Pulmonary path II: Obstructive Lung Diseases

Major obstructive lung diseases

Asthma, Chronic bronchitis, Emphysema, Bronchiectasis.

Asthma definition

Chronic inflammatory disorder with episodic, reversible bronchospasm causing airway obstruction.

Asthma immune pathogenesis

TH2-mediated(inhaled allergens): IL‑4 → IgE, IL5 activates eosinophils, IL13 stimulates mucous production

Immediate phase of asthma

Mast cell degranulation → bronchospasm, edema, mucus production.

Late phase of asthma

Eosinophil-mediated epithelial damage (major basic protein, Charcot‑Leyden crystals).

Asthma airway remodeling

Goblet cell metaplasia, smooth muscle hypertrophy/hyperplasia, submucosal gland enlargement, basement membrane thickening.

Classic sputum findings in asthma

Curschmann spirals(epithelium that has been shed) + Charcot‑Leyden crystals(destroyed eosinophils).

Triggers for atopic asthma

Allergens, dust, pollen, pets

Triggers for non-atopic asthma

Viral infections, pollutants, cold air, exercise

Chronic bronchitis definition

Productive cough ≥3 months per year for ≥2 consecutive years.

Chronic bronchitis pathogenesis

Smoking → mucous gland hyperplasia, goblet cell hyperplasia, CFTR dysfunction → dehydrated mucus.

Chronic bronchitis clinical features

Productive cough, wheezing, hypercapnia, hypoxemia, mild cyanosis (“blue bloater”).

Chronic bronchitis gross pathology

Hyperemia, edema, mucopurulent secretions filling bronchi.

Chronic bronchitis microscopic pathology

Mucinous gland hypertrophy/hyperplasia, chronic inflammation, fibrosis.

Emphysema definition

Permanent enlargement of airspaces distal to terminal bronchiole with destruction of septal walls without fibrosis.

Emphysema pathogenesis

Protease–antiprotease imbalance (↑neutrophil elastase, ↓A1AT), oxidative stress, inflammation»leads to destruction of septal walls and enlarged air space

Centriacinar emphysema

Smoking-related, upper lobes

Panacinar emphysema

A1AT deficiency, lower lobes

Emphysema clinical features

Dyspnea, prolonged expiration, barrel chest, “pink puffer.”

Emphysema gross pathology

Enlarged airspaces, apical blebs, bullae.

Emphysema microscopic pathology

Loss of alveolar septa, enlarged airspaces, minimal fibrosis.

Why emphysema causes air trapping

Loss of elastic recoil → airway collapse during exhalation.

COPD= (two diseases

Chronic bronchitis + emphysema causing airflow limitation

Blue bloater vs pink puffer

Blue bloater = chronic bronchitis (hypoxemia, hypercapnia). Pink puffer = emphysema (dyspnea, hyperventilation).

Bronchiectasis definition

Permanent dilation of bronchi/bronchioles due to inflammatory destruction of smooth muscle + elastic tissue.

Bronchiectasis pathogenesis

Chronic obstruction + infection → impaired clearance → inflammation → airway wall destruction.

Bronchiectasis clinical features

Chronic cough, foul-smelling sputum, hemoptysis, recurrent infections, worse in morning.

Bronchiectasis radiology

CXR: tram-track sign, peribronchial cuffing. CT: signet-ring sign, lack of tapering, airway visibility to periphery.

Bronchiectasis gross pathology

Dilated airways filled with pus