Lecture on Necrosis

Introduction to Necrosis

• Necrosis: A pathway for cell death due to irreversible injury.
• Difference between necrosis and apoptosis:
  • Both result from irreversible cell injury.
  • Apoptosis can be physiological or pathological.
  • Necrosis is always pathological.

Characteristics of Necrosis

• Definition: Necrosis is a series of morphological changes in a lethally injured cell.
• Occurs when a cell cannot adapt, recover, or reverse its severe/prolonged injury.
• Histological changes take 4 to 12 hours to be identified under a light microscope.
• Necrotic changes include alterations in the cell's cytoplasm, nucleus, and organelles.

Causes and Processes of Necrosis

• Triggered by:
  • Trauma
  • Severe ischemia
  • Toxins
  • Radiation
• Cell Death Pathways:
  • Necrosis vs. Apoptosis
  • Necrosis involves plasma membrane disruption and leakage of intracellular materials.
  • Can lead to inflammation due to injury to surrounding tissues.

Biochemical Changes in Necrosis

• Energy Depletion: Loss of ATP leads to conversion of glucose to lactic acid, making the cell environment acidic.
• Protein Denaturation:
  • Structural and functional proteins (enzymes) undergo denaturation.
  • Leads to morphological changes including loss of structural integrity.

Morphological Changes

• Cytoplasmic Changes:
  • Increase in eosinophilia (more pinkish appearance) due to protein denaturation and ribosome disintegration.
  • Loss of glycogen granules makes cytoplasm appear glassy and homogeneous.
  • Moth-eaten appearance due to disappearance of organelles.
  • Formation of myelin figures (crumpled cell membranes).
• Nuclear Changes:
  • Karyolysis: Gradual fading away of the nucleus.
  • Pyknosis: Condensation and shrinking of the nucleus.
  • Karyorrhexis: Fragmentation of the nucleus.

Types of Necrosis

• Coagulative Necrosis:
  • Occurs in myocardial infarction and severe ischemia.
  • Cell structure preserved initially due to denatured enzymes.
  • Characterized by a lack of enzymatic digestion early on.
  • Repair involves inflammatory cells (neutrophils, macrophages) and fibrosis.
• Liquefactive Necrosis:
  • Occurs in the brain, abscesses, and with pyogenic infections.
  • Enzymatic digestion is intense, leading to tissue liquification.
  • Results in pus formation, containing live, dead, and dying cells.
  • Abscess: Localized pus pocket, surrounded by active neutrophils and fibroblasts trying to wall off the infection.

Special Considerations

• Central Nervous System:
  • Unique in undergoing liquefactive necrosis instead of coagulative, possibly due to less structural protein or different enzyme dynamics.
• Inflammation:
  • Necrosis induces inflammation, unlike apoptosis.
  • Inflammation aids in removing dead tissue and initiating repair.

Conclusion

• Necrosis is a complex process involving structural and enzymatic changes leading to cell death.
• Understanding necrosis helps in diagnosing tissue damage and formulating treatment strategies.

Key Takeaways

• Necrosis involves morphological and biochemical changes.
• Different types of necrosis occur depending on the tissue and nature of injury.
• Necrosis triggers inflammatory responses, unlike apoptosis.