U01.04.002 Cell injury

Cell injury can be classified into reversible and irreversible injury based on the severity and duration of the insult. Understanding the mechanisms and morphological changes associated with each type is crucial for recognizing the progression from cell stress to cell death.

Reversible Cell Injury

Reversible cell injury occurs when cells are subjected to stress but can recover if the stress is removed. The following are key features:

Key Features:

Decreased ATP Production: This leads to reduced activity of Ca²⁺ and Na⁺/K⁺ pumps, causing cellular swelling (the earliest morphologic manifestation) and mitochondrial swelling.
Ribosomal/Polysomal Detachment: Results in decreased protein synthesis.
Plasma Membrane Changes: Includes blebbing of the plasma membrane.
Nuclear Changes: Chromatin clumping is observed.
Rapid Loss of Function: For instance, myocardial cells become noncontractile within 1-2 minutes of ischemia.
Myelin Figures: Aggregation of peroxidized lipids occurs, visible as myelin figures.

Points to Remember:

Reversible injury is characterized by cellular swelling and early functional loss but does not involve permanent structural damage.
Timely removal of the stressor can lead to full recovery.

Irreversible Cell Injury

Irreversible cell injury occurs when the damage is too severe for the cell to recover, ultimately leading to cell death. This can happen through necrosis or apoptosis.

Key Features:

Plasma Membrane Breakdown: Cytosolic enzymes (e.g., troponin) leak outside the cell, and Ca²⁺ influx activates degradative enzymes.
Mitochondrial Damage/Dysfunction: Loss of the electron transport chain leads to a significant decrease in ATP production.
Cytoplasmic Vacuolization: Often accompanies programmed cell death (apoptosis).
Lysosome Rupture: This leads to autolysis, where enzymes digest the cell from within.
Nuclear Degradation: Follows a sequence of pyknosis (nuclear condensation), karyorrhexis (nuclear fragmentation), and karyolysis (nuclear dissolution).
Amorphous Densities in Mitochondria: Represent severe mitochondrial injury, often associated with cell death.

Table: Reversible vs. Irreversible Cell Injury

Feature	Reversible Injury	Irreversible Injury
ATP Levels	Decreased, but recoverable	Significantly decreased, non-recoverable
Cell Swelling	Present	Severe and permanent
Mitochondrial Changes	Swelling	Severe dysfunction, loss of function
Plasma Membrane Integrity	Blebbing	Breakdown, leakage of enzymes
Nuclear Changes	Chromatin clumping	Pyknosis, karyorrhexis, karyolysis
Enzyme Leakage	None	Cytosolic enzymes leak into extracellular space
Cellular Function	Rapid loss but reversible	Permanent loss
Cytoplasmic Changes	Myelin figures (lipid accumulation)	Vacuolization, amorphous densities in mitochondria

Reversible vs. Irreversible Cell Injury

Points to Remember:

Irreversible injury is defined as the point of no return, where the structural and functional integrity of the cell is lost.
Key indicators of irreversible damage include nuclear degradation and mitochondrial dysfunction.

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U01.04.002 Cell injury

Reversible Cell Injury

Irreversible Cell Injury

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