the disk in the fundus of the eye marking the point at which the optic nerve enters; it is accompanied by blood vessels, is oval, light in color and the blind spot of the retina.
ARTERIOLES. In arterioles, the tunica intima consists of a continuous endothelium and a very thin subendothelial layer. In addition, a thin, fenestrated internal elastic lamina is present in larger arterioles but absent in terminal arterioles. Generally, the tunica media consists of 2 layers of smooth muscle cells.
Extensible elastic fibres (containing the protein elastin) form networks, e.g. in the walls of arteries and in the lungs, and are a component of flexible cartilage (such as in the nose and ears); reticular fibres form delicate networks, e.g. in the skin deep to the epidermis, and in the walls of small blood vessels.