This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
[{'content': 'Respiratory bronchiole proceed into: \nSelect and explain. \nA. Terminal bronchiole, B. Bronchi, C. Tertiary bronchiole, D. Alveolar duct', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Bronchioles have a diameter smaller than 1 mm and lack cartilage and glands within their walls. Goblet cells (and cilia) decrease in\xa0number and almost negligible at the levels of bronchioles (small lumen). Hyaline cartilage also is almost non-existent at the levels of\xa0bronchioles. Epithelium gradually changes from pseudostratified columnar to simple columnar to cuboidal to squamous.\nAlveolus is lined by type-I pneumocyte (simple squamous epithelium) for respiratory gas exchange. Type- II pneumocyte is a cuboidal\xa0cell for surfactant secretion.\nBronchial arteries (branches of descending thoracic aorta) supply till the level of respiratory bronchiole. They perfuse the proximal air\xa0conducting pathways including tertiary and terminal bronchioles and reach till the beginning of respiratory unit. Pulmonary arteries\xa0alone vascularize the further distal pathways, including alveolar ducts and the alveoli.', 'role': 'assistant'}]