The alveoli are small air sacs located at the end of the bronchial tree. The alveoli are where the critical gas exchange function of the lung occurs.

The walls of the alveoli are constructed of very special, very thin tissue. This tissue permits oxygen to pass from the air inside the lung into the blood that the heart pumps through the lung. At the same time oxygen moves across the alveoli into the blood, carbon dioxide (a gas the body generates as a waste product) passes from the blood into the alveoli. The carbon dioxide is expelled from your body when you exhale.

This photograph illustrates the location of the alveoli within the respiratory system.

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One type of damage that asbestos causes in the lungs is scarring. Scarring in the lung caused by asbestos exposure produces a disease called asbestosis.

Asbestos injures the tissue of the alveoli. The injured lung tissue is replaced by the body's all-purpose repair material -- scar tissue. The scar tissue that forms in the lung in response to asbestos injury is the same tissue that forms after a cut or a surgical incision heals.

Scar tissue does not function as normal lung tissue. It becomes very difficult for the alveoli to continue to exchange gas. When enough scar tissue forms in the lung from asbestos injury, the alveoli cannot move sufficient oxygen into the blood and the person becomes short of breath.

In severe cases, supplemental oxygen is required for the person to breathe. It becomes increasingly difficult to do simple things, like tie your shoes. In some cases, oxygen starvation is so severe, it is difficult for the person to eat.

This photograph illustrates scar tissue around the alveoli.

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