Conceptual model of roles of FXIII-A in the formation of extracellular matrices. FXIII-A is best known as being activated by thrombin and covalently cross-linking and stabilizing the emergency matrix of fibrin formed when the blood coagulation cascade is activated. Cells undergoing growth and differentiation or responding to injury assemble fibronectin into fibrils that constitute a temporary working matrix and are used for multiple purposes depending on the cell type. Assembly is catalyzed by surface receptors that stretch fibronectin. In preadipocytes, assembly is enhanced by the FXIII-A. Finally, differentiated cells have a unique definitive matrix suited to their function. Each of the matrices has the potential to be adorned with other proteins. Cross-linking catalyzed by FXIII-A may contribute to some of the adornments. Professional illustration by Patrick Lane, ScEYEnce Studios.