Chronic bronchitis is the presence of cough productive of sputum for 3 months per year, in 2 consecutive years. In chronic bronchitis, tobacco smoke causes inflammatory cells (neutrophils and leukocytes) to arrive in the bronchi. These cells worsen airway obstruction by causing inflammation and thickening of the airways.
Also, mucus-producing glands deep within the lining of the airways become enlarged (hypertrophy) and increase in number (hyperplasia), and the number of surface cells that produce mucus (goblet cells) increases, resulting in excessive secretion of mucus in the lungs. The resulting chronic cough and expectoration affects the central conducting airway (see Anatomy of the Respiratory System).
The function of mucus in the lungs is to trap and clear particles, to dilute harmful substances, to lubricate the airways, and to humidify inspired air. In chronic bronchitis,
- the hyperplasia and hypertrophy of the submucosal glands (mucus-producing glands deep within bronchial walls) thicken the airway walls
- the resulting increased volume of mucus that occurs plugs the airways
- columnar cells (cells that line the surface of the airways) undergo changes that result in the destruction of ciliadelicate hairlike structures on columnar cells lining the airways that sweep mucus with offending agents up and out of the lungs. The loss of cilia and the inability to clear bacteria predispose the patient to lung infections.