Why double circulation is necessary in human beings?
Answers
Double circulation describes the fact that our oxygenated and deoxygenated blood is kept separate in our hearts. In fish (two-chambered heart) and amphibians (three-chambered heart), the oxygenated and deoxygenated blood is allowed to mix in the ventricles, in mammals and birds (four-chambered heart), the oxygenated and deoxygenated blood is kept separate. Fish and amphibians are cold-blooded, meaning that they conform to the temperature of their environment. Mammals and birds are warm blooded. They maintain a constant internal temperature, despite the environment. Maintaining a constant internal temperature allows mammals and birds to carry-out body processes more efficiently, but it requires more energy. Without double circulation, the body tissues would not receive enough oxygen to maintain a constant temperature, and would die.
In response to the above answer, some amphibians have lungs. Having lungs does not mean an organism has a double circulatory system.
In mammals and birds the blood goes through the heart twice during each cycle. This is known as double circulation.
Deoxygenated blood which enters right auricle and then it enters the right ventricle from where it is pumped to lungs for oxygenation. From lungs after oxygenation it comes to left auricle and then enters left ventricle from where it is pumped to various parts of body.
Such system of circulation does not allow mixing of oxygenated and deoxygenated blood which allows efficient supply of oxygen to the body.