Cell Injury - Types and Features

Cell Injury - 3

• Intended Learning Objectives: Recall cell death types, describe necrotic cell types, examples, and features, describe apoptotic cell morphology, and compare necrosis and apoptosis.

Types of Cell Death

• Necrosis: Local death of a group of cells within a living body. It's characterized by the breakdown (rupture) of cell membrane and enzymatic digestion of cellular contents.

• Apoptosis: Genetically controlled, programmed single cell death. Apoptosis is characterized by cell shrinkage, fragmentation of the nucleus, and formation of apoptotic bodies, which are later phagocytosed. There's no inflammation.

Necrosis

• Grossly: Necrotic area appears well-defined, swollen, opaque, pale yellow or pale red. Surrounded by a red inflammatory zone.

• Microscopically:

  • Cell membrane disappears. Cells become indistinct from each other.
  • Cytoplasm swells and coagulates, appearing homogenous and deeply eosinophilic.
  • Nucleus- characterized by pyknosis (shrunken and deeply basophilic), karyorrhexis (fragmented), and karyolysis (disappearance due to chromatin hydrolysis).

Types of Necrosis

• Coagulation Necrosis: Denaturation and coagulation of structural and enzymatic proteins. Cell outlines and tissue architecture are preserved. Examples: myocardial infarction due to coronary artery occlusion.

• Liquefactive Necrosis: Complete loss of cell and tissue structure due to liquefaction. Enzymes (autolysis or heterolysis) from cells or white blood cells break down the tissue. Examples: ischemic necrosis of brain (infarction), and pyogenic abscess (infection).

• Caseous Necrosis: Combination of coagulative and liquefactive necrosis. Tissue is firm grossly, but without cellular details microscopically. Example: Tuberculosis.

• Fat Necrosis: Necrosis of fat cells, caused by either trauma to fatty tissue or lipase enzyme action. Examples: Traumatic fat necrosis of the breast, Enzymatic fat necrosis of the pancreas and omentum in case of acute pancreatitis.

• Fibrinoid Necrosis: Death of cells in the inner layer of small blood vessels. It can lead to bleeding and internal damage throughout the body. Causes include malignant hypertension, autoimmune diseases (e.g., rheumatoid arthritis, lupus erythematosus), subacute bacterial endocarditis, and vasculitis (e.g., polyarteritis nodosa).

Apoptosis

• Morphologic Appearance:

  • Cell shrinkage
  • Deeply eosinophilic cytoplasm
  • Pyknotic (shrunken), then fragmented nucleus
  • Intact cell membrane (no rupture)
  • Formation of cytoplasmic buds
  • Each nuclear fragment goes with a cytoplasmic bud and breaks off to form apoptotic bodies.
  • Phagocytosis of apoptotic bodies by adjacent cells or macrophages
  • Absence of inflammatory response

• Physiological Examples:

  • Embryogenesis (development of lumens in hollow organs)
  • Hormone-dependent involution of tissues in adults (breast size changes after lactation, uterine involution after delivery).
  • Removal of self-reacting T lymphocytes in the thymus.

• Pathological Examples:

  • Councilman bodies in viral hepatitis (apoptotic hepatocytes)
  • Tumor cell death
  • Neuron loss in Alzheimer's disease
  • HIV-positive T-lymphocytes die by apoptosis.

Apoptosis vs. Necrosis

This quiz explores the different types of cell death, specifically necrosis and apoptosis. You will learn to recall the characteristics, examples, and morphological features associated with these processes. Compare and contrast necrotic cell types and apoptotic mechanisms for a deeper understanding of cellular responses to injury.