Arteries:
Arteries carry oxygenated blood away from the heart and to the rest of the body. The aorta is the largest artery in the body and it branches off into smaller arteries that supply blood to different organs and tissues. Arteries have thick, muscular walls that help to pump blood against the pressure of the bloodstream.
Veins:
Veins carry deoxygenated blood back to the heart. Veins have thinner walls than arteries and they contain valves that help to prevent blood from flowing backward. The largest vein in the body is the vena cava, which carries blood from the lower body back to the heart.
Capillaries:
Capillaries are the smallest blood vessels in the body. They connect arteries to veins and they allow for the exchange of oxygen, carbon dioxide, and other nutrients between the blood and the surrounding tissues. Capillaries have very thin walls that allow for the diffusion of substances between the blood and the tissues.