How Air Leaves the Lungs: Bronchioles vs. Large Airways
Bronchioles do not "release" air; they are conducting airways (≤2 mm diameter) that transport air to and from the alveoli. During exhalation, the majority of expired air volume moves through the larger airways—trachea and main bronchi—because they offer the least resistance and have the greatest cross-sectional area proximally.
Airflow Path
- Alveoli → respiratory bronchioles → terminal bronchioles → bronchi → trachea → larynx → pharynx → atmosphere.
- Gas exchange occurs only in respiratory bronchioles, alveolar ducts, and alveoli.
- Bronchioles lack cartilage; rely on radial traction from elastic lung tissue for patency.
Key Concept
Exhalation is passive (elastic recoil) at rest; forced exhalation recruits abdominal/internal intercostal muscles. Airflow limitation in diseases like asthma/COPD occurs primarily at the small airway level (bronchioles), but the volume of air expelled still traverses the large airways.
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