A long-term smoker develops a chronic cough and frequent respiratory infections. Which physiological change in the respiratory tract primarily contributes to this increased susceptibility?
Destruction of cilia in the upper respiratory tract
The upper respiratory tract is lined with cilia and mucus that trap dust, smoke particles and germs and sweep them up to the throat, where they are swallowed or coughed out. Long-term smoking paralyses and eventually destroys these cilia, so this cleaning escalator stops working. Trapped bacteria and particles now sit in the airways and cause repeated infections and a chronic cough.
Thickening of bronchial walls, narrowing of bronchi and increased mucus production do develop in smokers and add to breathlessness, but on their own they do not explain the sharp rise in infections. The rise in infections is due primarily to the loss of the mucociliary defence when the cilia are destroyed.
Hence, the answer is Destruction of cilia in the upper respiratory tract.
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