Causes of asthma

Bronchiole Narrowing, Mucus Buildup

In asthma, when the bronchioles are exposed to an irritating substance, they respond by closing down or narrowing. This leaves much less room for the passage of air into the lungs. The irritated bronchioles also fill up with mucus, which is filled with immune cells that the body has released in an effort to get rid of the irritating substance. But instead, the mucus buildup leads to further bronchiole obstruction and narrowing. The bronchiole narrowing and mucus buildup cause the breathing difficulties of asthma, which can become a medical emergency requiring treatment in a hospital.