- Epithelial cells rest on a thin basement membrane.

- In multi-layered epithelia, the deepest cells lie on this membrane.

- A distinct basement membrane cannot be seen in haematoxylin and eosin (H & E) preparations, but can be well demonstrated using the periodic acid Schiff (PAS) method. The latter stains the glycoproteins present in the membrane.

- Under the EM a basement membrane is seen to have a basal lamina (nearest the epithelial cells) and a reticular lamina or fibroreticular lamina (consisting of reticular tissue and merging into surrounding connective tissue). The basal lamina is divisible into the lamina densa containing fibrils; and the lamina lucida which appears to be transparent. The lamina lucida lies against the cell membranes of epithelial cells.

Functions of Basement membrane

- It provides adhesion on one side to epithelial cells (or parenchyma); and on the other side to connective tissue (mainly collagen fibres).

- It acts as a barrier to the diffusion of molecules. The barrier function varies with location (because of variations in pore size). Large proteins are prevented from passing out of blood vessels, but (in the lung) diffusion of gases is allowed.

- Recent work suggests that basement membranes may play a role in cell organisation, as molecules within the membrane interact with receptors on cell surfaces. Substances present in the membrane may influence morphogenesis of cells to which they are attached.

- The membranes may influence the regeneration of peripheral nerves after injury, and may play a role in re-establishment of neuromuscular junctions.