Lower - 

Trachea: The trachea is attached to the cricoid cartilage of the larynx. It is a mucocartilagenous tube that is completed posteriorly by smooth trachealis muscle. The hyaline cartilage rings prevents the airways from collapsing during inspiration. Along the convexity of the C-shaped rings, the adventitia contains numerous adipocytes, blood vessels and nerves, and blends with the perichondrium of the hyaline cartilage.

In the concavity of the cartilaginous rings, the submucosa has numerous seromucous glands, blood vessels, loose connective tissue fibers and scattered lymphatic tissue. The lumen of the trachea has numerous mucosal folds along the posterior wall, where there is no hyaline cartilage.

Larynx: Pseudostratified columnar ciliated epithelium with seromucous glands in its lamina propria continues in to the larynx and covers the false vocal fold and the end of the laryngeal ventricle. Goblet cells, seromucous glands, lymphatic nodules and adipocytes are observed throughout the lamina propria to the end of the ventricle. The cilia assists in retaining the mucous lining, which helps to reduce damage caused during phonation.

Bronchioles: Terminal bronchioles then branch to form respiratory bronchioles. This marks the transition point from the conducting to the respiratory portion of the respiratory system. The epithelium here is simple cuboidal that may be ciliated proximally, but devoid of cilia distally. The smooth muscle layer is thinner here than in the conducting portion.