Need-to-know anatomy

Asthma is a disease of the bronchial tubes, the airways of the lungs. When air is taken into the body through the nose and windpipe, it passes through the bronchial tubes and smaller bronchioles into tiny air sacs, called alveoli, that deliver oxygen to the blood. The air sacs also collect carbon dioxide from the blood, which is then exhaled.

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During normal breathing, the bands of muscle that surround the airways are relaxed, and air moves freely. During an asthma episode, or "attack," three main changes stop air from moving easily through the airways:

• The bands of muscle that surround the airways tighten, narrowing the airways. This tightening is called a bronchospasm.
• The lining of the airways becomes swollen or inflamed.
• The cells that line the airways produce more mucous, which is thicker than normal.

Bronchospasms, inflammation, and mucus production cause asthma symptoms, which include wheezing, coughing, breathlessness, chest pressure, pain, or tightness. Severe episodes can lead to inability to perform normal activities like walking and talking.