Dr Montgomery examines the theme of respiration. Just like racing car engines, humans use oxygen to burn fuels and release the energy that powers each function in every cell. So how do we get the oxygen from the air to the cell, and what happens when oxygen levels in the air are dramatically reduced? Dr Montgomery looks at the airways that carry the oxygen, and the rib-and-muscle bellows which drive air through them. He examines the lung and explains how it passes the oxygen on to the blood cells which grab and hold that oxygen. Then, viewers are shown how the heart pumps these cells around the body through a complex system of blood vessels, where the oxygen is passed onto the cells for another phase of processing. In the second half of the lecture, Dr Montgomery meets some mountaineers who have climbed Everest where there is three-times less oxygen than at sea level. What happens to these people’s bodies when they struggle to stand at the very top of the world?