Asthma pathology. Computer artwork showing 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 enlarged and contracted, and the tissue is inflamed (oedematous). Endothelial cell debris and mucus (blue) are blocking the airway. Bronchodilator drugs are used to widen the airway, making it easier to breathe.