4.7
Chronic bronchitis, a major phenotype of COPD, results from prolonged exposure to airborne irritants such as cigarette smoke.
These irritants trigger persistent inflammation that begins in the larger bronchi and extends into the smaller airways.
Neutrophils, macrophages, and lymphocytes infiltrate the bronchial walls, causing epithelial injury.
Inflammation also causes squamous metaplasia, which replaces the ciliated epithelium with squamous cells, impairing mucociliary clearance.
Meanwhile, goblet cells and submucosal glands undergo hyperplasia and hypertrophy, producing thick mucus that clogs the airways and promotes infection.
Persistent inflammation and mucus plugging lead to airway remodeling, including smooth muscle hypertrophy and fibrosis, which narrow the airways, especially during expiration.
Airway obstruction creates a ventilation–perfusion mismatch, leading to hypoxemia. Progressive air trapping causes hyperinflation, which flattens the diaphragm, reduces ventilatory efficiency, and increases the work of breathing.
Chronic bronchitis is a key phenotype of chronic obstructive pulmonary disease (COPD), characterized by airway-centered inflammation and mucus overproduction. It develops from long-term exposure to harmful particles or gases, most commonly cigarette smoke, which triggers a persistent inflammatory response.
Inflammation initially affects the large bronchi and later the smaller airways, with infiltration by immune cells, including neutrophils, macrophages, and lymphocytes. The airway epithelium undergoes squamous metaplasia, replacing ciliated cells with non-ciliated squamous cells, which impair mucociliary clearance and increase infection risk. Simultaneously, submucosal glands and goblet cells enlarge (hyperplasia and hypertrophy), producing excessive, thick mucus. This is reflected in an increased Reid index, with glands occupying over half the thickness of the bronchial wall. Mucus accumulation promotes bacterial colonization, recurrent infections, and ongoing airway damage.
Airway remodeling includes smooth muscle hypertrophy, fibrosis, and inflammatory thickening, narrowing airways—especially during expiration. Mucus plugs further obstruct bronchioles, causing airflow limitation, air trapping, and hyperinflation. This flattens the diaphragm, reduces tidal volume, and increases the work of breathing, sometimes producing a barrel-shaped chest.
Gas exchange is impaired due to ventilation–perfusion mismatch, where perfusion exceeds ventilation, leading to hypoxemia and, in advanced cases, hypercapnia due to poor carbon dioxide clearance.
These changes result in chronic productive cough, dyspnea, and frequent infections. Although lung parenchyma is relatively preserved compared to emphysema, progressive airway damage leads to declining lung function.
Chronic bronchitis, a major phenotype of COPD, results from prolonged exposure to airborne irritants such as cigarette smoke.
These irritants trigger persistent inflammation that begins in the larger bronchi and extends into the smaller airways.
Neutrophils, macrophages, and lymphocytes infiltrate the bronchial walls, causing epithelial injury.
Inflammation also causes squamous metaplasia, which replaces the ciliated epithelium with squamous cells, impairing mucociliary clearance.
Meanwhile, goblet cells and submucosal glands undergo hyperplasia and hypertrophy, producing thick mucus that clogs the airways and promotes infection.
Persistent inflammation and mucus plugging lead to airway remodeling, including smooth muscle hypertrophy and fibrosis, which narrow the airways, especially during expiration.
Airway obstruction creates a ventilation–perfusion mismatch, leading to hypoxemia. Progressive air trapping causes hyperinflation, which flattens the diaphragm, reduces ventilatory efficiency, and increases the work of breathing.
From Chapter 4:
Now Playing
Respiratory System Disorders
169 Views
Respiratory System Disorders
613 Views
Respiratory System Disorders
226 Views
Respiratory System Disorders
2.9K Views
Respiratory System Disorders
256 Views
Respiratory System Disorders
170 Views
Respiratory System Disorders
2.9K Views
Respiratory System Disorders
108 Views
Respiratory System Disorders
305 Views
Respiratory System Disorders
167 Views
Respiratory System Disorders
130 Views