Figure 1-3. The respiratory system.
e. Trachea. The trachea (windpipe) is a tube composed of horseshoe-shaped
rings of cartilage. Cilia (hair-like projections) on the inner lining of the trachea help to
filter air as it passes through the trachea to the bronchi.
f. Bronchi. The bronchi are two tube-like structures at the base of the trachea.
One bronchus leads toward the right lung; the other bronchus leads toward the left lung.
Like the trachea, the bronchi are composed of cartilaginous rings and are lined with a
g. Bronchioli. The bronchi divide and subdivide until they become small air
tubes one millimeter or less in diameter call bronchioli. The bronchioli continue to
subdivide until they become very small tubes ending in alveoli.