basementmembrane

The basement membrane is a specialized, sheet‑like extracellular matrix that separates the epithelium or endothelium from the underlying connective tissue. It is found at all epithelial sites, including the skin, kidney, lung, and reproductive tract, as well as at the interface between the gut epithelium and its mesenchyme. The basement membrane provides structural support, acts as a selective filter for solutes and cells, and plays critical roles in cell signaling, migration, and differentiation.

Anatomically, the basement membrane is composed of a basal lamina and an interstitial layer. The basal lamina is thinned and contains laminin, type IV collagen, nidogen, and heparan sulfate proteoglycans. The interstitial component, often called the lamina densa or lamina reticularis, contains type IV collagen, entactin, and other matrix proteins. The arrangement of these components creates a lattice-like mesh that is highly organized, yet permeable to nutrients, gases and small proteins such as albumin while restricting the passage of larger molecules.

The basement membrane influences many cellular processes. It mediates attachment of cells through integrin receptors, regulates cell polarity, and modulates growth factor availability. It also aids in wound healing by guiding keratinocyte and endothelial cell migration. In diseases, disruption or aberrant remodeling of basement membranes is implicated in conditions such as Alport syndrome, nephrotic syndrome, diabetic nephropathy, and certain cancers. In cancer, basement membrane degradation allows tumor cells to invade underlying stroma and metastasize. Moreover, age‑related changes in basement membranes can affect tissue elasticity and repair capacity. Understanding the composition and function of basement membranes remains essential for elucidating normal physiology and pathogenesis across a broad spectrum of organ systems.