Basal lamina

As a basement membrane is called a light- microscopically detectable reticular layer Argyrophilic fibrils and fibers under the epithelium, which is PAS positive due to their content of glycoproteins. According to an ancient mnemonic you find a basement membrane between different tissues, eg between epithelium and connective tissue.

The basal lamina

The only electron- microscopically detectable basal lamina, a protein appears to be homogeneous layer under the base of the epithelial cells is a component of basement membrane. It provides the link of the epithelial cells forth with the fibroretikulären, connective tissue basement membrane. It is a specialized extracellular matrix in which the dense network of reticular fibrils (lamina fibroretikularis ) is anchored to the basement membrane. It has an influence on cell metabolism, cell polarity and cell differentiation and is a guide rail for cell migrations. The basal lamina is composed of a light appearing lamina rara (also called lamina lucida ) and a darkly performing lamina densa. Of the basal lamina is followed by the reticular network of fibrils which forms the lamina fibroreticularis. In the light microscope, you can see the basement membrane, which is composed of the basal lamina and the lamina fibroreticularis. The lamina fibroreticularis but already part of the connective tissue.

The basal lamina is built up by the epithelial cells. Lamina rara and said underlying lamina densa together have a thickness of approximately 20 nm and consist mainly of the proteins collagen type IV and laminin, which is networked with the extracellular domains of integrins of the epithelial cell membranes, and entactin ( nidogen ) and proteoglycans such as perlecan. In addition, additional proteins may be associated with the targeted matrix components.

The basement membrane

When one speaks of the basement membrane, basal lamina comes to another layer: the lamina fibroreticularis, which consists of a network of reticular collagen fibrils. The entire layer of lamina rara and lamina densa lamina fibroreticularis has a thickness of about 1-2 microns.

In various tissues, there are structural differences in the composition of basement membranes, which are adapted to the respective requirements of the epithelium. Above all, can vary greatly here the composition of laminins.

Basal laminae also enclose muscle cells and nerve fibers. White ( univakuoläre, ie with a Fettvakuole ) adipocytes are also surrounded by a basal lamina -like layer.

Malignancy of many tumor diseases, inter alia, characterized in that the corresponding tumor cells are capable of, the basement membranes - especially by matrix metallo- proteinases ( MMPs) - decompose enzymatically. An invasion and metastasis of tumor cells into adjacent tissue is thus often possible.

• Cell Biology
• Epithelium