STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Blood clot. Coloured scanning electron micrograph (SEM) of a blood clot caused by an injury or disease. The clot consists of threads of fibrin (pink), an insoluble protein. These form a mesh which traps the disc-like red blood cells (erythrocytes) and seals the damaged blood vessel to prevent bleeding. Blood clots are triggered by chemicals released by platelet cells in the blood or by tissue cells at the injury site. These chemicals begin a complex series of reactions in the blood, resulting in fibrin formation. An abnormal clot, or thrombus, can occur in intact blood vessels, and is the main cause of heart attacks and strokes. Magnification unknown.
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