Alice Bope, aged 9, of Somerset, Ohio for her question:

How does the blood travel from the feet back to the heart?

It is easy to understand how the blood gets from the heart to the feet. The pumping heart sends it on its way. What's more it runs downhill. Getting back to the heart must be quite a problem,. For the blood must run uphill most of the time. But it makes the round trip very well.

Blood is carried back to the heart by veins. These blood vessels have many little built‑in valves. These valves prevent the blood from flowing away from the heart. They help to keep it traveling in the right direction.

The branching of the veins also helps to push the blood back to the heart. The return trip starts in a fine mesh of tiny blood vessels, These fine veins ,loin together to form larger veins. This joining up of little streams helps speed up the flow.

At the same time, the heart is still pumping out fresh blood. This shoves at the returning blood from behind. So the wonderful body combines three tricks to keep the used blood flowing back to the heart. Together they are strong enough to keep the used blood flowing uphill even from the toes.