Double circulation in human beings refers to the two separate circuits through which blood flows in the body. It is a highly efficient system that ensures oxygenated blood is supplied to all organs and tissues while deoxygenated blood is returned to the lungs for oxygenation. The two circuits are the pulmonary circulation and systemic circulation.

Pulmonary Circulation:
The pulmonary circulation is responsible for oxygenating the blood. It begins when deoxygenated blood from the body enters the right atrium of the heart through the superior and inferior vena cava. From the right atrium, the blood is pumped into the right ventricle and then to the lungs through the pulmonary artery. In the lungs, carbon dioxide is released, and oxygen is picked up. Oxygenated blood then returns to the heart through the pulmonary veins and enters the left atrium.

Systemic Circulation:
The systemic circulation delivers oxygenated blood to all parts of the body. From the left atrium, oxygenated blood is pumped into the left ventricle. The left ventricle is the strongest chamber and it contracts forcefully to pump blood into the aorta, the largest artery in the body. The aorta branches into smaller arteries, which further divide into arterioles and then capillaries. Capillaries are tiny blood vessels that allow for the exchange of oxygen, nutrients, and waste products with body tissues. Deoxygenated blood, carrying waste products like carbon dioxide, enters venules, which merge to form veins. These veins progressively merge into larger veins and finally into the superior and inferior vena cava, which return the deoxygenated blood to the right atrium, completing the circuit.

Benefits of Double Circulation:
1. Efficient Oxygenation: Double circulation ensures efficient oxygenation of blood as it passes through the lungs, allowing for a high concentration of oxygen to be delivered to the body's tissues.
2. Separation of Oxygenated and Deoxygenated Blood: The separation of oxygenated and deoxygenated blood prevents mixing, ensuring that oxygen-rich blood is delivered to the body's organs and tissues while deoxygenated blood is returned to the lungs for oxygenation.
3. Increased Blood Flow: The double circulation system allows for a higher volume of blood flow, which ensures that the body's cells receive an adequate supply of oxygen and nutrients.
4. Regulation of Blood Pressure: The separate pulmonary and systemic circuits help regulate blood pressure by dividing the workload between the right and left sides of the heart.

In conclusion, double circulation in human beings is a highly efficient system that ensures oxygenated blood is delivered to all organs and tissues while deoxygenated blood is returned to the lungs for oxygenation. It involves the pulmonary circulation, which oxygenates blood in the lungs, and the systemic circulation, which delivers oxygenated blood to the body's tissues. This system provides numerous benefits, including efficient oxygenation, separation of oxygenated and deoxygenated blood, increased blood flow, and regulation of blood pressure.