Why must the vasa vasorum of a large artery run in the outer layers of the wall rather than close to the lumen?

1. Large vessel walls are too thick for luminal blood to nourish every cell by diffusion. 2. The vasa vasorum, literally vessels of the vessel, supply those wall cells. 3. Pressure inside an artery is high, so a vasa vasorum close to the lumen would be squashed shut and no exchange could occur. 4. The lower pressure inside a vein lets its vasa vasorum sit much closer to the lumen. 5. Nerves do run in arterial walls as the nervi vasorum, so option A is false. 6. Endothelium does not block all inward movement, since the basement membrane beneath it is permeable. 7. Lumen width is irrelevant here, because the vasa vasorum branch from outside the vessel. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 20 "The Cardiovascular System: Blood Vessels and Circulation", section 20.1 Structure and Function of Blood Vessels_