Q.Explain in brief double circulation (human).

Human (double) circulation routes blood through the heart twice per cycle — once to the lungs and back (pulmonary circulation) and once to the rest of the body and back (systemic circulation) — which keeps oxygenated and deoxygenated blood from mixing and makes oxygen delivery far more efficient.

Double Circulation in Humans

The human heart is four-chambered (two atria, two ventricles), and blood completes two distinct circuits, both passing through the heart, in a single full circulation — hence "double circulation."

1. Pulmonary circulation (right side of heart to lungs and back): deoxygenated blood from all body tissues collects in the right atrium (via the superior and inferior venae cavae), passes to the right ventricle, and is pumped through the pulmonary artery to the lungs. In the lungs, carbon dioxide is released and oxygen is absorbed, so the blood becomes oxygenated. This oxygenated blood returns via the pulmonary veins to the left atrium of the heart.
2. Systemic circulation (left side of heart to body and back): oxygenated blood from the left atrium passes to the left ventricle, which pumps it through the aorta to all body tissues, supplying them with oxygen and nutrients. At the tissues, oxygen is used up and carbon dioxide/wastes are picked up, so the blood becomes deoxygenated, and it returns via the venae cavae to the right atrium, completing the circuit. …