Cellular Injury: Reversible vs Irreversible

Understanding the mechanisms and consequences of cellular damage

General Pathology

Introduction to Cellular Injury

Key Concept: Watch this video to understand the fundamental concepts of cellular Injury before diving into the interactive lessons.

Introduction to Cellular Injury

Cells constantly face various stressors that can lead to injury. Understanding the difference between reversible and irreversible injury is crucial in pathology, as it determines whether cells can recover or are destined to die.

Key Concept:

Reversible cellular injury represents an early stage of damage where cells can recover if the stressor is removed. In this state, cellular damage is present but can be repaired if the stressor is removed in time.

Reversible Cellular Injury

Morphological Changes

  • Plasma membrane blebs
  • Mitochondrial swelling
  • Dilated endoplasmic reticulum
  • Overall cellular swelling
  • Clumping of nuclear chromatin

Biochemical Changes

  • Decreased ATP production
  • Reduced protein synthesis
  • Detachment of ribosomes from ER
  • Activation of autophagy
  • Maintained membrane integrity

Common Patterns

Hydropic Change

Cellular swelling due to sodium-potassium pump failure, causing water influx and giving cells a pale, swollen appearance.

Fatty Change

Triglycerides accumulate in the cytoplasm, particularly in liver and heart cells that process large amounts of fat.

Causes of Reversible Injury:

Hypoxia (reduced oxygen delivery)
Chemical toxins
Infections
Nutritional imbalances

Irreversible Cellular Injury

Irreversible cellular injury occurs when damage exceeds the cell's repair capacity, leading to cell death. These changes cannot be reversed even if the original injurious stimulus is removed.

Two Major Mechanisms of Cell Death

Necrosis

  • Results from pathological injury
  • Cell swelling and membrane rupture
  • Release of cellular contents
  • Triggers inflammatory response
  • Nuclear changes: pycnosis, karyorexis, karyolysis

Apoptosis

  • Programmed cell death (physiological)
  • Cell shrinkage and chromatin condensation
  • Membrane blebbing and apoptotic bodies
  • Phagocytosed without inflammation
  • Controlled, energy-dependent process

Transition to Irreversible Injury:

Critical Events

  • Massive calcium influx
  • Profound ATP depletion
  • Extensive membrane damage
  • Lysosomal rupture

Consequences

  • Enzyme activation degrading membranes
  • Energy production collapse
  • Point of no return reached
  • Cell death becomes inevitable