The heart

- Beep-blip-beep-ping? - Oh, hello. I'm.... just drawing something. A card. It's for Michael.

Drawing a heart is a way to say that you like someone. I think it's because you feel it in here, where the heart is, when you really like someone. Beep-blip-beep-beep? Is the heart for feeling things? No, not at all.

It's a pump, actually. That's right. The heart is a powerful pump that works around the clock your entire life. Oxygenated blood is pumped from the lungs into the body. The oxygen is used by the body's cells.

The blood, which is now deoxygenated, is then pumped back to the lungs. There it is reloaded with new oxygen from the air we breathe in. This is what the heart looks like close up. We cannot control the heart muscle by willpower. The contractions are controlled by electricity...

Every heartbeat is started by an electric pulse that comes from a place inside the heart muscle. The heart is divided into two sections, with a wall in-between. Each section consists of two spaces: An atrium... and a ventricle. The blood first enters the atria and from there continues to the ventricles.

Between each atrium and each ventricle is a kind of vent, or valve. The valves are flaps of collagen. They open easily, but only one way. When the atria contract, the blood is pushed past the valves into the ventricles. When the ventricles contract, the valves' flaps are pushed flat, so that no blood can flow back into the atria.

There are also valves where the blood exits the ventricles. They kind of work the same way and keep the blood from flowing back into the ventricles. It's a bit like in a beach ball. When you blow air through the vent, the airstream pushes away a little flap. When you stop blowing the flap goes back, and the pressure from the air inside the ball keeps the flap in place.

This way, not much air leaks out while you insert the plug. The two sections of the heart work with separate parts of the circulatory system. We're going to take a closer look at one section at a time. The heart's right section works with the deoxygenated blood, that's going to the lungs to drop off carbon dioxide and get new oxygen. Through the superior vena cava comes blood from the head, throat, chest and arms.

Through the inferior vena cava comes blood from the legs, abdomen and pelvis. Both of the venae cavae go into the right atrium. From the right atrium the blood is pumped into the right ventricle, and from there out to the lungs, through the pulmonary artery. In the lungs, the blood releases carbon dioxide and receives new oxygen from the air we breathe in. Then the blood goes back to the heart, and now it's the left section that gets to work.

Via the pulmonary veins the blood enters the left atrium. From there, it is pumped to the left ventricle, and then it goes through the aorta, to the entire body! To pump blood through the entire body requires more force than pumping blood to the lungs. Therefore, the heart muscle is stronger and bigger around the left ventricle. All muscles need oxygen, which they get from the blood.

This of course applies to the heart muscle as well. So the heart has its own vessels, on the outside: coronary vessels. The coronary vessels shown red in the picture transport blood to the heart directly from the aorta. The blood flows as the heart rests between contractions. From the heart muscle, deoxygenated blood flows through the vessels shown blue in the picture.

The vessels go to the backside of the heart, into the right atrium, and from there the blood is pumped to the lungs. There we go! Be-beeeep! Oh! Eh...

Thanks! How sweet of you!