Basalmembranet

Basalmembranet, or basement membrane, is a thin, specialized extracellular matrix that underlies epithelial and endothelial cell layers and surrounds certain non-epithelial structures such as muscle fibers, adipocytes, and Schwann cells. It forms a dense, continuous sheet that separates the epithelium or endothelium from the underlying connective tissue and provides structural support.

Its organization includes two principal components: the basal lamina (basal lamina) and the reticular lamina. The basal lamina is produced by the overlying cells and is rich in laminins, type IV collagen, nidogens (entactin), and heparan sulfate proteoglycans such as perlecan. The reticular lamina is produced by surrounding connective tissue and contains type III collagen and other extracellular matrix proteins; anchoring fibrils of type VII collagen help attach the basal lamina to the reticular lamina. Cell adhesion receptors, including integrins and dystroglycan, mediate attachment to the basal lamina and influence cell behavior.

Functions include providing mechanical support, regulating filtration and molecule passage (notably in the kidney), guiding cell adhesion, polarity, migration, and differentiation, and forming a template for tissue development and repair. Remodeling of the basement membrane is common in development, wound healing, inflammation, and cancer, and abnormal basement membrane composition is linked to diseases such as inherited nephropathies caused by COL4A5 mutations or LAMB2 defects, and autoimmune diseases targeting basement membrane components.