Which molecule is a viscous mucopolysaccharide found in the vitreous humor, the umbilical cord, and synovial fluid, and acts as a cementing substance?

• A. Chondroitin sulfate
• B. Keratan sulfate
• C. Dermatan sulfate
• D. Hyaluronic acid

Answer: (D)

Hyaluronic acid carries the essential trait of forming a very large, hydrated gel that gives viscosity and lubrication in several body fluids. This non-sulfated glycosaminoglycan is abundant in the vitreous humor, where its high-water–binding capacity maintains the gel-like structure; in synovial fluid it provides the slippery, viscoelastic property necessary for smooth joint movement; and in the umbilical cord (Wharton’s jelly) it creates a soft, cushiony matrix. Its role as a cementing substance arises from its ability to bind water and interact with other ECM components to create a hydrated, space-filling network that stabilizes tissues and facilitates smooth movement. The other glycosaminoglycans listed are sulfated and typically exist as parts of proteoglycans in cartilage and connective tissues, contributing to structure but not delivering the same viscous, gel-like properties in these fluids as hyaluronic acid.