| Basement membrane | |
|---|---|
 The epithelium and endobasement membrane in relation toepithelium andendothelium. Also seen are otherextracellular matrix components | |
 Image showing the basement membrane of thelining of the mouth, which separates the lining (epithelium) from a loose layer ofconnective tissue (thelamina propria) | |
| Details | |
| Identifiers | |
| Latin | membrana basalis |
| MeSH | D001485 |
| TH | H2.00.00.0.00005 |
| FMA | 63872 |
| Anatomical terms of microanatomy | |
Thebasement membrane, is a thin, pliable sheet-like type ofextracellular matrix that provides cell and tissue support, and acts as a platform for complexcell signaling.[1][2] The basement membrane sits betweenepithelial tissues includingmesothelium andendothelium, and the underlying connective tissue.[3][4]
As seen with theelectron microscope, the basement membrane is composed of two layers, thebasal lamina and thereticular lamina.[4] The underlying connective tissue attaches to the basal lamina withcollagen VIIanchoring fibrils andfibrillinmicrofibrils.[5]
The basal lamina layer can further be subdivided into two layers based on their visual appearance in electron microscopy. The lighter-colored layer closer to the epithelium is called thelamina lucida, while the denser-colored layer closer to the connective tissue is called thelamina densa. Theelectron-dense lamina densa layer is about 30–70nanometers thick and consists of an underlying network of reticularcollagen IV fibrils which average 30 nanometers in diameter and 0.1–2micrometers in thickness and are coated with the heparan sulfate-rich proteoglycanperlecan.[6] In addition to collagen, this supportive matrix contains intrinsic macromolecular components. The lamina lucida layer is made up oflaminin,integrins,entactins, anddystroglycans. Integrins are a key component ofhemidesmosomes which serve to anchor the epithelium to the underlying basement membrane.
To represent the above in a visually organised manner, the basement membrane is organized as follows:
The primary function of the basement membrane is to anchor down theepithelium to its looseconnective tissue (thedermis orlamina propria) underneath. This is achieved by cell-matrix adhesions throughsubstrate adhesion molecules (SAMs).
The basement membrane acts as a mechanical barrier, preventingmalignant cells from invading the deeper tissues.[7] Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are calledcarcinoma in situ.
The basement membrane is also essential forangiogenesis (development of new blood vessels). Basement membrane proteins have been found to acceleratedifferentiation ofendothelial cells.[8]
The most notable examples of basement membranes are theglomerular basement membrane of thekidney, by the fusion of thebasal lamina from theendothelium of glomerular capillaries and thepodocyte basal lamina,[9] and between thealveoli andcapillaries of thelung, 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 occurs (gas exchange).
As of 2017, other roles for basement membrane include blood filtration and muscle homeostasis.[1]Fractones may be a type of basement membrane, serving as aniche forstem cells.[10][11]
Some diseases result from a poorly functioning basement membrane. The cause can be genetic defects, injuries by the body's own immune system, or other mechanisms.[12] Diseases involving basement membranes at multiple locations include:
Inhistopathology, thickened basement membranes are found in several inflammatory diseases, such aslichen sclerosus,systemic lupus erythematosus ordermatomyositis in the skin, or collagenous colitis in the colon.[15]
These are only found withindiploblastic andhomoscleromorphic sponge animals. The homoscleromorph were found to be sister to diploblasts in some studies, making the membrane originate once in the history of life. But more recent studies have disregarded diploblast-homoscleromorph group, so other sponges may have lost it (most probable) or the origin in the two groups may be separate.
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