There is still lack of agreement about the extent to which the basal lamina seen with the EM corresponds to the structure described as the basement membrane in the light microscope. Some investigators contend that the basement membrane includes not only the basal lamina but also a secondary layer of small-unit fibrils of type III collagen (reticular fbers) that forms the reticular lamina. The reticular lamina, as such, belongs to the connective tissue and is not a product of the epithelium. The reticular lamina was once regarded as the component that reacted with silver, whereas the polysaccharides of the basal lamina and the ground substance associated with the reticular fibers were thought to be the components stained with the PAS reaction. However, convincing arguments can be made for the basal lamina reacting with both PAS and silver in several sites. In normal kidney glomeruli, for example, no collagen (reticular) fibers are associated with the basal lamina of the epithelial cells (Fig. 5.32), although a positive reaction occurs with both PAS staining and silver impregnation. Also, in the spleen, where the basal lamina of the venous sinuses forms a unique pattern of ringlike bands rather than a thin, sheathlike layer around the vessel, exactly corresponding images are seen with the PAS and silver techniques as well as with the EM (Fig. 5.33).
Several structures are responsible for attachment of the basal lamina to the underlying connective tissue.
On the opposite side of the basal lamina, the connective tissue side, several mechanisms provide attachment of the basal lamina to the underlying connective tissue:  Anchoring fbrils (type VII collagen) are usually found in close association with hemidesmosomes. They extend from the basal lamina either to the structures called anchoring plaques in the connective tissue matrix or loop back to the basal lamina (Fig. 5.34). The anchoring fibrils entrap type III collagen (reticular) fibers in the underlying connective tissue, which ensures sound epithelial anchorage. Anchoring fibrils are critical to the function of the anchoring junctions; mutations in the collagen VII gene result in dystrophic epidermolysis bullosa, an inherited blistering skin disease in which the epithelium is detached below the basement membrane.
 Fibrillin microfbrils are 10 to 12 nm in diameter and attach the lamina densa to elastic fibers. Fibrillin microfibrils are known to have elastic properties. A mutation in the fibrillin gene (FBN1) causes Marfan’s syndrome and other related connective tissue disorders.
 Discrete projections of the lamina densa on its connective tissue side interact directly with the reticular lamina to form an additional binding site with type III collagen.
An interwoven network of proteins provides the bases for a variety of basal lamina functions.
In recent years, the basal lamina has been recognized as an important regulator of cell behavior rather than just a structural feature of the epithelial tissue. Organ-specific molecules have been identified in the basal lamina. Although morphologically single molecule of laminin integrin receptors