Return to main circulatory system page The one-way circulatory
system carries blood to all parts of your body. This process of
blood flow within your body is called circulation. Arteries
carry oxygen-rich blood away from your heart, and veins carry
oxygen-poor blood back to your heart. In pulmonary circulation,
though, the roles are switched. It is the pulmonary artery that
brings oxygen-poor blood into your lungs and the pulmonary vein
that brings oxygen-rich blood back to your heart. In the
diagram, the vessels that carry oxygen-rich blood are colored
red, and the vessels that carry oxygen-poor blood are colored
blue. Updated August 2012