Question

Blood in the human body circulates twice for making one complete round through the body. Explain.

Answer 1

The circulation of blood through the human heart takes place twice making one complete round through the body. This is called double circulation. The impure blood (deoxygenated blood) is collected from different body organs through two major veins (vena cava). The two veins empty blood into the right auricle. From here, it enters the right ventricle and is carried to lungs by pulmonary artery. Exchange of gases takes place in the lungs. Pulmonary vein then carries the pure (oxygenated) blood to the left auricle. From here, it enters the left ventricle and is then carried by an artery called aorta to all parts of the body.

Double circulation can be summarised as:

Circulation of blood between the heart and the lungs is called pulmonary circulation.
In this, the blood flows as follows:
Right ventricle → lungs → left auricle (through pulmonary veins)

Circulation of blood between the heart and body organs (except lung) is called systemic (body) circulation.
Blood flows as following:
Left ventricle → body organs → right auricle (through vena cava)