If all a person's blood vessels - arteries, veins and capillaries - were laid end to end, they would be 100,000 kilometers long. Arteries bring oxygenated blood from the heart to the body's organs and tissues. Veins bring oxygen-depleted blood to the heart. The tiny capillaries link the arteries and veins.
They are where the exchange of fluids, gases, waste and nutrients between the blood and the body's tissues takes place.