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Pathology
Chronic obstructive pulmonary disease (COPD) is characterised by poorly reversible airflow obstruction and an abnormal inflammatory response in the lungs. The latter represents the innate and adaptive immune responses to long term exposure to noxious particles and gases, particularly cigarette smoke. All cigarette smokers have some inflammation in their lungs, but those who develop COPD have an enhanced or abnormal response to inhaling toxic agents. This amplified response may result in mucous hypersecretion (chronic bronchitis), tissue destruction (emphysema), and disruption of normal repair and defence mechanisms causing small airway inflammation and fibrosis (bronchiolitis).
These pathological changes result in increased resistance to airflow in the small conducting airways, increased compliance of the lungs, air trapping, and progressive airflow obstruction-all characteristic features of COPD. We have good understanding of the cellular and molecular mechanisms underlying the pathological changes found in COPD.
Proximal cartilaginous airways (>2 mm in diameter) |
[black square] Increased numbers of macrophages and CD8 T lymphocytes |
[black square] Few neutrophils and eosinophils (neutrophils increase with progressive disease) |
[black square] Submucosal bronchial gland enlargement and goblet cell metaplasia (results in excessive mucous production or chronic bronchitis) |
[black square] Cellular infiltrates (neutrophils and lymphocytes) of bronchial glands |
[black square] Airway epithelial squamous metaplasia, ciliary dysfunction, hypertrophy of smooth muscle and connective tissue |
Peripheral airways (non-cartilaginous airways <2 mm diameter) |
[black square] Increased numbers of macrophages and T lymphocytes (CD8 > CD4) |
[black square] Increased numbers of B lymphocytes, lymphoid follicles, and fibroblasts |
[black square] Few neutrophils or eosinophils |
[black square] Bronchiolitis at an early stage |
[black square] Luminal and inflammatory exudates |
[black square] Pathological extension of goblet cells and squamous metaplasia into peripheral airways |
[black square] Peribronchial fibrosis and airway narrowing with progressive disease |
Lung parenchyma (respiratory bronchioles and alveoli) |
[black square] Increased numbers of macrophages and CD8 T lymphocytes |
[black square] Alveolar wall destruction from loss of epithelial and endothelial cells |
[black square] Development of emphysema (abnormal enlargement of airspaces distal to terminal bronchioles) |
[black square] Microscopic emphysematous changes: Centrilobular-dilatation and destruction of respiratory bronchioles (commonly found in smokers and predominantly in upper zones) Panacinar-destruction of the whole acinus (commonly found in α1 antitrypsin deficiency and more common in lower zones) |
[black square] Macroscopic emphysematous changes: Microscopic changes progress to bulla formation (defined as... |