Most common site of TB –
**Core Concept**
Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis, primarily affecting the lungs but also other parts of the body. The disease manifests in various forms, including pulmonary TB, which is the most common type.
**Why the Correct Answer is Right**
The most common site of TB is the lungs, specifically the apical and posterior segments of the upper lobes. This is due to the inhaled bacteria lodging in these areas, where the oxygen levels are lower, allowing the bacteria to survive and multiply. The lungs' rich blood supply and lymphatic drainage also facilitate the spread of the infection to other parts of the body.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while the pleura, the membrane surrounding the lungs, can be affected by TB, it is not the most common site of the disease.
* **Option B:** This option is incorrect because TB can affect other parts of the body, such as the kidneys (renal TB) and spine (spinal TB), but these are not the most common sites.
* **Option C:** This option is incorrect because while TB can affect the brain (meningeal TB) and other organs, it is not the most common site of the disease.
**Clinical Pearl / High-Yield Fact**
TB can be spread through the air when an infected person coughs, sneezes, or talks, releasing droplets that contain the bacteria. This is why TB is often referred to as a "respiratory" disease.
**Correct Answer:** C. Lungs.