Student Memory Support
Cellular Injury: Causes, Mechanisms and Subcellular Responses
3rd Year MBBS • Foundation Module • High-yield rapid revision and memory reinforcement
1. High-Yield Flashcards
Tap each question to reveal the answer.
What is etiology in pathology?
The underlying cause of a disease.
What does pathogenesis describe?
The sequence of events through which a cause produces disease.
What is the earliest major consequence of ATP depletion in an injured cell?
Failure of ATP-dependent ion pumps, leading to sodium and water accumulation and cellular swelling.
Why does hypoxic injury increase lactic acid inside the cell?
Reduced oxidative phosphorylation shifts metabolism toward anaerobic glycolysis.
Why is ischemia generally more damaging than isolated hypoxia?
It reduces oxygen and nutrient delivery and also impairs removal of metabolic waste.
What is the major mechanism of ischemia-reperfusion injury?
Additional injury caused by reactive oxygen species, calcium disturbance and inflammatory mechanisms after blood flow returns.
What are the three major cellular targets of reactive oxygen species?
Membrane lipids, proteins and DNA.
What is lipid peroxidation?
Free-radical damage to membrane lipids that reduces membrane stability and function.
What two changes strongly indicate irreversible cell injury?
Persistent mitochondrial dysfunction and severe membrane damage.
What is heterophagy?
Lysosomal digestion of material that originated outside the cell.
What is autophagy?
Lysosomal degradation and recycling of the cell’s own damaged or unnecessary components.
How do phagocytosis and pinocytosis differ?
Phagocytosis takes up large particles; pinocytosis takes up extracellular fluid and dissolved substances.
What is enterohepatic circulation?
Recycling of a substance from liver to bile to intestine, followed by reabsorption into portal blood and return to the liver.
What is the clinical significance of enterohepatic circulation?
It can delay elimination and prolong persistence of some substances or drugs in the body.
2. Mnemonics
Mnemonic Title: Major Causes of Cell Injury
“O PIC GIN”
Meaning: Oxygen deprivation, Physical agents, Infectious agents, Chemicals/drugs, Genetic abnormalities, Immunological reactions, Nutritional abnormalities.
Mnemonic Title: Major Mechanisms of Cell Injury
“A-CROM”
Meaning: ATP depletion, Calcium imbalance, Reactive oxygen species, Organelle/mitochondrial damage, Membrane damage.
Mnemonic Title: Major Reactive Oxygen Species Targets
“LiP-DNA”
Meaning: Lipids, Proteins and DNA are major targets of oxidative injury.
3. Memory Tables
Reversible vs Irreversible Cell Injury
| Feature | Reversible Injury | Irreversible Injury |
|---|---|---|
| Recovery | Possible | Not possible |
| Morphology | Cell swelling, blebs | Severe membrane breakdown |
| Mitochondria | Function potentially recoverable | Persistent dysfunction |
| Membrane integrity | Largely preserved | Severely compromised |
| Outcome | Return toward normal | Cell death |
Phagocytosis, Pinocytosis, Heterophagy and Autophagy
| Process | Material | Key Function |
|---|---|---|
| Phagocytosis | Large extracellular particles | Cellular uptake |
| Pinocytosis | Extracellular fluid and solutes | Fluid-phase uptake |
| Heterophagy | Externally derived material | Lysosomal digestion |
| Autophagy | Own damaged components | Degradation and recycling |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Etiology = cause; pathogenesis = mechanism and sequence; morphology = structural change.
- Cell injury begins when stress exceeds the cell’s capacity to maintain homeostasis.
- The nature, severity and duration of injury determine whether damage remains reversible.
- ATP depletion causes membrane pump failure and cellular swelling.
- Anaerobic glycolysis increases lactic acid and lowers intracellular pH.
- Ischemia compromises oxygen, nutrients and waste removal; hypoxia primarily reduces oxygen availability.
- Reactive oxygen species damage lipids, proteins and DNA.
- Persistent mitochondrial dysfunction plus severe membrane damage indicates irreversible injury.
- Autophagy handles intracellular material; heterophagy handles externally derived material.
- Enterohepatic circulation may prolong persistence of some drugs or other substances.
Common KMU Trap:
Phagocytosis is the uptake of large particles, whereas heterophagy is the lysosomal digestion of externally derived material after uptake.
5. Clinical Memory Hooks
Temporary coronary obstruction → ATP depletion → pump failure → myocardial cellular swelling
Restoration of blood flow after ischemia → reactive oxygen species → additional reperfusion injury
Damaged mitochondrion inside a stressed cell → lysosomal degradation → autophagy
Drug secreted in bile and reabsorbed from intestine → enterohepatic circulation → prolonged persistence
6. Starred High-Yield Exam Points
- ⭐ ATP depletion → Na⁺/K⁺ pump failure → intracellular sodium and water accumulation → cellular swelling.
- ⭐ Ischemia is generally more damaging than isolated hypoxia because substrate delivery and waste removal are also impaired.
- ⭐ Reactive oxygen species cause lipid peroxidation, protein modification and DNA damage.
- ⭐ Reversible injury is characterized by recoverable dysfunction with cellular and organelle swelling.
- ⭐ Persistent mitochondrial dysfunction and severe membrane damage are key markers of irreversible injury.
- ⭐ Heterophagy digests externally derived material; autophagy degrades the cell’s own damaged components.
- ⭐ Enterohepatic circulation: liver → bile → intestine → reabsorption → portal blood → liver.