The second order systemic output blood is selectively deoxygenated by the needs of the peripheral organs, returning once again to the heart.It is referred to as a closed circulatory system because blood usually travells in the body through blood vessels.
The second order systemic output blood is selectively deoxygenated by the needs of the peripheral organs, returning once again to the heart where it returns back to the lungs to become oxygenated again. A double-loop system is also a closed circulatory system because blood usually travells in the body through distinct blood vessels.