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Comprehensive Basic Science Flashcards

7 cards from real NBME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A patient develops a granulomatous reaction with caseous necrosis on biopsy. Which organism is most likely responsible?

    Answer: Mycobacterium tuberculosis

    Mycobacterium tuberculosis classically causes caseating granulomas mediated by T-cell hypersensitivity (Type IV) with central cheese-like necrosis.

  2. A surgical specimen shows coagulative necrosis. Which organ is most commonly associated with this pattern after ischemic infarction?

    Answer: Heart

    Coagulative necrosis preserves tissue architecture because ischemia denatures both structural and enzymatic proteins, and is classic in the heart, kidney, and spleen.

  3. A gram-positive rod forming spores in soil causes a wound infection with gas formation and tissue crepitus. Which organism is responsible?

    Answer: Clostridium perfringens

    Clostridium perfringens produces alpha toxin (lecithinase) causing gas gangrene, with gas formation from fermentation in anaerobic tissue.

  4. A patient develops hemolytic anemia when given primaquine. Heinz body formation is noted. Which enzyme is deficient?

    Answer: Glucose-6-phosphate dehydrogenase

    G6PD deficiency reduces NADPH and glutathione, impairing oxidative stress defense and causing Heinz body formation from denatured hemoglobin.

  5. A biopsy specimen shows Russell bodies within plasma cells. Which condition best explains this finding?

    Answer: Multiple myeloma

    Russell bodies are intracytoplasmic immunoglobulin-filled inclusions seen in neoplastic plasma cells, characteristic of multiple myeloma.

  6. A patient with a right middle cerebral artery infarct develops contralateral weakness. The stroke core shows liquefactive necrosis. Why does brain infarction produce liquefaction rather than coagulation?

    Answer: High lipid content and abundant lysosomal enzymes from activated microglia liquefy tissue

    The brain's high lipid content and microglial enzymatic digestion promote liquefactive necrosis rather than the protein-preserving coagulative pattern seen in other organs.

  7. A urease-positive, gram-negative rod colonizes the gastric mucosa. Disruption of which defense mechanism is most critical to its survival?

    Answer: Mucus-bicarbonate barrier

    H. pylori uses urease to generate ammonia, neutralizing local acid and allowing it to penetrate and disrupt the protective mucus-bicarbonate layer.