The respiratory fine bronchi are ciliated. The respiratory bronchioles are connected to the terminal bronchioles by a single layer of cuboidal epithelium with ciliated and secretory cells. The wall of the respiratory bronchioles is lined with alveolar openings, and the respiratory bronchioles are kept open by the traction of the surrounding tissues. The respiratory bronchioles are one of the places of gas exchange. Oxygen in the air during inhalation is diffused through the respiratory bronchioles into the pulmonary capillaries, while carbon dioxide in the pulmonary capillaries is diffused into the respiratory bronchioles, and then expelled from the body through the alveolar ducts, the alveoli, all levels of the bronchioles, and the main bronchioles. The cilia on the respiratory bronchioles oscillate and help to expel mucus secretions from the bronchioles. If the cilia of the respiratory bronchioles are damaged, sputum will be difficult to be discharged, blocking the airways and affecting the ventilation function of the lungs. If the cilia of the respiratory bronchioles function abnormally, it is recommended to consult a doctor for further examination and treatment as prescribed by the doctor.