Blood vessels. Light micrograph of a section through tissue showing an elastic artery and two veins. Surrounding the artery and vein are layers of smooth muscle (red), and fibrous connective tissue. Red blood cells fill the lumens of all three vessels. Arteries carry blood away from the heart, while veins carry blood back to the heart from the rest of the body. Magnification: x13 when printed at 10 centimetres wide.