Which part of the circulatory system carries deoxygenated blood?

Veins are responsible for carrying deoxygenated blood back to the heart. In the human circulatory system, after oxygen has been delivered to the tissues, the blood has a lower oxygen concentration and a higher concentration of carbon dioxide, making it deoxygenated. This blood travels through the veins, which are equipped with valves to ensure the one-way flow towards the heart.

Unlike arteries, which carry oxygenated blood away from the heart to the body, veins serve the critical function of returning deoxygenated blood to the heart for reoxygenation in the lungs. Capillaries, on the other hand, are the microscopic vessels where the exchange of oxygen and carbon dioxide occurs, but they do not have a distinctive role in transporting deoxygenated blood specifically. Venules are small vessels that collect blood from capillaries and lead to veins; while they do carry deoxygenated blood, their role is more of a transition rather than being the main carriers of deoxygenated blood. Thus, veins are the primary vessels for returning deoxygenated blood to the heart.