Reversible cell injury, types of degeneration and its organ manifestation

1. Reversible Cell Injury

• Early, mild injury → functional/morphological changes reverse if stimulus removed; no membrane damage or nuclear dissolution yet.
• Persistent/severe injury → “point of no return” → irreversible injury.
• Markers of irreversibility:
  1. Loss of membrane function/integrity
  2. Ca²⁺ influx → autolytic enzyme activation
  3. Irreversible mitochondrial dysfunction
• Sequence: reversible (cell swelling) → irreversible without signs → irreversible with signs (irreversibility precedes visible signs).

2. Types of Degeneration

Cellular swelling / hydropic (vacuolar) degeneration

• ↓ATP → failure of ion pumps → Na⁺/H₂O influx → swelling; organ pale and heavier.
• Cytoplasmic vacuoles = pinched-off ER segments. Earliest manifestation of injury.

Fatty degeneration (steatosis)

• Abnormal triglyceride accumulation in cells of fat metabolism: hepatocytes, myocardium, kidney.
• Morphology: diffuse (toxic) vs spotty (hypoxic); fat vacuoles push nucleus to periphery; stains: Oil-red O, Sudan black.
• Causes: alcohol (↓NAD → ↓fatty-acid oxidation), hypoxia, protein malnutrition (↓apoprotein → ↓lipoprotein export), diabetes/obesity (excess fat).

3. Organ Examples

Hepatic steatosis (fatty liver)

• Alcoholic liver disease: chronic intake → ↓fat catabolism/lipoprotein synthesis; sequence steatosis → hepatitis → cirrhosis.
• NAFLD: type 2 DM/obesity; insulin resistance → impaired FA oxidation, ↑FA uptake, ↓VLDL. Fat only = NAFLD; fat + inflammation/damage = NASH.
• Morphology: enlarged (4–6 kg), soft, yellow liver, tense capsule (reversible) → fibrosis around central veins → cirrhosis.

Nutmeg liver

• Right-sided heart failure → venous congestion → centrilobular hepatocytes deoxygenated + fatty, periportal cells spared → nutmeg pattern.

Cardiac fatty change

• Tiger heart (degeneratio adiposa insularis): yellow-brown subendocardial stripes from prolonged hypoxia (anemia, pulmonary disease); reversible.
• Diffuse fatty change: toxic (diphtheria toxin, adriamycin/chemotherapy).

💡 High-yield: Cellular (hydropic) swelling is the earliest reversible change; fat vacuoles displacing the nucleus = steatosis. Ca²⁺ influx + membrane/mitochondrial failure mark the irreversible “point of no return.” Nutmeg liver = right heart failure congestion.