What is the purpose of the basement membrane?

• A. It forms the apical surface.
• B. It separates underlying connective tissue from the epithelium.
• C. It provides nutrition to epithelial cells.
• D. It binds epithelial cells together.

Answer: (B)

Basement membranes are thin extracellular matrices that sit between the epithelium and the underlying connective tissue. Their primary role is to separate these two tissue layers while providing a stable anchor for epithelial cells through attachments like hemidesmosomes to the membrane. They also act as a selective barrier and influence how epithelial cells grow and differentiate, guiding tissue organization and repair. Nutrients to epithelial cells come from the blood vessels in the connective tissue and reach the epithelium by diffusion across this barrier—not by the basement membrane supplying nutrients directly. The apical surface is formed by the epithelial cells facing the lumen, not by the basement membrane. Binding of epithelial cells to each other is accomplished by cell junctions between the cells, not by the basement membrane.