Final answer:
The bronchioles in the lower airways lack cartilage and are influenced by the autonomic nervous system to constrict or dilate depending on physiological demands for oxygen and carbon dioxide regulation.
Step-by-step explanation:
B. Bronchioles are the segments of the lower airways that lack cartilage and respond to neurotransmitters by constricting or dilating. The lower airways distribute air into smaller passages within the lungs. The primary bronchi split into secondary bronchi, then tertiary bronchi, and finally into bronchioles. The bronchi are supported by cartilage and smooth muscle, but as they branch into bronchioles, the cartilage gives way to elastic fibers. These bronchioles have muscular walls and are less than 1 mm in diameter at the terminal ends, lacking cartilage which would have given them rigidity.
The bronchioles are innervated by nerves of the parasympathetic and sympathetic nervous systems, which control the contraction or relaxation of the smooth muscles in the bronchioles, leading to constriction or dilation of the airway. Control of their constriction and dilation is exerted by the autonomic nervous system, with the parasympathetic system causing bronchoconstriction and the sympathetic system causing bronchodilation. This allows the bronchioles to respond dynamically to the body's demand for oxygen and the need to maintain proper levels of carbon dioxide.