Explanation

Heart has four chambers: right side pumps deoxygenated blood to lungs, left side pumps oxygenated blood to body. Valves prevent backflow.

Blood vessels: arteries (thick walls, carry blood away from heart), veins (thinner walls, valves, carry blood toward heart), capillaries (thin walls for exchange).

Double circulation: blood passes through heart twice per circuit – once for pulmonary (lung) circulation, once for systemic (body) circulation. This maintains high pressure for efficient delivery.