The tunica externa is generally the thickest layer in veins. This layer is made up of connective tissue and helps to anchor the vein to surrounding tissues. In some larger arteries, the tunica media may be thicker than the tunica externa, but in veins, the tunica externa is typically the dominant layer.
In contrast, the tunica media, which is primarily composed of smooth muscle, is typically the thickest layer in arteries. This is because arteries need to withstand higher pressure from the blood being pumped from the heart.
In summary, while both arteries and veins have three layers (tunica intima, tunica media, and tunica externa), the thickness of each layer differs between the two types of blood vessels. The tunica externa is thicker in veins, while the tunica media is thicker in arteries.
