Final answer:
The bronchial tree consists of the bronchi and bronchioles, which transport air within the lungs. While the bronchi contain cartilage to stay open, bronchioles lack cartilage and are supported by elastic fibers. Bronchioles regulate airflow with their smooth muscle and are flexible due to the absence of cartilage.
Step-by-step explanation:
The bronchi and bronchioles form a branching system known as the bronchial tree, which serves as a network for air transport within the lungs. The trachea divides into the primary bronchi that enter the lungs, which further divide into secondary and tertiary bronchi. Eventually, these bronchi become progressively smaller in diameter as they branch into bronchioles.
The bronchi have a structure composed of cartilage and smooth muscle, ensuring that they remain open and do not collapse. The bronchioles, however, are unique because they do not contain cartilage. Instead, they are supported by elastic fibers and smooth muscle, making them flexible and capable of changing diameter to regulate airflow. This anatomical characteristic of bronchioles allows them to rely on inhaled air to maintain their shape, particularly when the diameter of the bronchioles is less than 0.5 mm; at this point, they are referred to as respiratory bronchioles.