Pulmonary circulation

In the pulmonary circulation, blood goes from the heart to the lungs, where it releases carbon dioxide and takes up oxygen, then returns to the heart. In the systemic circulation, blood goes from the heart to body tissues, where oxygen is delivered, then returns. Passing through the heart between the two loops lets blood be pumped again at the higher pressure needed to travel around the whole body.

The pulmonary circulation links the heart and lungs. Deoxygenated blood returns from the body to the right side of the heart through the vena cava. It is pumped through the pulmonary artery to capillaries surrounding the lungs' gaseous exchange surfaces.