Which organ pumps blood around the body?

The heart beats around 100,000 times a day and something like two and a half billion times in an average life, moving roughly 7,500 litres of blood every twenty-four hours through a vessel network which, laid end to end, would run tens of thousands of kilometres.

It does not need your brain's permission. The heart generates its own rhythm from a patch of specialised cells called the sinoatrial node, which is why a heart continues beating when removed from the body and kept supplied, and why heart cells grown in a dish will spontaneously start pulsing - and, if there are enough of them touching, gradually fall into step with each other.

One myth to dispose of. Deoxygenated blood is not blue. It is a dark red, and the reason veins look bluish through the skin is how light of different wavelengths scatters in tissue before it gets back out. Blood drawn from a vein arrives in the tube dark red and stays that way.