Veins and arteries are both part of the circulatory system and they are responsible for transporting blood throughout the body. The main difference between them is the direction of blood flow. Arteries carry oxygenated blood away from the heart, while veins carry deoxygenated blood back to the heart. Another difference is that veins are usually closer to the skin and have thinner walls than arteries. This is because veins have to deal with lower blood pressure than arteries. Arteries are also surrounded by a thicker layer of connective tissue.