Answer
It is the process by which the blood passes the heart two times in the complete cycle.
The two circulations involved are:
- Pulmonary circulation
- Systemic circulation
In Pulmonary circulation, the blood is circulated between heart and lungs.
In systemic circulation, the blood is circulated between heart and organs and cells of the body.
The heart receives deoxygenated blood from different parts of the body, and it pumps this blood to the lungs. The oxygenated blood from the lungs returns to the heart, which is pumped again into different parts of the body by the heart. Thus, the blood passes twice through the heart making one complete round through the body.It is necessary to prevent the mixing of oxygenated and deoxygenated blood.