2. Matrix Chemistry
The most typical form of ECM is that found in connective tissue, which is the mixture of cells and ECM found in much of the body. The connective tissue is surrounded by specialised ECM called the basal lamina, which underlies epithelial cells. Immune cells are often present too, but these are for defense, not for generation of ECM: connective tissue is primarily generated by fibroblasts. Specialised fibroblasts include chondroblasts (which secrete cartilage) and osteoblasts (which secrete bone).
The ECM is composed of a mixture or water, proteins and carbohydrates. The main macromolecular components of the ECM are glycosaminoglycans (GAGs, acidic polysaccharide derivatives); proteins such as collagen, elastin, fibronectin and laminin; and proteoglycans, which are proteins with GAGs attached to them covalently.
Molecular Components
Components of the ECM are produced intracellularly by resident cells, and secreted into the ECM via exocytosis. Once secreted they then aggregate with the existing matrix. The ECM is composed of an interlocking mesh of fibrous proteins and glycosaminoglycans (GAGs).