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Structural changes and pathogenesis of COPD. (A): Alveolar structure in normal lung and COPD lung. The lung is composed of millions of alveoli surrounded by a capillary network. Alveolar destruction and small airway obstruction are seen in COPD lung. (B): Mechanisms of airflow limitation in COPD. Insufficient repair capacity of lung endogenous stem cells may cause the alveolar destruction. Abbreviations: COPD, chronic obstructive pulmonary disease; CT, computed tomography.
