1 Blood returning from all parts of the body enters the right atrium.
2 From the right atrium blood passes through the tricuspid valve into the right ventricle.
3 After that it passes through the pulmonary artery to the lungs.
4 Here the blood gives up the waste carbon dioxide and takes in fresh oxygen.
5 Through the pulmonary veins blood returns to the left atrium.
6 Oxygen from the blood passes through the capillaries to the body cells and carbon dioxide and waste pass to the blood.
7 The capillaries unite to form veins which carry the blood and waste carbon dioxide back to the right atrium.
8 The circulation runs continuously.