7.2 The human heart

7.2.5 Heart blood flow

Coronary circulation provides blood supply to the heart. The blood flow is in one direction, from the atria to the ventricles, and it flows out through the aorta and the pulmonary artery. The tricuspid, bicuspid, aortic, and pulmonary valves prevent the blood from flowing backwards.

The heart has a double pump action. The right side of the heart collects de-oxygenated blood. It flows via the superior and inferior venae cavae from the body into the right atrium, and it is then pumped, via the right ventricle, into the lungs (pulmonary circulation). Here carbon dioxide can be exchanged for oxygen, which happens through the passive process of diffusion. The left side of the heart collects the oxygenated blood from the lungs into the left atrium and from there to the left ventricle which pumps the blood out to the body via the aorta.

The atria and ventricle walls are muscular, but the lower ventricles are thicker and stronger than the upper atria. Also, the wall surrounding the left ventricle is thicker than that surrounding the right ventricle. This is because a higher force is needed to pump the blood circulation. The atria primarily facilitate circulation by allowing uninterrupted venous flow to the heart. This prevents the inertia of interrupted venous flow which would otherwise occur.