Light micrograph of an artery showing transition from elastic (upper) to muscular type (lower). The wall of elastic arteries show multiple layers of elastin (purple) in the tunica media whereas in muscular arteries smooth muscle cells predominate in the tunica media, Elastic fibers recoil after the artery is stretched by pulsatile blood pumping. Muscular arteries regulate vessel diameter and control blood pressure and blood flow to organs and tissues. Paraffin section, Verhoeff's/Masson trichrome stain. Magnification x100 printed at 10cm wide.