Target Organ and System Toxicity
Why organs fail
Target organ toxicity reflects delivery, uptake, metabolic capacity, and repair. Liver: zone 3 (centrilobular) is rich in CYP enzymes and low in glutathione, so acetaminophen, carbon tetrachloride, and ethanol injure there; other agents produce zone 1 or bile duct injury. Kidney: the proximal tubule receives high blood flow and concentrates filtrate; aminoglycosides, cisplatin, heavy metals, and halogenated solvents target it. Lung: club (Clara) cells and pneumocytes are targets for paraquat, bleomycin, ozone, and 4-ipomeanol. CNS: the blood-brain barrier, lipophilicity, and the developing brain shape vulnerability. Heart: hERG blockade, anthracyclines, cocaine. Blood: marrow suppression, methemoglobinemia, hemolysis. Immune, reproductive, developmental, skin, and endocrine systems have distinctive mechanisms and windows of susceptibility.
Traps: the target organ is not necessarily the portal of entry; inhaled manganese affects the basal ganglia. Effects may be delayed (carcinogens, radiation) or appear only after re-challenge (sensitization). Species differences in metabolism and receptor biology limit extrapolation. Dose matters: therapeutic acetaminophen is safe, while overdose causes centrilobular necrosis through NAPQI formation and glutathione depletion.
Rule of thumb: map mechanism to anatomy. Metabolic activation plus antioxidant depletion predicts centrilobular hepatic injury; active tubular secretion and reabsorption predict proximal tubular nephrotoxicity; high lipophilicity plus barrier penetration predicts CNS effects.