Image: http://www.nhlbi.nih.gov/health/dci/Diseases/Asthma/Asthma_WhatIs.html

Figure A: location of lungs in the body and airways in the lungs.

Figure B: a normal, non-asthmatic airway.

Figure C: an airway during asthmatic symptoms.  The airway is narrowed, limiting air flow.  Tightened muscles constrict air flow, as do inflamed and thickened airways.  Excess mucus clogs the airway.