Etiology of Cellular Injury: Causes and Mechanisms

Etiology of Cellular Injury

Cells may be injured through two primary pathways:

• Genetic causes: Discussed in the context of specific diseases.
• Acquired causes: Comprise the vast majority of common diseases afflicting mankind.

Based on the underlying agent, acquired causes of cell injury are categorized as follows:

1. Hypoxia and Ischemia

Cells require oxygen to generate energy and perform metabolic functions. Hypoxia is the most common cause of cell injury and may result from:

• Ischemia: Reduced blood supply to cells.
• Oxygen-carrying disorders: Anemia or carbon monoxide poisoning.
• Systemic issues: Heart or lung diseases.
• Increased tissue demand.

2. Physical Agents

• Mechanical trauma (e.g., road accidents)
• Thermal trauma (e.g., heat and cold)
• Electricity
• Radiation (e.g., ultraviolet and ionizing)
• Rapid changes in atmospheric pressure

3. Chemical Agents and Drugs

• Chemical poisons (e.g., cyanide, arsenic, mercury)
• Strong acids and alkalis
• Environmental pollutants
• Insecticides and pesticides
• High concentrations of oxygen
• Hypertonic glucose and salt
• Social agents (e.g., alcohol and narcotics)
• Therapeutic drug administration

4. Microbial Agents

Infections caused by bacteria, rickettsiae, viruses, fungi, protozoa, metazoa, and other parasites.

5. Immunologic Agents

While the immune system protects the host, it can cause injury through:

• Hypersensitivity reactions
• Anaphylactic reactions
• Autoimmune diseases

6. Nutritional Derangements

• Deficiency: Starvation, protein-calorie malnutrition (marasmus, kwashiorkor), mineral or trace element deficiencies.
• Excess: Obesity, atherosclerosis, heart disease, and hypertension.

7. Aging

Cellular senescence leads to an impaired ability to replicate and repair, ultimately culminating in cell death.

8. Psychogenic Diseases

9. Iatrogenic Factors

Diseases or deaths attributed to medical intervention, including errors in judgment or adverse effects of therapy (drugs, radiation).

10. Idiopathic Diseases

Diseases of unknown cause.