BSIP VEM / SCIENCE PHOTO LIBRARY BSIP VEM / SCIENCE PHOTO LIBRARY
Asthma. Illustration showing the changes in the respiratory system during an asthma attack brought about by an allergic reaction. In the lung in the figure at left, air moves freely through small, branching airways called bronchioles. A bronchiole is shown in cross-section at upper right. However if an allergen is breathed into the lungs this triggers constriction of the bronchioles (as at centre right), leading to inflammation and the production of phlegm. The result is an attack of breathlessness and wheezing brought about by a lack of oxygen. The reduced lung function is represented in the figure at centre. The airways may be widened by inhaling bronchodilator drugs.
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