Artery. Light micrograph of a cross-section through a healthy human artery. At top is the lumen (inner cavity) of the artery through which blood flows. The inner endothelial wall (pink) appears folded, consisting of a layer of flattened epithelial cells and elastic connective tissue. Beneath it is a thick tunica media layer (grey) containing elastic fibres and smooth muscle which enables the artery to expand and recoil with the blood flow. The tunica adventitia (at lower frame) contains loosely arranged collagenous fibres as the outer layer of the artery. Arteries transport oxygenated blood from the heart around the body. Magnification: x25 at 35mm size.