(I lost the source for this image. If it is yours, contact me and I'll credit you.)
We maximize nutrient exchange by increasing the surface area for diffusion (lots of tiny vessels instead of one big vessel) and slowing down the blood once it gets to the capillaries so it spends more time in the tissues. The professor for the class originally explained nutrient exchange as someone trying to pick candy off of a conveyor belt. We want the conveyor belt to move slowly so we can maximize the number of candies we can grab off of it before they pass us by. I thought this was a clever way to explain the concept, because my mind immediately went to the classic chocolate factory scene in I Love Lucy.
However... in the office hours and at the review session it became increasingly apparent to my co-TA and I that many of our students weren't getting the reference. And since they didn't get the reference, they didn't really understand the analogy. We told them to look it up on Youtube when they got home, but one student had his laptop in the room so he looked it up immediately. Other students watched it over his shoulder... began to laugh... and I could see the click happen. Suddenly they got it.
Seriously, what kind of person has never seen the chocolate factory episode of I Love Lucy? I didn't think there was a generation gap between my students and I, but now I'm starting to wonder.