Connective tissue ground substance

Ground substance

The ground substance is an amorphous gel-like material composed of polysaccharide chains (glycosaminoglycans) bound to protein.

With LM, in H & E sections, they are not visible when present in low concentration. However, at higher concentration (as in hyaline cartilage), they stain basophilic. When stained with toluidine blue or crystal violet, they are metachromatic (take a different color than the color of the dye used). The ground substance includes two major groups:

1. Non-sulfated glycosaminoglycans (hyaluronic acid)

The hyaluronic acid consists of long molecule that form a network whose spaces are filled with tissue fluid forming gel-like material. The hyaluronic acid predominate in loose connective tissue, vitreous humor, synovial fluid and umbilical cords.

2. Sulfated glycosaminoglycans

Chondroitin-4-sulfate and chondroitin-6-sulfate are abundant in cartilage, bone, skin, and cornea.

Dermatan sulfate is found in skin, tendon, ligamentum nuchae, sclera and lung.

Keratan sulfate is present in cartilage, bone and cornea.

Heparan sulfate in arteries and lung.

Heparin in mast cells, in lung, liver and skin.

Functions of the ground substance

The glycosaminoglycans and proteoglycans are highly hydrophilic. The tissue fluid within the meshes permits the diffusion of nutrients and metabolites between the connective tissue cells and circulatory system.

The gel-like nature of the hyaluronic acid is thought to act as a barrier against the spread of bacteria that may enter the tissues. Invasive bacteria produce the enzyme hyaluronidase that facilitates their spread.