Biology · Body Fluids and Circulation · NEET
Twice. In one complete round of the body, blood enters the heart, goes to the lungs, comes back to the heart, and only then is sent to the body. Because it visits the heart on two separate occasions, it is called DOUBLE circulation. Fishes have single circulation (blood passes the heart only once per round).
The RIGHT ventricle starts pulmonary circulation: it pumps deoxygenated blood to the lungs. The LEFT ventricle starts systemic circulation: it pumps oxygenated blood to the whole body. NCERT states this directly, so keep right = lungs, left = body fixed in your memory.
A vessel is named by DIRECTION, not by the type of blood. Any vessel carrying blood AWAY from the heart is an artery, and any vessel bringing blood TO the heart is a vein. So the pulmonary artery (heart to lungs) carries deoxygenated blood, and the pulmonary vein (lungs to heart) carries oxygenated blood. These two are the famous exceptions NEET loves.
Pulmonary circulation: right ventricle to pulmonary artery to lungs (blood gets oxygenated) to pulmonary veins to left atrium. Systemic circulation: left ventricle to aorta to all body tissues (blood loses oxygen) to veins (vena cava) to right atrium. Pulmonary handles gas exchange; systemic delivers oxygen and nutrients to the body.
Double circulation keeps oxygenated blood and deoxygenated blood completely separate, so tissues always receive fully oxygen-rich blood. It also allows higher blood pressure for the body path (systemic) and gentler pressure for the delicate lungs (pulmonary). This efficient supply supports the high energy needs of warm-blooded mammals.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a system where blood passes through the heart two times to complete one full round of the body. First it goes to the lungs (pulmonary), then to the body (systemic).
It begins at the right ventricle (pumping deoxygenated blood to the lungs) and ends at the left atrium (receiving oxygenated blood from the lungs).
It begins at the left ventricle (pumping oxygenated blood into the aorta to the body) and ends at the right atrium (receiving deoxygenated blood from the body through the vena cava).
It keeps oxygenated and deoxygenated blood from mixing, ensures body tissues get fully oxygenated blood, and lets the two paths run at different pressures suited to the body and the lungs.
Birds and mammals (including humans) have a 4-chambered heart with complete double circulation. Amphibians and most reptiles have incomplete double circulation because of a single or partly divided ventricle.
