DEE BREGER / SCIENCE PHOTO LIBRARY DEE BREGER / SCIENCE PHOTO LIBRARY
Blood clot. Coloured Scanning Electron Micrograph (SEM) of a blood clot. This is also known as a thrombus when it forms inside an intact blood vessel. Red blood cells (erythrocytes) are seen trapped in a web of fibrin threads. The fibrin is an insoluble protein and these threads are an essential mechanism for the arrest of bleeding. As the blood cells become trapped they lose their normal rounded shape (as seen at lower left). Blood clots form to repair blood vessels damaged by injury or disease. Abnormal clotting in blood vessels, as occurs in a thrombus, is the principal cause of heart attack and stroke. Sample of dog tissue.
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