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Activated platelets. When they encounter a damaged blood vessel they become activated and secrete chemical mediators, including serotonin, which cause the blood to clot. The mediators convert soluble fibrinogen to the insoluble protein fibrin. The resulting fibrin mesh traps platelets and red and white blood cells, forming a plug that seals the damaged vessel.
The Cell (January 2011) How can cells grow and develop to form complex creatures? In this issue we explore the secrets of the cell. Our free poster shows a typical animal cell and reveals some surprising statistics. Order a copy or download [PDF].