Final answer:
The blood vessel described is a vein, which has a large lumen and relatively thin walls due to less smooth muscle and elastin, allowing it to conduct blood toward the heart under lower pressure.
Step-by-step explanation:
The vessel type described by the student, which includes a large lumen with an average diameter of 5.0 mm and thin walls averaging 0.5 mm, but has relatively little smooth muscle or elastin in the tunica media, is indicative of a vein.
Veins are blood vessels that conduct blood toward the heart and are part of the lower-pressure venous system. Unlike arteries, which have a thick tunica media for controlling blood pressure and flow, veins have a thinner tunica media. A thick tunica media and a large amount of elastic fibers are characteristics of arteries, which allow them to withstand the high pressure of blood pumped from the heart. However, further from the heart, as the blood pressure decreases, the necessity for these features lessens, and the vessel walls of veins become thinner.