Lung airway inflammation, comparative illustrations. The artworks show cross-sections through a normal airway (left) and an inflamed, constricted airway (right). The airways have a ring of smooth muscle and a thin layer of endothelial tissue. In the inflamed airway, the smooth muscle has contracted, and endothelial cell debris and mucus are partially blocking the airway. This is seen in conditions such as bronchitis and some forms of asthma. Drugs to treat the condition reduce the inflammation and widen the airways, making it easier to breathe.