Extracellular matrix that is a thin, sheet-like membrane comprised of endothelial and epithelial cells is called the...

• A. Hyaluronic acid
• B. Interstitium
• C. Basement membrane
• D. Collagen

Answer: (C)

A basement membrane is a thin, sheet-like extracellular matrix that sits between epithelial or endothelial cells and the underlying connective tissue. It’s produced by the nearby cells and consists mainly of type IV collagen and laminin, along with other components like nidogen and proteoglycans. This specialized layer provides structural support, helps cells attach and polarize, and acts as a selective barrier in filtration processes (think the kidney and lungs). Hyaluronic acid is a soluble component of the ECM, not a distinct sheet; the interstitium is the connective tissue space beneath the basement membrane; collagen is a major structural protein but typically forms fibers rather than the thin sheet separating layers.