Blood circulation in the human body is a continuous process facilitated by the heart, blood vessels (arteries, veins, capillaries), and blood. Oxygen-rich blood from the lungs enters the left atrium of the heart, then goes to the left ventricle, which pumps it into the aorta, the main artery. Arteries carry this oxygenated blood to all body parts. In capillaries, oxygen and nutrients are exchanged with tissues, and carbon dioxide and waste products are picked up. Deoxygenated blood then collects in veins and returns to the right atrium of the heart, moves to the right ventricle, which pumps it to the lungs for oxygenation, completing the circuit.