Asthma. Cut-away illustration of the respiratory system showing the effects of asthma. The trachea (windpipe) is at top and the alveoli, air sacs (white), are at bottom. At upper right the cut- away bronchioles reveal their excessive sputum, or phlegm (green). In asthma, a trigger, such as an allergen, causes bronchiole narrowing, resulting in inflammation and shortness of breath. In response, mucus-producing goblet cells (one seen magnified at upper centre) produce too much sputum. This coats the tentacle-like cilia of the bronchiole lining (epithelium). Alternatively the artwork may represent bronchitis, where infection or irritation cause inflammation directly.

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