Pathology Cheat Sheet
Crossing the Threshold
Cell injury for NEET-PG exams: hypoxia vs ischaemia, ATP depletion, calcium influx, free radicals, reperfusion injury, and reversible vs irreversible change.
MedNext Academy | 3 min read
Crossing the Threshold
Cell injury for NEET-PG exams: hypoxia vs ischaemia, ATP depletion, calcium influx, free radicals, reperfusion injury, and reversible vs irreversible change.
The causes of cell injury and the biochemical mechanisms that decide whether an injured cell recovers or dies.
High-yield lines
- Hypoxia reduces oxidative phosphorylation, while ischaemia adds loss of substrate delivery and waste removal, making ischaemia more damaging.
- The earliest change of reversible cell injury on light microscopy is cellular swelling due to failure of the Na-K-ATPase pump.
- The earliest ultrastructural change of cell injury is mitochondrial swelling with clearing of the intermembranous space.
- The six interconnected mechanisms of injury are ATP depletion, mitochondrial damage, calcium influx, reactive oxygen species, membrane damage, and DNA or protein damage.
- Rising cytosolic calcium activates phospholipases, proteases, endonucleases, and ATPases that damage the cell.
- The hydroxyl radical is the most reactive oxygen species and is generated from hydrogen peroxide by the iron-dependent Fenton reaction.
- Superoxide dismutase, catalase, and glutathione peroxidase form the main antioxidant defence system.
- The point of no return in cell injury is severe persistent mitochondrial dysfunction combined with plasma membrane damage.
- Neurons and cardiac myocytes are most vulnerable to ischaemia because they depend heavily on aerobic ATP production.
- Reperfusion injury is driven by a burst of reactive oxygen species, calcium overload, and inflammatory amplification when flow is restored.
- Enzyme leakage from ruptured membranes provides clinical markers such as troponin for cardiac injury and transaminases for hepatocyte injury.
- Membrane damage is the final common pathway that converts biochemical injury into visible necrosis.
Mapped competency codes
- PA2.1
- PA2.2
Continue into the full chapter
This summary maps to PA2-cell-injury-and-adaptation.
Frequently Asked Questions
What is the earliest change of reversible cell injury under light microscopy?
Cellular swelling (hydropic change), caused by failure of the sodium-potassium ATPase pump leading to water influx.
Why is ischaemia more harmful than pure hypoxia?
Ischaemia not only lowers oxygen but also stops glucose delivery for anaerobic glycolysis and prevents washout of lactate and toxic metabolites.
What defines the point of irreversibility in cell injury?
Severe and persistent mitochondrial dysfunction with cytochrome c release, together with irreparable plasma membrane damage.
How does reperfusion worsen tissue injury?
Restored oxygen triggers a reactive oxygen species burst, calcium overload floods ATP-depleted cells, and neutrophils and complement amplify inflammation.
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