Which collagen type predominates in the basal lamina of basement membranes?

• A. Type I
• B. Type II
• C. Type III
• D. Type IV

Answer: (D)

The basal lamina is a thin, sheet-like part of the basement membrane secreted by epithelial cells, and its collagen component is Type IV. Type IV collagen forms a two-dimensional, crosslinked network rather than thick fibrils, creating a supportive scaffold that works with laminin to anchor epithelial cells and provide filtration and selective barriers in tissues such as the kidney. In contrast, the fibrillar collagens (Types I, II, III) build strong, rope-like fibers in connective tissues, not the basal lamina. The reticular lamina beneath the basal lamina contains different collagens (notably Type III), and anchoring structures connect these layers, but the basal lamina itself is predominantly Type IV.