Untitled Quiz

Cell Injury - 3

• Study objectives include recalling cell death types, describing necrotic cell types, examples, and morphological features, describing apoptotic cell morphology and types, and comparing necrotic and apoptotic cells.

Types of Cell Death

• Necrosis: Local death of a group of cells within the living body. It's a pathological process.
• Apoptosis: Genetically controlled, programmed, single cell death. Often a physiological process.

Necrosis

• Grossly: The necrotic area is well-defined, swollen, opaque, pale yellow or pale red, surrounded by a red zone of inflammatory hyperemia.
• Microscopically:
  • Cell membrane disappears, and cells become indistinct from each other.
  • Cytoplasm swells and coagulates, appearing homogenous and deeply eosinophilic.
  • Nucleus:
    • Pyknosis: the nucleus shrinks and becomes deeply basophilic.
    • Karyorrhexis: the nucleus fragments.
    • Karyolysis: the nucleus disappears due to chromatin hydrolysis.

Types of Necrosis

• Coagulative necrosis: Denaturation and coagulation of structural and enzymatic proteins. Preserves cell outlines and tissue architecture. Examples include myocardial infarction due to coronary artery occlusion.
• Liquefactive necrosis: Necrosis with complete loss of cell and tissue structure due to liquefaction by hydrolytic enzymes. Examples are ischemic necrosis of brain (infarction) and pyogenic abscess.
• Caseous necrosis: A combination of coagulative and liquefactive necrosis. The tissue is firm (grossly) and lacks cellular details or tissue outline (microscopically). An example is tuberculosis.
• Fat necrosis: Necrosis of fat cells, either from trauma to fatty tissue or the action of lipase enzyme, Often results in whitish yellow nodules. Examples include traumatic fat necrosis of the breast and enzymatic fat necrosis of the pancreas and omentum in case of pancreatitis.
• Fibrinoid necrosis: Death of cells in the inner layer of small blood vessels. Can lead to bleeding and internal damage throughout the body. Causes can include malignant hypertension, autoimmune diseases (like rheumatoid arthritis and systemic lupus erythematosus), subacute bacterial endocarditis, and vasculitis (like polyarteritis nodosa)..

Apoptosis

• Morphologic appearance:
  • Cell shrinkage
  • Deeply eosinophilic cytoplasm
  • Pyknotic nucleus, then fragmentation
  • Intact cell membrane
  • Formation of cytoplasmic buds
  • Each nuclear fragment forms with a cytoplasmic bud and breaks off to form apoptotic bodies,
  • Phagocytosis of apoptotic bodies by adjacent cells or macrophages.
  • Lack of inflammatory response
• Physiological examples:
  • Embryogenesis (development of lumens)
  • Hormone-dependent involution in adults (e.g., breast size change after lactation, uterine involution after delivery)
  • Removal of self-reacting T-lymphocytes in the thymus
• Pathological examples:
  • Councilman bodies (apoptotic hepatocytes in viral hepatitis)
  • Tumor cell death
  • Neurons lost in Alzheimer's disease
  • HIV-positive T-lymphocytes

Apoptosis vs. Necrosis