There are trillions of cells in our bodies, each one needing oxygen to survive. This book explores how the heart, lungs and blood work together to supply oxygen to the rest of the body. Mind-boggling facts (for instance, your blood vessels are long enough to stretch around the world two and half times!), and clear and straighforward diagrams help to explain the important functions of your heart, lungs and blood, while unique photos enable the reader to see the human body in a whole new light.