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Composition
The basement membrane is the fusion of two basal laminae. It consists of an electron-dense membrane called the lamina densa, about 30–70 nanometers in thickness, and an underlying network of reticular collagen (type III) fibrils (its precursor is fibroblasts) which average 30 nanometers in diameter and 0.1–2 micrometers in thickness. This type III collagen is of the reticular type, in contrast to the fibrillar collagen found in the interstitial matrix.12 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)3 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.4
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.5 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.6
The most notable examples of basement membranes is in the glomerular filtration of the kidney, by the fusion of the basal lamina from the endothelium of glomerular capillaries and the basal lamina of the epithelium of the Bowman's capsule, and between lung alveoli and pulmonary capillaries, by the fusion of the basal lamina of the lung alveoli and of the basal lamina of the lung capillaries, which is where oxygen and CO2 diffusion happens. Basement membrane is non cellular.
Noncollagenous domain basement membrane collagen type IV is autoantigen (target antigen) of autoantibodies in the autoimmune disease Goodpasture's syndrome.7
See also
References
- ^ Kumar, Abbas, Fausto; Robbins and Cotran: Pathologic Basis of Disease; Elsevier, 7th ed.
- ^ Stanley JR, Woodley DT, Katz SI, Martin GR; Structure and function of basement membrane.; J Invest Dermatol. 1982 Jul;79 Suppl 1:69s-72s.
- ^ DM Noonan, A Fulle, P Valente, S Cai, E Horigan, M Sasaki, Y Yamada and JR Hassell; The complete sequence of perlecan, a basement membrane heparan sulfate proteoglycan, reveals extensive similarity with laminin A chain, low density lipoprotein-receptor, and the neural cell adhesion molecule; J. Biol. Chem., Vol. 266, Issue 34, 22939-22947, 12, 1991
- ^ M Paulsson; Basement membrane proteins: structure, assembly, and cellular interactions; Critical Reviews in Biochemistry and Molecular Biology, Vol 27, Issue 1, 93-127, 1992
- ^ L. A. Liotta, K. Tryggvason, S. Garbisa, Ian Hart, C. M. Foltz & S. Shafie; Metastatic potential correlates with enzymatic degradation of basement membrane collagen; Nature 284, 67 - 68 (6 March 1980).
- ^ Y Kubota, HK Kleinman, GR Martin and TJ Lawley; Role of laminin and basement membrane in the morphological differentiation of human endothelial cells into capillary-like structures; The Journal of Cell Biology, Vol 107, 1589-1598.
- ^ Janeway,Travers, Walport, Shlomchik; Immunobiology 5th ed.
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