ANATOMY

Detailed explanation-1: -The trachea and bronchi (from the Greek bronkhos, meaning “windpipe") have cartilaginous walls. Bronchi undergo multiple divisions and eventually give rise to the terminal bronchioles, which by definition, lack cartilage. The most distal respiratory bronchioles and alveoli are in charge of gas exchange.

Detailed explanation-2: -Bronchioles. The bronchioles are the final air conductors, and by definition, lack cartilage altogether (and are therefore sometimes referred to as membranous) (Fig. 1.11). The bronchioles have no alveoli; alveoli are acquired more distally in the pulmonary acinus.

Detailed explanation-3: -As stated, these bronchioles do not have hyaline cartilage to maintain their patency. Instead, they rely on elastic fibers attached to the surrounding lung tissue for support. The inner lining (lamina propria) of these bronchioles is thin with no glands present, and is surrounded by a layer of smooth muscle.

Detailed explanation-4: -The trachea. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue.

Detailed explanation-5: -The mainstem bronchi give rise to secondary bronchi that branch about 9 to 12 times while extending into the lungs. These bronchi have cartilage arranged circumferentially in discontinuous plates. The cartilage keeps the bronchi stiff and open but provides flexibility.