Blood: Your Body's River

Blood is a remarkable liquid that flows through every part of your body. It is made in the soft spongy material inside your bones called bone marrow, and it carries out dozens of jobs all at once. Think of it as a busy river delivering parcels everywhere.

Blood is not just a plain red liquid — it is made of several different parts mixed together, and each part has its own special job. If you let blood settle, it would separate into layers, a bit like oil and water in a bottle.

Red blood cells are the most common part. They carry oxygen from your lungs to every cell, then carry waste carbon dioxide back. There are so many of them that a single drop of blood holds millions. They are shaped like tiny squashed doughnuts to help them squeeze through narrow vessels.