Circulation means to recycle, that is, to move round and round. There are many circulations in our bodies.

The blood is the easiest one to understand. It begins with the heart. The heart is a large muscle that pumps blood around the body. But it is actually two pumps in one. Part of the heart pumps used blood into the lungs, where it soaks up oxygen (and turns from a dark mauve/blue colour to bright red). The other part of the heart then pumps this blood through the rest of the body, where the oxygen, and other materials in the blood, are gradually released to all the parts of the body that need them. After a while the oxygen is partly used up and the blood begins to turn mauve again. It then moves through the veins and back to the heart, where it is recycled into the lungs.