Final answer:
The lumen of an arteriole averages 30 micrometers or less in diameter. The wall thickness of an arteriole is determined by the three tunics: tunica intima, tunica media, and tunica externa.
Step-by-step explanation:
An arteriole has a lumen averaging 30 micrometers or less in diameter. The wall thickness of an arteriole is determined by the three tunics called the tunica intima, tunica media, and tunica externa. These tunics are composed of endothelial lining, smooth muscle cells, and connective tissue, respectively.