Lecture on Necrosis

Introduction to Necrosis

• Necrosis is one of the pathways for cell death.
• It occurs when a cell is irreversibly injured.
• Important distinction: Necrosis differs from the process of cutting or removing dead cells from the body.
• Necrosis is characterized by remaining a part of the living organism.

Definitions and Concepts

• Irreversible Cell Injury: Leads to cell death through necrosis or apoptosis.
  • Necrosis: Always pathological, involves accidental or unwanted injury.
  • Apoptosis: Can be physiological or pathological, a controlled process often beneficial to the organism (e.g., during embryogenesis).

Characteristics of Necrosis

• Necrosis is a series of morphological changes in lethally or irreversibly injured cells.
• Changes occur over several hours (4 to 12 hours) before they can be identified histologically.
• Involves changes in the cell, cytoplasm, nucleus, and organelles.
• The focus is on morphological changes rather than just cell injury.

Causes of Necrosis

• Severe trauma
• Severe ischemia
• Toxins
• Radiation

Biochemical Changes During Necrosis

• Energy Depletion: Inability to generate ATP due to halted metabolic pathways.
• Acidic Environment: Accumulation of lactic acid due to failure in energy metabolism, leading to protein denaturation.

Mechanisms of Necrosis

1. Protein Denaturation

   • Structural proteins (affect cell structure)
   • Functional proteins (enzymes, pumps, regulatory proteins)

2. Enzymatic Digestion

   • Autolysis: Destruction by the cell's own enzymes.
   • Heterolysis: Destruction by enzymes from inflammatory cells or microbes.

3. Disruption of Plasma Membrane

   • Leads to leakage of intracellular constituents.
   • Triggers inflammatory response in surrounding tissue.

Inflammation and Necrosis

• Necrosis typically involves a group of cells, leading to an inflammatory response.
• Inflammatory Reaction: Initiated by chemical substances from dead cells.
  • Vasodilation and increased permeability.
  • Infiltration by white blood cells to remove dead cells and promote tissue repair.
  • Distinct from apoptosis, which does not elicit inflammation.

Key Takeaways

• Necrosis is a series of morphological changes due to irreversible cell injury.
• Caused by protein denaturation, enzymatic digestion, and plasma membrane disruption.
• Results in an inflammatory response to clear dead tissue and begin repair.