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Medical Definition of Left main bronchus
1. It arises at the bifurcation of the trachea, passes in front of the oesophagus and enters the hilum of the left lung where it divides into a superior lobe bronchus and an inferior lobe bronchus. It is longer, of narrower caliber, and more nearly-horizontal than the right main bronchus, hence, aspirated objects enter it less frequently. Synonym: bronchus principalis sinister. (05 Mar 2000)