#Science - Socratic.org Sunday throwback - Why are arteries thicker than veins?

As I've mentioned before, I used to be quite active on Socratic.org, a free-to-use question and answer website. However, the powers that be at that site decided to turn it into read-only (it actually went read-only this past week), and so I highlight past questions and answers that seemed to catch people's attention. Today's question is:

Question

Why are arteries thicker than veins?

Answer

To withstand the high pressure of blood coming from the heart.

Analysis

The "heart" of the circulatory system is the heart. It pumps blood through arteries (starting with the biggest one of them all, the aorta). The blood runs through smaller and smaller arteries until it gets to a capillary, where the blood drops off oxygen and nutrients to cells and receives carbon dioxide from the cells. 

Also at the level of the capillaries, a bit of plasma "leaks" into the space between cells, becoming interstitial fluid (which is recaptured in a main vein just above the heart through the lymphatic system).

On the return trip, blood flows through veins and ends up back at the heart (there is activity with the lungs but we'll ignore that for now).

The whole system is under pressure - a high pressure on the outflow from the heart and a lower pressure on the inflow. Because of that high pressure on the outflow from the heart, the walls of the arteries need to be thicker.  Veins, which are under far less pressure, have thinner walls. In order to help the blood flow back to the heart, veins have "check valves" - blood can flow through towards the heart but can't flow backwards away from it.

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As always, questions and comments welcome!