There are two types of blood vessels in the circulatory system of the body: arteries that carry oxygenated blood from the heart to various parts of the body and veins that carry blood towards the heart for purification.hey are tiny branches of arteries that lead to capillaries and help maintain the pressure and blood flow in the body. Venous valves prevent blood from flowing in the opposite direction. Connective tissues make up the outermost layer of a vein which is also known as-tunica adventitia or tunica externa.