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.

White blood cells are your body's soldiers. There are fewer of them than red cells, but they are mighty defenders that hunt down germs and destroy them. Platelets are tiny pieces that rush to a cut and stick together to plug the gap, which is how a scab forms.

Plasma is the pale yellow liquid that all the cells float in. It is mostly water, and it carries the cells along as well as delivering food, vitamins and important messages to the parts of your body that need them.

Blood travels through three types of vessels. Arteries carry blood away from the heart under high pressure. Veins carry blood back to the heart. Capillaries are tiny, hair-thin tubes that reach every single cell to make their deliveries. Together they form an enormous network.

When you cut yourself, it can look alarming, but your blood is brilliant at fixing things. Platelets and special proteins quickly form a clot to stop the bleeding, then a scab forms to protect the wound while new skin grows underneath. Eating iron-rich foods like green vegetables helps your body make healthy blood.