Where does blood go?
Bloods travels around your body in a network of pipes called blood vessels. The blood vessels that carry blood away from the heart are called arteries, the one that carry it back again are called veins. Arteries and veins are connected to each other by more than 80 000 km (50 000 miles) of capillaries, tiny vessels much thinner than a hair. Arteries expand every time your heart beats. In places such as the wrist, this creates a 'pulse' you can feel.

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A single drop of blood contains about 250 million red cells and over 300 000 white cells. Red cells wear out quickly, and every day the blood makes about 2.5 billion new ones to replace them.