The lung is a complex organ composed of various cell types and structures. The main functional unit is the alveolus, where gas exchange occurs. Alveoli are lined by type I and type II alveolar cells. Type I cells are thin and facilitate gas diffusion, while type II cells secrete surfactant to reduce surface tension. Surrounding the alveoli are capillaries, supported by a delicate connective tissue matrix. The bronchi and bronchioles, lined by ciliated pseudostratified columnar epithelium, conduct air to the alveoli.
