At which site in the tracheobronchial tree is total airway resistance greatest in a healthy adult?
- A Terminal bronchioles
- B Alveolar ducts
- C Medium-sized bronchi ✓
- D Respiratory bronchioles
Correct answer: C. Medium-sized bronchi
Explanation
Although each medium-sized bronchus is wider than a terminal bronchiole, the very large number of peripheral airways arranged in parallel gives them an enormous combined cross-sectional area, so individually narrow small airways contribute surprisingly little to total resistance. Peak resistance therefore sits in the segmental and subsegmental bronchi around the fourth to eighth generations. This is why small-airway disease is silent until advanced.
Reference: West's Respiratory Physiology: The Essentials, 10th ed.
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