The Role of Platelets for Sealing of the Contracted DA. The scheme delineates the proposed sequence of events contributing to postnatal DA occlusion, which ultimately leads to permanent DA closure. As a result, the luminal aspect of the DA wall adopts a prothrombotic phenotype with endothelial activation, deposition of vWF and fibrin(ogen), and eventually endothelial cell detachment from the internal elastic lamina, leading to the collagen exposure. Together, this triggers the accumulation of platelets circulating in the residual DA lumen. The platelet plug that forms seals the residual lumen of the contracted DA and, together with other mechanisms, facilitates subsequent luminal remodeling.