The three (3) main differences both veins and arteries are:
1. Arteries carry oxygenated-rich blood, while veins carry deoxygenated-rich blood.
2. Pulmonary arteries carry deoxygenated blood from the heart to the lungs, while pulmonary veins carry oxygenated blood from the lungs to the heart.
3. The blood flowing in the arteries is under high-pressure, while the veins are under low-pressure.