Double Circulatory System

The human circulatory system has three key components: blood vessels, blood and the heart. It is called a double circulatory system because blood passes through the heart twice per circuit.

The right pump sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart.

The left pump sends the newly oxygenated blood around the body. By the time this blood returns to the heart, it has returned to a deoxygenated state.

Circulatory System Diagram

Blood Passes Through The Heart Twice Per Circuit

Blood enters the heart

Deoxygenated blood from the body enters into the right atrium of the heart.

Blood pumped to lungs

This deoxygenated blood is pumped out of the heart and towards the lungs by the right ventricle.

Lungs oxygenate the blood

At the lungs, the deoxygenated blood exchanges carbon dioxide for oxygen. This is how it becomes oxygenated (contains oxygen).

Blood returns to the heart

Oxygenated blood returns to the left atrium of the heart.

Blood pumped to the body

This oxygenated blood is pumped out of the heart and to the body by the left ventricle.

Blood returns to the heart

The oxygenated blood gives its oxygen to body cells in exchange for carbon dioxide. The blood becomes deoxygenated and returns to the heart.