Q. 11 Describe double circulation of blood in human beings. Why is it necessary?
Deoxygenated blood rich in carbon dioxide and deficient in oxygen reaches the heart through a networl of veins and enters the heart through the vena cava and is brought into the right atrium. From the right atrium the deoxygenated blood goes to the right ventricle from where it is pumped to the lungs through pulmonary artery where carbon dioxide is released into the environment and oxygen is absorbed in the blood. From the lungs the oxygenated blood enters the left atrium through the pulmonary vein. From the left atrium the blood enters the left ventricle from where it is pumped to all parts of the body to facilitate the supply of oxygen.
This double circulation in human beings helps maintain high oxygen levels in blood which facilitates sufficien aerobic respiration for the generation of sufficient heat to maintain the body temperature.