Pathology
Cell Injury and Adaptation
Cell injury and adaptation for MBBS and NEET-PG: reversible versus irreversible injury, patterns of necrosis, apoptosis, pathological calcification and cellular adaptations, mapped to NMC codes.
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Cell Injury and Adaptation
Cell injury and adaptation for MBBS and NEET-PG: reversible versus irreversible injury, patterns of necrosis, apoptosis, pathological calcification and cellular adaptations, mapped to NMC codes.
This chapter explains how cells respond to stress, from adaptation through reversible injury to death. It covers the mechanisms of cell injury, the intracellular accumulations, the patterns of necrosis and apoptosis, pathological calcification and gangrene, and the adaptive responses of atrophy, hypertrophy, hyperplasia, metaplasia and dysplasia.
High-yield: Cell Injury and Adaptation
- Reversible cell injury shows cellular swelling and fatty change; irreversible injury shows severe mitochondrial damage and membrane rupture.
- Hypoxia acting through ATP depletion is the most common cause of cell injury.
- Loss of ATP causes failure of the sodium-potassium pump, leading to cellular swelling, the earliest morphological change.
- Influx of calcium and increased cytosolic calcium activate enzymes that damage membranes, proteins and DNA.
- The two hallmarks of irreversibility are severe membrane damage and profound mitochondrial dysfunction.
- Coagulative necrosis preserves tissue architecture and is typical of ischaemic infarcts in all organs except the brain.
- Liquefactive necrosis is seen in brain infarcts and in bacterial abscesses.
- Caseous necrosis, a cheesy amorphous debris, is characteristic of tuberculosis.
- Fat necrosis is seen in acute pancreatitis, where lipase releases fatty acids that form calcium soaps (saponification).
- Fibrinoid necrosis is seen in immune vascular injury such as malignant hypertension and polyarteritis nodosa.
- Apoptosis is programmed single-cell death with cell shrinkage, nuclear fragmentation and apoptotic bodies, without inflammation.
- Necrosis affects sheets of cells, causes membrane rupture and provokes inflammation; apoptosis does not.
- Dystrophic calcification occurs in damaged or dead tissue with normal serum calcium; metastatic calcification occurs in normal tissue with hypercalcaemia.
- Metaplasia is a reversible change of one mature cell type to another, such as squamous metaplasia in the bronchus of smokers.
- Dysplasia is disordered growth with atypia and is a pre-malignant change, unlike the benign adaptations of hyperplasia and metaplasia.
Patterns of necrosis
- **Coagulative:** Ischaemic infarcts of solid organs; architecture preserved. Not the brain.
- **Liquefactive:** Brain infarcts and bacterial abscesses; tissue digested to fluid.
- **Caseous:** Tuberculosis; cheesy amorphous debris within granulomas.
- **Fat / Fibrinoid:** Acute pancreatitis (saponification); immune vascular injury (malignant hypertension).
NMC competencies in this chapter
- **PA2.1:** Causes, mechanisms, types and effects of cell injury and their clinical significance
- **PA2.2:** Reversible versus irreversible injury: mechanisms and morphology
- **PA2.3:** Intracellular accumulations of fats, proteins, carbohydrates and pigments
- **PA2.4:** Cell death: necrosis and apoptosis
- **PA2.5:** Pathological calcification and gangrene
- **PA2.6:** Cellular adaptations: atrophy, hypertrophy, hyperplasia, metaplasia, dysplasia
- **PA2.7:** Mechanisms of cellular ageing and apoptosis
- **PA2.8:** Identify forms of cell injury in gross and microscopic specimens
Frequently Asked Questions
What is the earliest sign of reversible cell injury?
Cellular swelling, caused by failure of the ATP-dependent sodium-potassium pump, which allows sodium and water to accumulate inside the cell.
How does apoptosis differ from necrosis?
Apoptosis is programmed death of single cells with shrinkage and no inflammation, while necrosis affects groups of cells, ruptures membranes and provokes inflammation.
What type of necrosis is seen in tuberculosis?
Caseous necrosis, a soft cheesy area of amorphous debris seen within granulomas, is the hallmark of tuberculosis.
What is the difference between dystrophic and metastatic calcification?
Dystrophic calcification occurs in dead or damaged tissue with normal serum calcium, while metastatic calcification occurs in normal tissue when serum calcium is raised.
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