What describes the main difference between veins and arteries in circulatory system?

Veins and arteries are the two types of blood vessels that make up the circulatory system. Arteries carry oxygen-rich blood away from the heart to the rest of the body, while veins carry oxygen-depleted blood back to the heart.

The main difference between veins and arteries is the presence of valves in veins. Valves are one-way flaps that prevent blood from flowing backward. This is important because veins are often located below the heart, and without valves, blood would pool in the veins and not be able to return to the heart.

Arteries do not have valves because blood is pumped through them by the contraction of the heart. The high pressure of the blood in arteries keeps it moving forward, even against gravity.

In addition to valves, veins also have thinner walls than arteries. This is because veins do not need to withstand as much pressure as arteries. The high pressure in arteries is necessary to pump blood throughout the body, but veins do not need to generate any pressure.

Finally, veins are often located closer to the surface of the skin than arteries. This is why veins are often visible on the skin, while arteries are not.