Basement membrane



The basement membrane is a structure that supports overlying epithelial or endothelial cells.

Composition
The basement membrane consists of an electron-dense membrane called the lamina densa, about 30–70 nanometers in thickness, and an underlying network of reticular collagen (type IV) fibrils (its precursor is fibroblasts) which average 30 nanometers in diameter and 0.1–2 micrometers in thickness. This type IV collagen is of the reticular type, in contrast to the fibrillar collagen found in the interstitial matrix. In addition to collagen, this supportive matrix contains intrinsic macromolecular components.

The Lamina Densa (which is made up of type IV collagen fibers; perlecan (a heparan sulfate proteoglycan) coats these fibers and they are high in heparan sulfate) and the Lamina Lucida (made up of laminin, integrins, entactins, and dystroglycans) together make up the basal lamina. Lamina Reticularis attached to basal lamina with anchoring fibrils (type VII collagen fibers) and microfibrils (fibrilin) is collectively known as the basement membrane.

Function and importance
The primary function of the basement membrane is to anchor down the epithelium to its loose connective tissue underneath. This is achieved by cell-matrix adhesions through cell adhesion molecules (CAMs).

The basement membrane acts as a mechanical barrier, preventing malignant cells from invading the deeper tissues. Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are called carcinoma in situ.

The basement membrane is also essential for angiogenesis (development of new blood vessels). Basement membrane proteins have been found to accelerate differentiation of endothelial cells.

It also plays an important role in glomerular filtration in the kidney.

Noncollagenous domain basement membrane collagen type IV is autoantigen (target antigen) of autoantibodies in the autoimmune disease Goodpasture's syndrome.