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Causes
By Mayo Clinic staff
When you inhale, air travels through your nose or mouth, down your throat, through your larynx to your trachea — the main passageway for air to your lungs. Your trachea splits into two branches called bronchi, one carrying air to the left lung, one to the right. Within each lung, the bronchi branch off over a dozen times into smaller and smaller airways. Some of the smallest of these airways (bronchioles) lead into tiny ducts (alveolar ducts) that end in microscopic air sacs (alveoli).
Alveoli have very thin, elastic walls that allow an exchange of gases vital to your health — oxygen flows from the alveoli into your bloodstream to nourish your body, and carbon dioxide flows from your bloodstream into the alveoli and on into your bronchi, to be expelled.
A natural screening system
Normally, microorganisms, dust and other foreign particles in the air you breathe are removed by microscopic hairs on the surface of your airways that beat hundreds of times a minute (cilia). The cilia sweep the particles into your upper airway, where the particles are swallowed into your digestive system, trapped in your nose hairs or expelled when you cough.
Even when unwanted particles do get into your lungs, immune cells destroy most of them. Alveoli, for example, house their own special cleanup crew — immune cells called macrophages, which are attracted to and ingest foreign substances, such as smoke particles, dust and chemicals.
Fibers resist breakdown
Unfortunately, asbestos fibers are difficult to destroy, even for macrophages. When a macrophage attempts to ingest an asbestos fiber, it often fails because the fiber is too long and partially resistant to breakdown. In the process, however, the macrophage leaks out substances that were supposed to destroy the foreign body, but these substances can also harm the alveoli. This causes the alveoli to become inflamed and eventually scar, a process referred to as fibrosis.
If many fibers are inhaled over a long period, the cumulative scarring of alveoli reduces their ability to exchange oxygen and carbon dioxide. The result is that your lung capacity diminishes, oxygen exchange is diminished, and you feel increasingly short of breath. Also, because the lungs are stiff, like a dried sponge, it takes a great deal of muscular effort to breathe.
For unknown reasons, not everyone exposed to asbestos for long periods develops asbestosis. Genetic factors may play a role.
- O'Reilly KM. Asbestos-related lung disease. American Family Physician. 2007;75:683.
- Cowie, RL, et al. Asbestos-related fibrosis of the lungs (asbestosis). In:
- Mason, RJ, et al. Murray & Nadel's Textbook of Respiratory Medicine 4th ed. St. Louis, Mo.: W.B. Saunders; 2005:1748.
- Asbestos-related disorders. The Merck Manuals Online Medical Library: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/sec05/ch057/ch057c.html. Accessed Nov. 16, 2008.
- Asbestos exposure: Questions and answers. National Cancer Institute. http://www.cancer.gov/cancertopics/factsheet/Risk/asbestos. Accessed Nov. 16, 2008.
- What are the risk factors for malignant mesothelioma? American Cancer Society. http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_for_malignant_mesothelioma_29.asp. Accessed Nov. 16, 2008.
- Asbestos exposure. Family Practice Notebook. http://www.fpnotebook.com/Lung/Asbestos/AsbstsExpsr.htm. Accessed Nov. 16, 2008.
- Asbestos: General information. Agency for Toxic Substances & Disease Registry. http://www.atsdr.cdc.gov/asbestos/asbestos/health_effects/index.html. Accessed Nov. 16, 2008.
- Rosenow EC (expert opinion). Mayo Clinic, Rochester, Minn. Nov. 23, 2008.
