The matrix is composed of a variety of polysaccharides and proteins. ECM is present to some degree in all tissues, even blood where the plasma might be considered the matrix, but is a functional determinant in connective tissues. The proteoglycans retain water and form a sort of gel substance through which ions, hormones and nutrients can freely move. Indeed the ground substance can act as a molecular sieve to regulate the traffic of molecules and cells according to charge or size. A chief component of ground substance is hyaluronic acid which is a large polysaccharide made of glucuronic acid and glucosamine that attracts water and is increased in tissues under repair or growth.
Cells can easily migrate through swelled hyaluronic acid ground substance.
It also serves as a lubricant in joint fluid.