(Science: protein) glycoprotein of high molecular weight (2 chains each of 250 kd linked by disulphide bonds) that occurs in insoluble fibrillar form in extracellular matrix of animal tissues and soluble in plasma, the latter previously known as cold insoluble globulin. The various slightly different forms of fibronectin appear to be generated by tissue specific differential splicing of fibronectin mrna, transcribed from a single gene. Fibronectins have multiple domains that confer the ability to interact with many extracellular substances such as collagen, fibrin and heparin and also with specific membrane receptors on responsive cells. Notable is the RGD domain recognised by integrins and two repeats of the egf like domain. Interaction of a cells fibronectin receptors (members of the integrin family) with fibronectin adsorbed to a surface results in adhesion and spreading of the cell.