Merck Manual

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How Airways Narrow
How Airways Narrow
How Airways Narrow

In asthma, inhalation of certain stimuli (for example, pollen, smoke particles, cold air) may cause the smooth muscle of the bronchi to spasm. The tissues lining the airways (mucosa) become inflamed and swell. Mucus may be secreted, which plugs the airways. All of these effects reduce the diameter of the airways.

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Asthma