basement membrane (basal lamina) A thin sheet of fibrous proteins that underlies and supports the cells of an epithelium, separating this from underlying tissue. Such membranes also surround muscle cells, Schwann cells, and fat cells, and a thick basement membrane is found in the kidney glomerulus, where it acts as a filter (see ultrafiltration). Basement membranes are components of the extracellular matrix and help to regulate passage of materials between epithelial cells and adjacent blood vessels. Each consists of a framework of collagen fibrils, within which are glycosaminoglycans (mucopolysaccharides) and laminins, which are proteins that bind the basement membrane to neighbouring cells via cell adhesion molecules.

basement membrane See BASAL LAMINA.

basement membrane (bayss-mĕnt) n. the thin delicate membrane that lies at the base of an epithelium.