Platelets don’t reproduce. The average lifespan of a platelet is 8-9 days. All of our blood cells are made in our bone marrow from stem cells that differentiate into all of the different types of blood cells we have. Your marrow is constantly making new platelets (and other blood cells) to replace ones that have worn out. Platelets, like all blood cells, circulate freely in your blood. When a blood vessel is damaged and blood leaks out, there will be platelets already there. They stick to the edges of the wound and release chemicals that attract more platelets to plug the wound. Other chemicals in your blood called clotting factors cause strands of a protein called fibrin to stick together and seal the inside of the wound
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