which type of blood vessel has the thickest walls?

The type of blood vessel with the thickest walls is the artery. Arteries have thick walls composed of three layers: the tunica intima (thin inner layer), the tunica media (the thickest middle layer made mostly of smooth muscle and elastic fibers), and the tunica externa (outer layer). The thick tunica media allows arteries to withstand and regulate the high pressure of blood pumped from the heart. This is in contrast to veins and capillaries, which have thinner walls due to lower blood pressure in those vessels.