Asthma―a condition that afflicts hundreds of millions of people worldwide―has been recognized by physicians and lay people for more than two millennia. One would think that after all this time, and with so many affected people, we would understand the root causes of the disease. We don't; but we do know a little. Pathologically, asthma is characterized by infiltration of the airways with two specific types of immune cells. Physiologically, the disease features both the asthma attack itself (episodic obstruction of the airways) and bronchial hyperresponsiveness―the tendency of the airways to narrow when exposed to a stimulus, such as cold, dry air, that would be innocuous in a normal person. Genetically, asthma is known to be a heritable, complex disorder (although the underlying genes have not been pinpointed) that requires exposure to certain environmental factors before it is fully expressed.
展开▼
