Arteries, Veins, Capillaries

Arteries:

any of the muscular-walled tubes forming part of the circulation system by which blood (mainly that which has been oxygenated) is conveyed from the heart to all parts of the body

Veins:

any of the tubes forming part of the blood circulation system of the body, carrying mainly oxygen-depleted blood towards the heart.

Capillaries:

any of the fine branching blood vessels that form a network between the arterioles and venules.