T H E   G R E E N H O U S E

Human Circulation
 &nbsp- Blood Vessels
 &nbsp- The Heart
 &nbsp- Heart Applet
 &nbsp- Circulation Problems
 &nbsp- Circulation Test
 &nbsp- Links

The Heart

The heart is the organ which pumps blood around your entire body. It pumps blood to the body cells, and also pumps blood to the lungs to get reoxiginated. The pumping is caused the systole(contraction) and diastole(relaxation) of the heart. The diagram will help with the description of how the heart works.

1 - The blood returns through the venae cavae and enters the right atrium. This increases the pressure, and forces the tricuspid(there are 3 flaps) valves open, allowing the blood to flow into the right ventricle.

2 - When both the ventricle and atrium are full of blood, the atrium suddenly contracts. This pushes all the blood into the ventricle. This ventricle has powerful muscular walls, which contract more powerfully, forcing the blood up the pulmantory artery.

3 - The tricuspid valves prevent the blood being pushed back into the atrium. Strong cords called tendinous cords prevent the valves from being turned inside out. They run on the underside of each flap and are anchored in the ventricle wall. More valves in the pulmanory artery, called semilunar valves prevent blood falling back into the ventricle.

4 - The pulmanory arties takes the blood to the lungs. There is exchanges waste like CO₂ for fresh oxygen. The reoxiginated blood then returns to the heart via the pulmanory vein, to be pumped around the body.

5 - It enters the left artium and goes into the left ventricle. The flow of blood occurs in the same manner as it did in the right side, except thats there are bicuspid(2 flaps) instead of tricuspid valves. It enters the main artery called the aorta, and flows to the rest of the body.

During systole, the right side contracts first, and then the left side. This occurs very quickly, so appears to happen simulaneously. So as deoxyginated blood is being pumped from the right ventricle to the lungs, oxyginated blood is being pumped from the left ventricle to the aorta.

Then distole occurs(relaxation). This is when the heart refulls with blood again. This complete cycle is called the cardiac cycle, and is controlled by electrical impulses in the heart wall. The beating sound is caused by the blood hitting against the valves as they close.

The reason there are 2 chambers - the left and right side, is to separate the deoxygenated from the oxygenated blood. If they were to mix, the process of oxygenation would be very ineffective, and the blood would have less oxygen and more waste. Babies have a tiny hole in their heart, joining the two chambers. This isn't used and by the time of birth is usually sealed. Sometimes children are born with this hole and it needs to be closed by an operation. Since the quantity of oxygen and CO₂ in the blood is incorrect, the child will not be able to run well, and will get tired quickly.