The Heart

The heart is an organ that mainly consists of cardiac muscle tissue, which allows it to contract and relax. The role of the heart is to pump blood all around the body and through the lungs.

It is located in the chest (or thoracic) cavity and just to the left of the centre of a human’s chest. Despite working all the time, the heart never gets tired.

The Heart Structure

Let’s look at a simplified diagram of the heart.

The heart has four chambers, two atria and two ventricles. At the top of the heart, we find the left atrium and the right atrium, and at the bottom, we find the left ventricle and the right ventricle. The atria and ventricles are separated by valves.

  • Heart diagrams are typically drawn as if you are looking at the person, so it appears to be back to front.
Heart ChamberProcesses in the chamber
Right atriumThe right atrium receives deoxygenated blood from the body, and then contracts, forcing the blood into the right ventricle.
Right ventricleThe right ventricle contracts, pumping blood into the pulmonary artery, which carries the blood to the lungs so it can be oxygenated.
Left atriumThe left atrium receives oxygenated blood from the lungs and then contracts, forcing the blood into the left ventricle.
Left ventricleThe left ventricle contracts, pumping blood into the aorta, which carries the blood around the whole body.

Thickness of the chamber walls

In the heart, the ventricles have thicker walls than the atria. This is because the ventricles pump blood around the body, so they generate greater pressure. Whereas, the atria only need to pump blood into the ventricles.

Also, the left ventricle has a thicker wall than the right ventricle. This is because the left ventricle is required to pump blood at high pressure around the whole body. Whereas the right ventricle only needs to pump blood to the lungs, which is a much shorter distance, so it generates lower pressure.

  • The two sides of the heart are separated by the septum

Heart valves

Valves in the heart stop the blood from flowing backwards, which creates a one-way flow.

  • Atrioventricular valves separate the atria from the ventricles
  • Semilunar valves are located at the end of the pulmonary artery and the aorta, at the point at which they intersect with the left and right ventricles.