Passage: When tissue is first wounded, blood comes in contact with collagen, triggering blood platelets to begin secreting inflammatory factors.  Platelets also express sticky glycoproteins on their cell membranes that allow them to aggregate, forming a mass.Fibrin and fibronectin cross-link together and form a plug that traps proteins and particles and prevents further blood loss.  This fibrin-fibronectin plug is also the main structural support for the wound until collagen is deposited. Migratory cells use this plug as a matrix to crawl across, and platelets adhere to it and secrete factors. The clot is eventually lysed and replaced with granulation tissue and then later with collagen.

Question: What happens when blood contacts collagen?
triggering blood platelets to begin secreting inflammatory factors