Branching in the Human Lung 
Number Generation Region 
Figure 1.9.1-B. Branching in the normal human lung. The conducting zone 
represents the region from the trachea through generation 16. The bronchi 
start at generation 1 and go through generation 16 while the bronchioles 
start at generation 17 and go through generation 20. By the end of the 
conduction zone there are approximately 1,000,000 bronchioles. 
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