When the blood flows twice through the heart in each cardiac cycle (each course of . circulation) it is called double circulation. Deoxygenated blood from the body is brought to right atrium through great veins. From right atrium blood is sent to right ventricle and from here it is pumped to lungs for purification.
The oxygenated blood is carried to left atrium. From the left atrium blood moves to left ventricle. Left ventricle pumps this blood to all body parts through aorta. As blood flows twice through the heart in one complete cycle it is called double circulation.
Significance- It keeps the oxygenated and deoxygenated blood separated and does not allow their mixing. Such a separation allows a highly efficient supply of oxygen to all body cells. This is specially required in organisms having high metabolic rate. Birds and mamma1s, including human being are warm blooded animals. To keep their body temperature constant their energy requirements are ligh, so they need double circulation.
