Most disease processes have target organs; organs that are chiefly affected by the disease. Tuberculosis or TB (mycobacterium tuberculosis) is similar insofar as the target organ is the lungs but TB can also spread to other locations like bone tissue. It can also spread to other internal organs. In other words, when a person contracts TB, the first organ affected is usually the lungs (pulmonary system). Usually if TB is diagnosed early and treated properly, it can and often is, isolated in the lung tissue and does not spread to other structures and organs.
A good example of this is prostate cancer. When a male contracts prostate cancer, the prostate gland is affected but other organs and systems can be affected if the disease is not diagnosed early in the disease process. If left unchecked, prostate cancer rapidly spreads to other locations like the bladder, renal system, and large and small bowel.