Describe double circulation in human beings. why is it necessary?

Double circulation occurs in humans. It refers to the passage of same blood twice
through the heart. The right side receives deoxygenated blood whereas the left chambers of the heart pump oxygenated blood. There is no intermixing of oxygenated and deoxygenated blood. The oxygenated blood from lungs comes to left auricle through pulmonary veins. Simultaneously, the deoxygenated blood comes to right auricle through two large veins Contraction of ventricles results in transfer of blood from them into lungs and various body parts. Precisely left ventricle on contraction sends oxygenated blood to body through the largest
artery Aorta. While the right ventricle pumps the blood into lungs and for oxygenation through pulmonary artery. The separation of the right side and left side of the heart is useful so as to prevent oxygenated and deoxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body. This is useful in animals that have high energy needs, such as birds and mammals, Which constantly use the energy to maintain their body temperature.