Chronic bronchitis
- Lesion
Chronic bronchitis is a productive cough on most days for months each year, caused mostly by smoking that enlarges the mucus glands.
What it is
Chronic bronchitis is defined clinically: persistent cough with sputum for at least three months in two consecutive years, with no other cause. Its lesion is enlargement of the submucosal mucous glands of the trachea and bronchi, plus goblet cells and inflammation in small airways. It travels with emphysema under the name COPD, and in advanced cases it leads to hypoxaemia, pulmonary hypertension and cor pulmonale.
Structure
- Gross: red, swollen, edematous mucosa covered by mucinous or mucopurulent secretions; casts may fill the bronchi.
- Microscopy: enlarged submucosal mucous glands (high Reid index), goblet-cell hyperplasia, chronic inflammation (lymphocytes, macrophages).
- Small airways: smooth muscle hypertrophy, peribronchiolar fibrosis, mucus plugs and, in severe cases, bronchiolitis obliterans.
- Epithelium: squamous metaplasia and sometimes dysplasia.
Step by step
- Inhaled irritants (tobacco smoke, grain, cotton or silica dust, sulfur and nitrogen dioxides) injure the airway lining.
- Mediators such as IL-13 and histamine make the submucosal glands enlarge and secrete more mucus.
- Goblet cells multiply in the small airways and add mucus where there should be little.
- Smoke paralyses cilia and impairs CFTR, so the mucus is thick and stays.
- Chronic inflammation and fibrosis narrow the small airways: fixed obstruction.
- Infection does not start the disease but keeps it going and causes exacerbations.
Chronic bronchitis vs emphysema
| Feature | Chronic bronchitis | Emphysema |
|---|---|---|
| Lesion | Mucous gland enlargement, small-airway inflammation | Destroyed alveolar walls distal to the terminal bronchiole |
| Defined by | Clinical history of productive cough | Anatomy (pathology or imaging) |
| Cough and sputum | Early, copious | Late, scanty |
| Dyspnoea | Mild, late | Severe, early |
| Blood gases | Hypoxaemia and hypercapnia early: cyanosis | Near normal at rest until late |
| Cor pulmonale | Common | Uncommon, end-stage |
Clinical notes
- Most patients have a long heavy smoking history; spirometry shows FEV1/FVC below about 0.7.
- Symptoms worse in the morning; exacerbations with viral or bacterial infection (H. influenzae, M. catarrhalis, pneumococcus).
- Death from cor pulmonale, respiratory failure during infection, or lung cancer.
Test yourself
Think of the answer, then tap the question to see it.
How is chronic bronchitis defined?
A persistent productive cough for at least three months in at least two consecutive years, with no other identifiable cause.
What does the Reid index measure?
The ratio of the thickness of the mucous gland layer to the thickness of the bronchial wall between epithelium and cartilage; it rises in chronic bronchitis.
Why does chronic bronchitis lead to cor pulmonale more often than emphysema?
Patients are hypoxaemic early; chronic hypoxia constricts and remodels pulmonary arteries, causing pulmonary hypertension and right heart failure.
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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: COPD (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.