Arteries transition into arterioles, then capillaries with single-cell-thick walls for nutrient and oxygen exchange.

“But then those arteries are going to transition into smaller diameter tubes that we call the "arterioles," and then eventually, as those arterioles approach the tissues they need to deliver all that stuff, all those goodies within the blood, those arterioles are going to transition and start branching into what are called "capillaries." Most of you have probably heard of capillaries. Capillaries have a very, very thin wall, just one cell thick, which allows things within the blood, like oxygen, amino acids, and other things that the cells and the tissues of your body need to actually get out into those tissues.”