In chronic obstructive pulmonary disease or COPD, the bronchioles and alveoli in the lungs become damaged, usually due to smoking. The bronchioles are small air passageways and the alveoli are tiny sacs where oxygen is transferred from the air into the bloodstream.

Other causes include:

• Occupational exposure to dust
• Asbestosis
• Silicosis
• Coal dust: black lung
• Occupational exposure to smoke
• Occupational exposure to fumes

Normally, the bronchioles and alveoli are open and elastic: they expand when air enters the lungs, and return to shape during air exits the lungs.

The damage causes the walls of the bronchioles and alveoli to:

• Lose elasticity
• Collapse
• Swell
• Produce mucus

The above changes lead to obstructed, or blocked, bronchioles and alveoli. Air does not enter or exit the lungs freely, and the lungs are unable to take in oxygen as effectively as undamaged lungs. COPD causes symptoms of chronic bronchitis.