Fig. 3. Contractile non-muscle cells. (A) The arrangement of myofibroblasts in the body of a wound. Actin stress fibres (red) align along the long axis, and the cells exert contractile forces on the extracellular matrix, via integrins spanning the plasma membrane. Epithelial cells at the edge of the wound assemble actomyosin bundles that couple through adherens junctions to form a contractile `purse-string' structure that helps to close the wound. (B) Myoepithelial cells (blue) cover the external face of mammary ducts and contract in response to oxytocin to aid expulsion of milk. (C) Pericytes (blue) similarly cover endothelial cells in mature capillaries and provide contractile force to maintain tone and the passage of fluid.