The Basement membrane is an extracellular structure which separates the Epidermis from the Dermis; it allows both structures to “stick” to each other.
It is composed of the fusion of two layers, the basal lamina (of epidermal origin) and the underlying layer of reticular connective tissue (dermal origin).
Under the electron microscope, two parts can be distinguished, a dense lamina densa which consists mainly of collagen IV and a light lamina lucida
In terms of molecular structure the lamina densa includes collagen (type III, IV and VII) and the lamina lucida: laminin, hemidesmosomes. The latter are attached to the basal keratinocytes and the epidermal stem cells.
It is essential for for the epidermal structure to stick tightly to the rest of the skin. It is itself firmly in contact to the dermis with anchoring fibrils (collagen 7) and Surface adhesion molecules (SAM).
The basement membrane is not normally visible under optical microscopy except in pathological states (such as systemic lupus erythematosus). It is always visible under electron microscopy.
It is difficult to image its plane structure (like a piece of paper) when seen in conventional sections perpendicular to the skin.
However it is a plane and separates the epidermis from the dermis.
It is permeable and can therefore act as a barrier and filter passage of nutrients, inflammatory signals…between the two components of the skin.
It prevents malignant cells from entering the dermis (In Situ vs invasive cancers)
It is also essential for angiogenesis (development of new blood vessels). Basement membrane proteins have been found to accelerate differentiation of endothelial cells.
As you know, the epidermis is NOT vascularized which means that inflammatory cells such as lymphocytes and histiocytes need to leave the blood stream to reach the dermis (margination, rolling, diapedesis). Only then do they release cytokines (These cytokines then migrate to the epidermis which lead to reduced keratinocyte differentiation and increased turnover.
It is thickened in lupus erythematosus. It might play a role in Psoriasis (click HERE to read more). Many proteins are absent or mutated in a group of blistering diseases called Epidermolysis Bullosa
+41 22 738 18 48