Pulmonary alveoli
The pulmonary alveoli are tiny sacs located at the end of the bronchioles, with very thin walls, surrounded by numerous blood capillaries, which allow the exchange of gases between the air and the blood.
Each person has about 400 million pulmonary alveoli, which allows to have a respiratory surface to exchange gases of about 100 m2.
Activity: Pulmonary alveoli.
Pleura
The pleurae are two membranes that surround the lungs and that have a fluid between them that allows the lungs to slide into the chest cavity during respiratory movements.

By Cancer Research UK uploader (Own work) [CC BY-SA 4.0], via Wikimedia Commons
Activity: A system of ducts carries air from the atmosphere to the blood.
Activity: The lungs.
Activity: Parts of the lungs. (No registration required)
Activity: Parts of the respiratory system.
Activity: Anatomy of the respiratory system.
Activity: The respiratory system.
Activity: The respiratory system.
Animation: Basic aspects of breathing.
Game: Parts of the respiratory system.
3D model: Anatomy of the lung.
Do it yourself: Inflatable lung model.