Paper I
Question
Discuss the different causes of cell injury with examples.
Answer
Causes of cell injury
1. Hypoxia/Ischaemia
- Deprivation of oxygen supply — due to reduced blood flow (ischaemia), inadequate oxygenation (respiratory failure), or reduced oxygen-carrying capacity (anaemia, carbon monoxide poisoning)
- Example: myocardial infarction due to coronary artery occlusion
2. Physical agents
- Mechanical trauma, extremes of temperature, radiation, electric shock, sudden pressure changes
- Example: burns from thermal injury
3. Chemical agents and drugs
- Poisons, environmental pollutants, drug overdose/toxicity
- Example: cyanide poisoning (inhibits cytochrome oxidase, blocking oxidative phosphorylation), acetaminophen overdose (hepatotoxicity)
4. Infectious agents
- Bacteria, viruses, fungi, parasites — cause direct cytopathic injury or trigger host inflammatory/immune-mediated damage
- Example: viral hepatitis causing hepatocyte injury
5. Immunologic reactions
- Hypersensitivity reactions, autoimmune diseases
- Example: anaphylactic shock, autoimmune haemolytic anaemia
6. Genetic derangements
- Inherited enzyme deficiencies, chromosomal abnormalities
- Example: sickle cell disease (abnormal haemoglobin causing red cell injury)
7. Nutritional imbalances
- Deficiency states (protein-energy malnutrition, vitamin deficiencies) or excess (obesity, hypervitaminosis)
- Example: kwashiorkor, vitamin B12 deficiency causing megaloblastic changes
8. Ageing
- Cellular senescence with accumulated cellular and molecular damage over time, reducing the capacity of cells to respond to stress