Asthma pathology, comparative illustrations. The artworks show cross-sections through a normal airway (top) and an asthmatic, constricted airway (bottom). The airways have a ring of smooth muscle and a thin layer of endothelial tissue. In the asthmatic airway, the smooth muscle has contracted, and the tissue is inflamed. Endothelial cell debris and mucus are blocking the airway. Bronchodilator drugs widen the airway, making it easier to breathe.