there are brain veins!! anywhere fresh blood is supplied by artery there needs to be veins to take it all back to the heart and lungs to be reoxygenated. <br>in the body there are few cases of having only veins or only arteries in a certain system. one of them is how the kidney is supplied with the blood it filters. since you define arteries vs veins by which way their flow is moving relative to the heart you get the quirk that a supply of blood to the kidney, input and output, does not change its direction relative to the heart as it supplies blood to the kidneys to be filtered. so it's artery in and artery out, no veins and no capillaries beyond the glomerulus (a bunch of capillaries practically, but not doing much gas exchange) for which the two arteries in question supply both input and output. normally, like in a muscle or your lungs, you have an artery on the supply end, capillaries exchanging supply for waste, and a vein taking away the waste. In the glomerulus there's oxygenated arterial blood flowing in and out with some percentage filtered into the kidney while the rest flows on without changing direction relative to the heart.<br>really at the small scale that this is happening on the arteries are arterioles, a smaller form of an artery that's used for bridging the gap between arteries and the capillaries they supply. it's still arteriole in and arteriole out, though.