How the body copes with extremes of temperature. Humans live in some extraordinary places –from the middle of the Sahara desert to the frozen wastelands of Alaska. Take a snake to the North Pole, and it will stop moving in minutes; take a cat to the desert and it will be dead in hours. So how can some humans survive such extremes, and could anyone? Dr Montgomery explains how our bodies burn fuel using oxygen to create an energy currency, which in turn creates heat. Viewers will discover whether shivering really works, whether a hot meal makes a difference to our internal body temperature and whether mothers are right when they say that you should wear a hat on a cold day. But what about when it is too hot? Where is the blood diverted in order to cool the body down? What is sweat and how does it work? And why do dogs pant, and humans not? Finally, Dr Montgomery meets some people who have survived in the very coldest places and the hottest places on Earth. What are the limits to human survival, and how close did these people come to death?

• Helen Czerski
• Kevin Fong
• Tara Shine