The role of the atria and ventricles in the circulatory system is crucial for proper blood circulation throughout the body. The atria are the upper chambers that receive blood returning to the heart, while the ventricles are the lower chambers responsible for pumping blood out of the heart. The right atrium receives deoxygenated blood from the body, sending it to the right ventricle, which pumps it to the lungs for oxygenation. Meanwhile, the left atrium receives oxygenated blood from the lungs and directs it to the left ventricle, which supplies the rest of the body, ensuring efficient circulation.