Diseases and ConditionsChronic Obstructive Pulmonary Diseases
(COPD) Emphysema is a lung disease that affects the walls of the
alveoli, the small sacs in the lungs that exchange oxygen for
carbon dioxide. Emphysema causes the alveolar walls to lose
their elasticity. This causes small pockets of dead air to
remain in the lungs and makes it difficult to exhale air from
the lungs. Most emphysema cases are caused by smoking, but about
3 percent of cases are caused by an inherited deficiency in a
protein that normally protects the alveoli. This protein is
alpha-1 antitrypsin (AAT). In emphysema caused by AAT
deficiency, the small airways that lead to the alveoli also
become damaged. In the normal lung, chemicals called proteases
are produced by the body's immune system to protect the lungs
from infection. Two types of proteases are elastase and trypsin.
If the concentration of proteases in the lungs is too great,
they can attack healthy lung tissue, destroying elastin, a
substance necessary to maintain the elastic