Blood vessels, light micrograph. An arteriole and venule are shown. The arteriole (upper left) has a thick wall of smooth muscle layers, the tunica media, and elastic fibres (dark blue). Facing the vessel lumen is the convoluted internal elastic lamina. The venule is a larger vessel with thin walls also comprised of smooth muscle and elastin. Red blood cells are suspended in blood plasma (green). Paraffin section, Gomori trichrome stain. Magnification: x280 when width printed at 10cm.