Final answer:
Bronchioles differ from bronchi in that they lack cartilage, which is present in the bronchi to maintain their structure. Bronchioles have muscular walls that can adjust their diameter for airflow regulation, unlike the more rigid bronchi.
Step-by-step explanation:
The main difference between bronchioles and bronchi is that bronchioles lack cartilage in their structure, which is present in the bronchi. Bronchioles branch off from the tertiary bronchi and continue to divide into smaller tubes until they become terminal bronchioles, which then lead to the gas exchange structures. They are about 1 mm in diameter and are more than 1000 in each lung. The walls of bronchioles consist of smooth muscles that allow the diameter of these airways to change to regulate the airflow. This feature enables the respiratory system to control the resistance and distribution of air reaching the alveoli, where gas exchange occurs. In contrast to the bronchi, which have rigid cartilage in their walls to maintain their shape, bronchioles rely on the elastic fibers and inhaled air to keep them open.