Right now, a fist-sized pump in your chest is pushing blood through pipes all over your body — about once a second, your whole life. Today you'll learn how, then you will predict where the blood goes next.
Before we start — put a hand on your chest — that steady thump you can feel is today's whole lesson, already at work.
The heart is a muscle that pumps. The blood is the delivery liquid. The blood vessels are the pipes that carry blood to every corner of your body and back.
Blood carries oxygen (picked up in the lungs) and food to every cell, and carries waste away. Blood full of oxygen is drawn red; once the oxygen is dropped off it's drawn blue.
Blood doesn't do one big circle. It does two loops through the heart: a short loop to the lungs to pick up oxygen, then a long loop out to the body to drop it off — and back to the heart each time.