Which type of collagen would you expect to be in basement membranes?

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

Answer: (B)

Basement membranes are thin, sheet-like extracellular matrices that anchor epithelial and endothelial layers to the underlying connective tissue. The defining component is network-forming type IV collagen, which assembles into a two-dimensional mesh together with laminin, nidogen, and proteoglycans to create the supportive basement-laminar scaffold. This non-fibrillar collagen provides a flexible, continuous foundation that supports cells and regulates filtration and signaling.

In contrast, the other collagens are mainly fibrillar and form long fibers in different tissues: type I supports skin, bone, and tendon; type II is the main cartilage collagen; type III forms reticular fibers in loose connective tissue. Thus, the basement membrane’s characteristic collagen is type IV.