The lungs resemble an upside-down tree. The “trunk” is called the trachea, which leads from the throat into the chest. The trachea narrows into “branches” called bronchi. They in turn taper down into “twigs” called small bronchi and then bronchioles. Last, there are “leaves” – small sacs called alveoli where the blood exchanges carbon dioxide for fresh oxygen.
All the bronchi are surrounded by smooth muscle along with mucous glands. When the smooth muscle contracts, it leads to constriction, or narrowing, of the airways. This bronchoconstriction contributes to the airway obstruction known as asthma. When constriction is severe, the patient starts to feel that she cannot breathe.
The lungs, in turn, may not be able to supply the blood with as much fresh oxygen as the body needs.
The other factors are the edema, or swelling, of the lining of the airways, which can damage it, as well as the increase in mucus.