My biology textbook says that arteries have a small lumen relative to the thickness of their walls. I understand why they need thick walls, to withstand high pressure and stretch etc. But when explaining the reason for the "small" lumen, it says that it is to "maintain the high pressure". I'm not quite sure what this means.
What would happen if the lumen was larger? Wouldn't a small lumen create resistance to blood flow? And what exactly is blood pressure? Also, it says that veins have a "large" lumen. Why is this so? I think my confusion is a lack of understanding of what blood pressure really means. Why does velocity not seem to make a difference?