Inside Your Body

Right now, while you are listening to this, something incredible is happening. Your heart is beating. Your lungs are filling with air. Your brain is processing every single word. Millions of tiny cells are working all at once, without you having to think about it at all. Your body is one of the most amazing machines that has ever existed, and you carry it with you everywhere. Welcome to the journey inside your body!

Let us start with your heart. It is a muscle, about the size of your clenched fist, and it works every single second of your life, day and night, without ever taking a break. Each beat pushes blood out to every part of your body. Your heart beats about seventy times a minute when you sit still, and it nearly doubles its pace when you run. Place your hand on your chest and feel it, your most loyal friend who never takes a day off.

And it pumps enormous amounts of blood. Every minute, your heart pumps about five litres of blood. In a single hour that is enough to fill two bathtubs! Across a whole day, your heart moves enough blood to fill about a hundred bathtubs. Over an entire lifetime, it pumps enough blood to fill thousands of swimming pools. And it does all this without ever taking a break, not even when you sleep. It all travels through a network of vessels, blood vessels, that run all through your body. If you could lay all your blood vessels end to end, they would stretch almost twice around the whole Earth.

What is blood, exactly? It looks red, but why? Blood is made up of millions of tiny red blood cells. Each red blood cell carries oxygen, which it picks up in the lungs and then delivers all around the body. It is the iron in those cells that gives blood its red colour. Along with the red cells, there are also white blood cells, and they have a completely different mission. They are your body's defence force, always ready to fight off intruders.