During normal breathing, air travels through the nose, down the trachea, and into smaller and smaller airways called bronchi. Bronchi divide into bronchioles and finally into tiny grape-like clusters of thin, fragile sacs called alveoli.

Chronic obstructive pulmonary disease, or COPD, refers to a group of diseases that cause airflow blockage and breathing-related problems.

Emphysema is a disease that destroys the alveoli and the alveolar ducts. As your lungs lose elasticity, the alveoli rupture, creating large airspaces that reduce the surface area needed by your body to absorb oxygen and remove carbon dioxide waste.

Bronchitis is the inflammation of the lining of the bronchial tubes. Chronic bronchitis results from the persistent inflammation of these airways. Mucus is continually produced and over time, the lining of the bronchial tubes become thickened. This restricts the flow of air during breathing. COPD is caused by tobacco smoke, exposure to air pollutants in the home and workplace, and genetic factors also play a role.