What type of collagen predominates in epithelial basement membranes and the glomerular basement membrane?

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

Answer: (D)

Basement membranes are built mainly from a network-forming type IV collagen, not the fibrillar collagens that form most connective tissue fibers. In epithelial basement membranes (the basal lamina) and in the glomerular basement membrane of the kidney, type IV collagen provides a sheet-like scaffold along with laminin, proteoglycans, and other components. The other collagens—type I in skin, bone, and tendon; type II in cartilage; type III in reticular fibers of soft tissues—form fibrils rather than the basement-membrane network. So the predominating collagen in these basement membranes is type IV, the network-forming variety.