The tertiary bronchi (also known as the segmental bronchi) arise from the secondary bronchi. The respiratory epithelium lining their lumen is surrounded by a layer of smooth muscle. This layer is composed of two ribbons of smooth muscle that spiral in opposite directions. The smooth muscle layer is surrounded by irregular plates of hyaline cartilage which help maintain the patency of the airway.

Each of the tertiary bronchi serves a specific bronchopulmonary segment. There are 10 bronchopulmonary segments per lung, each of which is separated from the others by a layer of connective tissue. This means that each bronchopulmonary segment is a discrete anatomical and functional unit, and this separation mean that a bronchopulmonary segment can be surgically removed without affecting the function of the other segments. The tertiary bronchi get smaller and divide into primary bronchioles.

References

Gartner, Leslie P. and James L. Hiatt. Color Textbook of Histology, 2nd ed. (2001). ISBN 0-7216-8806-3

Respiratory system Human anatomy Thorax