ARTERIES VS VEINS

Arteries carry oxygenated blood away from the heart, while the veins return deoxygenated blood to the heart so that it will be pumped by the heart to the lungs and become oxygenated again. Veins are more superficial and thinner than arteries, which lie deeper inside your muscles and are more extensive in structure. These two blood vessels greatly vary from each other, but there are minimal similarities that sometimes confuse people. These are: both of them are part of the circulatory system; they both transport blood; they are made up of different layers to aid the flow of blood with them; and both of them prohibit backflow of blood.
 
So, given that arteries carry oxygenated blood, it also means that pressure is higher; thus, there is a need for a thicker membrane and a larger circumference to cater to such pressure inside the artery. On the other hand, veins are thinner as they only transport deoxygenated blood, where pressure is much lower compared to arteries. Although these two have the same layer, namely tunica intima, tunica media, and tunica adventitia, these layers only differ in thickness to cater to the blood vessel function.
 
There are different types of veins: pulmonary and systemic. Pulmonary veins carry deoxygenated blood to the heart, while systemic veins carry deoxygenated blood from other body parts. All veins consist of valves because the pressure is lower and the blood flowing within them is deoxygenated; thus, there is a need for a valve to prevent backflow. While arteries do not have any valves, pressure is the one that is already responsible for preventing the backflow of blood.

References:
https://www.webmd.com/heart/difference-between-arteries-veins-capillaries

Veins & Arteries Similarities And Differences

https://training.seer.cancer.gov/anatomy/cardiovascular/blood/classification.html#:~:text=Although%20all%20the%20layers%20are,pressure%20than%20in%20the%20arteries.
https://www.osmosis.org/learn/Artery_and_vein_histology
https://www.healthline.com/health/venous-system#symptoms-of-a-venous-condition