In normal, quiet breathing, oxygen enters the trachea through the mouth and nose, and travels through the trachea and branching airways called bronchi and bronchioles until it reaches tiny sac-like structures called alveoli. At the alveoli, oxygen is delivered to tiny capillaries that will eventually carry it to the heart to be distributed to the rest of the body. Also at the alveoli, the tiny capillaries drop off carbon dioxide to be exhaled, thus preventing a build up of the gas.
Bronchioles that the oxygen must travel through are wrapped with smooth muscles. Asthmatic patients have bronchial smooth muscle that is more irritable than a normal patientís. When this muscle is irritated by a trigger, it constricts, decreasing the diameter of the airway. In addition to bronchoconstriction, when the asthmatic patient is exposed to a trigger, the airway also becomes very inflamed, and produces more mucus than normal.
There are three main characteristics of asthma:
A fourth component, Airway Wall Remodeling may be seen if asthma is inadequately treated.
In inflammation, the lining of the airways becomes swollen, and produces mucus. In asthma patients, the inflammation in the bronchi is an overreaction to triggers.
In hyperresponsiveness, the airways in the lung (the bronchi) have an exaggerated response, more than normal.
The result of this inflammation and hyperresponse for asthma patients is constricted airways that carry less oxygen to the alveoli.
Video explaining what asthma is.