Pulmonary Q&A by Dr. Schiffman

Answer:

Bronchitis Slideshow Asthma Myths Quiz Slideshow

The lung has a variety of mechanisms that try to keep the lungs sterile. Sometimes small substances (grains of sand, dust, or certain organisms) get past these mechanisms and deposit in the lung tissue. The body's immune system responds to this deposition of foreign matter. In some cases, the substance can be destroyed with enzymes or cleared from the lung (sometimes by coughing); in other cases, the body walls off this foreign material into nodular densities that can calcify (meaning that there are small deposits of calcium-containing compounds), especially if any bleeding occurs. These are seen as calcified nodules on chest x-rays or CT scans. Organisms that can result in these nodules include tuberculosis, Rubella (the virus that causes German measles), and a variety of fungi.

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