Lecture I

• Cell injury is reversible up to a point, but if the injurious stimulus is persistent or severe, the cell suffers irreversible injury and ultimately undergoes cell death
• Causes of cell injury include:

  • Oxygen Deprivation: reduction of aerobic oxidative respiration
  • Physical Agents: mechanical trauma, extremes of temperature (burns and deep cold), sudden changes in atmospheric pressure, radiation, and electric shock
  • Chemical Agents and Drugs
  • Infectious Agents
  • Immunologic Reactions
  • Genetic Abnormalities
  • Nutritional Imbalances
• Progression of Cell Injury and Death:

  • Reversible Cell Injury:
  • Early stage: characterized by reversible cellular swelling (e.g., hydropic degeneration)
  • Late stage: characterized by irreversible membrane damage and cell death
• Adaptations of Cellular Growth and Differentiation:

  • Changes experienced by cells in response to physiological or pathological stimuli
  • Persistent stress can lead to cell injury
• Hypertrophy:

  • Increase in the size of cells that increases the size of the affected organ
  • Mechanisms of Hypertrophy:
  • Result of increased cellular protein production
  • Activation of signaling pathways and production of growth factors
• Hyperplasia:

  • Increase in the number of cells in an organ or tissue in response to a stimulus
  • Mechanisms of Hyperplasia:
  • Result of growth factor-driven proliferation of mature cells and, in some cases, increased output of new cells from tissue stem cells
• Atrophy:

  • Reduction in the size of an organ or tissue due to a decrease in cell size and number
  • Mechanisms of Atrophy:
  • Results from decreased protein synthesis and increased protein degradation in cells
• Metaplasia:

  • Reversible change in which one differentiated cell type is replaced by another cell type
  • Metaplasia does not result from a change in the phenotype of an already differentiated cell type; it results from either the reprogramming of local tissue stem cells or colonization by differentiated cell populations from adjacent sites