So this is known as the extracellular matrix, and there are three major constituents of the extracellular matrix. So we have structural proteins, Adhesive proteins and proteoglycan. So once again, groups of cells that carry out a similar function are called tissues. And different tissues have different composition of their extracellular matrix. So the extracellular matrix or ECM, is a collection of all the molecules and fibers that are found outside the cells, that hold the individual cells together to form our tissues. And there are three major molecules that constitute our ECM or extracellular matrix.