Small muscular artery. Light micrograph of a cross-section through a small muscular artery and surrounding tissue. These small blood vessels link the larger arteries and the arterioles, controlling blood flow (red blood cells at centre) and blood pressure by contraction and relaxation. Contraction is regulated by the smooth muscle of the tunica media layer. The prominent wavy elastic layer next to the vessel lumen is the internal elastic lamina which restrains expansion of the vessel lumen. Other elastic laminae (black wavy lines) are also seen, along with the tunica adventitia layer (green-blue). Magnification: x120 when printed at 10 centimetres across.