Secondary bronchi

Secondary bronchi (also known as lobar bronchi) arise from the primary bronchi, with each one conducting air to a specific lobe of the lung.

Secondary bronchi have relatively large lumens that are lined by respiratory epithelium. There is a smooth muscle layer below the epithelium arranged as two ribbons of muscle that spiral in opposite directions. This smooth muscle layer contains seromucous glands. Irregularly arranged plates of hyaline cartilage surround the smooth muscle. These plates give structural support to the secondary bronchus and maintain the patency of the lumen.

In the following image, number “3” points to the secondary bronchi (“1” is trachea and “2” is carina):