Tuberculosis most commonly involves which organ?

• A. Heart
• B. Lungs
• C. Liver
• D. Brain

Answer: (B)

Tuberculosis is acquired by inhaling airborne droplets, so the first place the bacteria encounter and multiply is the lungs. The alveoli provide the initial site for Mycobacterium tuberculosis to settle, and the pulmonary environment becomes the primary battlefield where the infection is established. That's why the lungs are the most commonly involved organ in TB—the bacilli are delivered directly to and replicate in the lung tissue, and the characteristic granulomatous response begins there with a primary complex in the lungs and nearby lymph nodes.

Extrapulmonary TB can occur, especially in immunocompromised individuals, and the infection can spread to places like lymph nodes, spine, brain, liver, or kidneys, but those sites are less commonly affected than the lungs. In reactivation TB, the upper lobes are often involved due to higher oxygen tension, but the lung remains the most frequent organ affected overall.