Basement membranes are a specialized form of connective tissue. They form extracellular matrices and are distributed in almost all organs of the body. The nature of basement membranes has been the subject of several investigations, which include studies dealing with the morphology, chemistry, immunology, biosynthesis, and function of these substances. Basement membranes are found adjacent to the endothelial cell layer of blood vessels and capillaries, the epithelial layers of skin, viscera and glands, the specialized tissues of the eye, that is, the lens capsule epithelium, Bowman's epithelium of the cornea, the endothelium of Descemet's membrane, and the embryonic layers of the parietal and visceral yolk sac. The functions of basement membranes are: support and selective filtration. Basement membranes are not related structurally, chemically, or immunologically to the limiting plasma membranes of cells or to the membranes of intracellular organelles.
