Answer:
"An artery carries oxygenated blood away from the heart to all parts of the body while veins carry deoxygenated blood back to the heart."
That's not always true. In the pulmonary system, the pulmonary artery carries deoxygenated blood to the lungs and the pulmonary veins carry oxygenated blood back into the left atrium. It is better to say that arteries always bring blood out of the heart and veins bring blood into the heart.
Histologically, veins have a large, floppy irregular lumen and a thinner wall. They also contain valves to prevent backflow when blood is being taken back up to the heart.
Arteries usually have a round lumen and thick walls, but no valves.
Veins pump purified blood from the heart to the body.
Arteries pump unpurified blood to the heart from the body.