Composition
The basement membrane is the fusion of two lamina, the basal lamina and the reticular lamina (or lamina reticularis). The lamina reticularis is attached to the basal lamina with anchoring fibrils (type VII collagen fibers) and microfibrils (fibrillin). The two layers are collectively known as the basement membrane.
The basal lamina layer can further be divided into two layers. The clear layer closer to the epithelium is called the lamina lucida, while the dense layer closer to the connective tissue is called the lamina densa. The electron-dense lamina densa membrane is about 30–70 nanometers in thickness, and consists of an underlying network of reticular collagen (type IV) fibrils (fibroblast precursors) which average 30 nanometers in diameter and 0.1–2 micrometers in thickness. In addition to collagen, this supportive matrix contains intrinsic macromolecular components.
The Lamina Densa (which is made up of type IV collagen fibers; perlecan (a heparan sulfate proteoglycan) coats these fibers and they are high in heparan sulfate) and the Lamina Lucida (made up of laminin, integrins, entactins, and dystroglycans) together make up the basal lamina.
Integrins are not part of the basement lamina, they are part of desmisomes which are in the basement membrane but not the basement lamina. To represent the above in a visually organised manner, the basement membrane is organized as follows:
- Epithelial Tissue (outer)
Read more about this topic: Basement Membrane
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