Basal lamina
| Basal lamina | |
|---|---|
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| Details | |
| Identifiers | |
| Latin | lamina basalis |
| Code | TH H2.00.00.0.00006 |
| TA |
A15.2.03.007 A15.2.03.019 |
| FMA | 62918 58438, 62918 |
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Anatomical terminology
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The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often incorrectly referred to as the basement membrane, though it does constitute a portion of the basement membrane. The basal lamina is visible only with the electron microscope, where it appears as an electron-dense layer that is 20-100 nm thick (with some exceptions that are thicker, such as basal lamina in lung alveoli and renal glomeruli).
The layers of the basal lamina ("BL") and those of the basement membrane ("BM") are described below:
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.
The basement membrane is visible under light microscopy. Electron microscopy shows that the basement membrane consists of three layers: the lamina lucida (electron-lucent), lamina densa (electron-dense), and lamina fibroreticularis (electron-lucent).
The lamina densa was formerly known as the basal lamina. The terms basal lamina and basement membrane were often used interchangeably, until it was realised that all three layers seen with the electron microscope represent the single layer seen with the light microscope. This has led to considerable terminological confusion and, if used, the term basal lamina should be confined to its meaning as lamina densa.
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.
The term "basal lamina" is usually used with electron microscopy, while the term "basement membrane" is usually used with light microscopy.
Examples of basement membranes include:
The basal lamina is made and maintained by the cells that sit on it. It acts as a point of attachment for cells. However, it can also have other function such as a permeability barrier in the glomerulus (urine production).
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