Bronchioles are small air passages in the lungs that branch off from the larger bronchi. They play a crucial role in the respiratory system by directing air to the alveoli, where gas exchange occurs. Unlike bronchi, bronchioles do not have cartilage in their walls, making them more flexible and able to constrict or dilate. These tiny tubes are lined with smooth muscle and are responsible for regulating airflow. When the body needs more oxygen, the bronchioles can widen to allow more air in. Conversely, they can narrow during conditions like asthma, which can restrict airflow and make breathing difficult.