Describe double circulation in human beings, Why is it necessary ?

Explanation

When blood flows twice through the heart before making one complete circulation is called double circulation. In double circulation, there are two pathways in which the blood flows. They are:
Long Systemic circulation: Systemic circulation carries oxygenated blood from the left ventriclesto the aorta for circulating into various parts of the body. Later, the deoxygenated blood - which is rich in carbon dioxide from various parts of the body is pumped back into the superior vena cava and then to the right auricle.
Short Pulmonary circulation: In the pulmonary circulation, the blood circulation starts from the right ventricle, where The pulmonary artery collects the blood and carries to lungs for oxygenation. Once after the purification process, the oxygenated blood is pumped back to the left auricle through the pulmonary vein which is carried to the left ventricles.