Tertiary Bronchi
The lungs' tertiary bronchi are also called the segmental bronchi. They branch out from the secondary bronchi, which descend from the mainstream bronchi. Lower in the lung, they become smaller and break up into the primary bronchioles. Each tertiary bronchus serves a particular bronchopulmonary segment. The left lung has nine tertiary bronchi, while the right lung has ten. A smooth muscle layer surrounds the respiratory epithelium, a type of moist, ciliated tissue lining the tertiary bronchi's lumen. This layer is made up of two muscular ribbons that spiral in opposite directions. Irregular plates of hyaline cartilage in turn, surround this layer of smooth muscle; these help keep the airway open.
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