The pathology of asthma.

The airways smooth muscle is increased in amount in asthma and may be of a type that shows more spontaneous activity and a greater tendency to contract when it is stretched. The increased airways reactivity and easily reversible bronchoconstriction of mild asthmatics is probably associated with a mild inflammatory reaction in the airways. As the asthmatic condition progresses this inflammatory reaction becomes more severe. This is associated with sloughing of the epithelial layer and regeneration of the basal epithelial cells that leads to thickening of the epithelial basement membrane as well as goblet cell and squamous cell metaplasia. This inflammatory reaction is associated with excess production of mucus by both mucus glands and goblet cells and an interference with normal airway clearance so that the same airways become occluded with inflammatory mucus plugs. When this mucus plugging becomes extensive, the patient's life is at greater risk because even the most minor muscle constriction on top of these plugs can lead to complete airway occlusion.