Coronary artery. Light micrograph of a cross-section of a normal human coronary artery, which supplies blood to the heart. The micrograph shows the arterial wall as a circle of pink-stained tissue, surrounding the lumen, or space, at centre. The lumen contains red blood cells. Arterial walls are made to withstand the pressure exerted by the pumping action of the heart. The walls (pink) consist of elastic fibres and smooth muscle, the latter of which is under the control of the sympathetic nervous system. Connective tissue around the artery is stained blue. Cardiac muscle tissue surrounds it.