And in arteries, the tunica media is a thick layer. So arteries contain a thick layer of smooth muscle and we'll see why that's important in just a moment. Now the outer layer is our tunica extrema and this basically contains our collagen fibers. And collagen fibers give the blood vessels its strength. And these collagen fibers also anchor the blood vessel along the organs found surrounding our blood vessel. Now what are some properties of our arteries and how exactly does blood actually flow through the arteries?