Pathophysiology
Clinical meaning
Tuberculosis is caused by Mycobacterium tuberculosis, an acid-fast bacillus transmitted through airborne droplet nuclei. When inhaled, the bacteria reach the alveoli where macrophages attempt to contain them, forming granulomas (tubercles). In most people (90-95%), the immune system contains the infection in a latent state. Reactivation occurs when immunity weakens, allowing bacteria to multiply and cause active disease with cavitary lesions typically in the upper lobes.