Question

If we were to examine cross-sections of the primary bronchi, then secondary, then tertiary, and finally the respiratory bronchioles, we would notice __________.

Answer 1

In examining cross-sections of the lung's bronchial tree, from primary bronchi to respiratory bronchioles, a transition from cartilaginous to elastic structures is observed, with an increase in smooth muscle as the airways get smaller.

Step-by-step explanation:

If we were to examine cross-sections of the primary bronchi, then secondary, then tertiary, and finally the respiratory bronchioles, we would notice a gradual change in the structure of the airways. The primary bronchi are made of cartilage and smooth muscle, similar to the trachea. As we move from the primary to the secondary and tertiary bronchi, the bronchi continue to branch into smaller and smaller bronchioles. These bronchioles lead to even tinier terminal bronchioles, which in turn lead to the alveoli, where gas exchange occurs.

Throughout this progression, the relative amount of smooth muscle increases as the passages decrease in size, and the cartilage that supports the larger airways is replaced with elastic fibers in the smaller bronchioles. Unlike bronchi, these bronchioles do not contain cartilage and rely instead on inhaled air to maintain their shape.

Additionally, the bronchi and bronchioles are innervated by autonomic nervous system fibers from both the parasympathetic and sympathetic systems, which control the diameter of the airways by contracting or relaxing the smooth muscle.