquitin:

  • Facilitates degradation of proteins

Ubiquitin Activation

• Ubiquitin activation by linking enzymes.

• Free ubiquitin recycled.

• Damaged protein.

• Activated ubiquitin is linked to damaged protein.

• Ubiquitinated protein now recognized by protease.

• Abnormal protein is destroyed into amino acids.