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The building elements of the airways

There is no cartilage in small intrapulmonary airways.

Cartilagenous and non-cartilagenous airways

Cartilage

Cartilage is limited to the large airways, and the proportion of the airway wall occupied by cartilage varies with the airway size. The cartilage in the airway wall can limit the degree of airway narrowing associated with airway smooth muscle contraction. The cartilage can be an afterload to the airway smooth muscle, and the cartilage can occupy a portion of the airway circumference that is not smooth muscle and thus can not shorten. Contraction of airway smooth muscles can only decrease the proportion of the airway circumference that is free of cartilage. Airway narrowing is proportionally greater in the small non-cartilagenous intrapulmonary airways than in the large cartilagenous airways.

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