(No Copyright)Schematic Explanation of Airway
Hyperreactivity
Two elements contributing to airway hyperreactivity in asthma are submucosal thickening and smooth muscle hypertrophy. The smooth muscle contracts against the resistance of the elastic recoil of the surrounding lung. For the same degree of stimulation, the hypertrophied smooth muscle is able to narrow the airway more than normal. When the smooth muscle shortens and decreases the circumference of the airway. The submucosa does not change in volume and must be accomodated by projections into the lumen. When the volume of the submucosa is increased (by inflammatory edema or fibrosis), the projections are larger and obstruct the lumen more. Thus these two abnormalities, smooth muscle hypertrophy and submucosal thickening act in concert to narrow the airway.
