出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/04/03 12:41:50」(JST)
| Basal lamina | |
|---|---|
| Basal lamina lining outer surface of cell membrane | |
| Latin | lamina basalis |
| Code | TH H2.00.00.0.00006 |
The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often confused with the basement membrane, and sometimes used inconsistently in the literature, see below.
This structure is visible only with the electron microscope, where it appears as an electron-dense layer, 20-100 nm thick(with exceptions such as the basal laminae that compose the 100-200 nanometre thick glomerular basement membrane).
The best known macromolecular components of basal laminae are laminin, type IV collagen, entanctin and perlecan. All these components are secreted at the basal poles of the epithelial cells. Their precise porportions in basal laminae vary between and within tissues. Basal laminae are attached to reticular fibers made of type III collagen in the underlying connective tissues by anchoring fibrils of type VII collagen. These proteins, that are produced by cells of the connective tissue, form a layer below the basal lamina called the reticular lamina.
Basal laminae have many functions. In addition to simple structural and filtering functions, they are also able to influence cell polarity; regulate cell proliferation and differenciation by binding and concentrating growth factors, influence cell metabolism and survival; organize proteins in the adjacent plasma membrane; and serve as pathways for cell migration. [1]
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The layers of the basal lamina ("BL") and those of the basement membrane ("BM") are described below:
| Name | Part of BL? | Part of BM? | Notes |
| lamina lucida / lamina rara interna[2] | yes | yes | electron-lucid layer[3] containing the glycoprotein laminin |
| lamina densa | yes | yes | electron-dense layer[4] composed of type IV collagen |
| lamina lucida / lamina rara externa | yes | yes | Similar composition to lamina rara interna. Some sources do not consider this a distinct layer. |
| lamina reticularis[5] | no | yes | The three above layers of the basal lamina typically sit on top of the reticular lamina, which is synthesized by cells from the underlying connective tissue and contains fibronectin. The exception is when two epithelial layers abut one another as in the alveoli of the lungs and glomeruli of the kidneys, in which the basal lamina of one epithelial layer fuses with that of the other. |
Anchoring fibrils composed of type VII collagen extend from the basal lamina into the underlying reticular lamina and loop around collagen bundles. Although found beneath all basal laminae, they are especially numerous in stratified squamous cells of the skin.
These layers should not be confused with the lamina propria, which is found outside the basal lamina.[6]
The term "basal lamina" is usually used with electron microscopy, while the term "basement membrane" is usually used with light microscopy. Basement membrane is used to specify a periodic acid-Schidd (PAS)-positive layer, visible with the light microscope beneath epithelia. The basement membrane is formed by the combination of a basal lamina and a reticular lamina and is therefore thicker.
The basal lamina cannot be distinguished under the light microscope, but under the higher magnification of an electron microscope, the basal lamina and lamina reticularis are visibly distinct structures.
Some theorize that the lamina lucida is an artifact created when preparing the tissue, and that the basement membrane is therefore equal to the lamina densa in vivo.[7]
Examples of basement membranes include:
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| リンク元 | 「基底膜」「精細管」「基底板」「BM」「basement lamina」 |
| 拡張検索 | 「basal laminae」 |
| 関連記事 | 「basal」 |