Skip to content
    • Biology Biology
    • Ico Science Science
    • Ico Human Biology Human biology
    • 11-14
    • 60


  of  3

What is asthma?

Both the lungs and the breathing system have adapted over time to ensure that breathing and gaseous exchange are efficient. You can find out more about gaseous exchange and the adaptations of the lungs in the gaseous exchange resource, and more about the breathing system in the breathing system resource.  

Asthma is primarily a condition which affects the breathing system since the airways of the lungs become narrower and this causes difficulty breathing. People with asthma have over-sensitive airways that become irritated by triggers such as pollen, house dust mites, pet hairs, exercise, smoke or even cold air. Asthma can also be triggered by stress. Someone who has asthma isn’t affected all the time. They may have attacks several times a day or only a few times a year.

Contraction Of Bronch Muscles



During an asthma attack the cells lining the bronchioles release chemicals called histamines. Histamines cause the lining of the cells to become inflamed, produce large amounts of mucus and swell. Histamines also make the muscles in the walls of the bronchioles contract. As a result of all these changes the airways narrow, making it very difficult to move air into and out of the lungs. 

This can lead to a tight chest and shortness of breath which therefore means that gaseous exchange is reduced, but indirectly. The tight chest reduces the efficiency of the breathing system, so there is insufficient airflow into and out of the alveoli. This results in poorer gaseous exchange.