Asthma pathology and treatment, cutaway diagrams. At right is an asthmatic patient using an inhaler to apply bronchodilator drugs to treat his asthma. The drugs (red arrows) are breathed in through the mouth, down the trachea and into the two lungs. The diagrams at left show cross-sections through a normal airway (top) and an asthmatic, constricted airway (bottom). The airways have a ring of smooth muscle (brown) and an inner layer of endothelial tissue (red/white). In the asthmatic airway, the smooth muscle has contracted, and the tissue is inflamed. Endothelial cell debris and mucus (blue) are blocking the airway. The bronchodilator drugs widen the airway, making it easier to breathe.