Blood vessels are a network of tubular structures, responsible for transporting blood around the body, to the tissues and organs. Blood is carried away from the heart by arteries, and back to the heart via veins. Along with these, you get smaller blood vessels known as arterioles (an extension of an artery which leads to a capillary), capillaries (the smallest type of blood vessel which allows for the passing of nutrients, dissolved gases etc.) and venules (an extension of a vein which connects to a capillary). Deoxygenated blood is carried to the lungs by veins, where it undergoes oxidation, this blood is then transported around the body by arteries, depositing oxygen to cells.