The composition of inhaled and exhaled air are compared and the anatomy of the respiratory surface is described. Using an animation, the presenters describe how gaseous exchange takes place. The function and importance of the alveoli are explained: large surface area, moist, thin walls, good blood supply.

First broadcast:
21 November 2008

As a group, explore the pathway of oxygenated and deoxygenated blood through the body. The structure of the lung should be looked at in more detail, using dissection and models to convey the concept of the large surface areas involved. Discuss gaseous exchange in the alveoli in terms of diffusion across cell membranes.