Ground substance extracellular

I 38. Which of the substances below is primarily found in ground substance (extracellular matrix) ... 

Hyaluronic acid is a component of the extracellular ground substance which surrounds the collagen and elastin fibres and cells of connective tissue [64], It is a member of the group of polysaccharides isolated from vertebrate connective tissues which were formerly called mucopolysaccharides and are now more commonly referred to as glycosaminoglycans [65,66], Glycosaminoglycans commonly occur in vivo as proteoglycans. 

A. Proteoglycans are found in the extracellular matrix or ground substance of connective tissue, synovial fluid of joints, vitreous humor of the eye, secretions of mucus-producing cells, and in cartilage. 

The body s connective tissues can be classified as connective tissue proper (subdivided into loose and dense connective tissue proper), fluid connective tissues (subdivided into blood and lymph) and supporting connective tissues (subdivided into the cartilage and the bone). Fibroblasts are the most abundant permanent residents of the connective tissue proper and are the only cells always present in it. Fibroblasts secrete hyaluronans (a polysaccharide derivative) and proteins, both of which interact in the extracellular fluid to form proteoglycans that make ground substances viscous. They also secrete protein subunits that interact to form large extracellular fibres that could create loose/open framework or densely packed framework. 

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