Blood clot. Coloured scanning electron micrograph (SEM) of a blood clot from the inner wall of the left ventricle of a human heart. Red blood cells (erythrocytes) are trapped within a fibrin protein mesh (cream). The fibrin mesh is formed in response to chemicals secreted by platelets (pink), fragments of white blood cells. Clots are formed in response to cardiovascular disease or injuries to blood vessels. Connective tissue (orange) is also seen.
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Colored SEM of red and white blood cells inside a small blood vessel. The sample was prepared by freeze fracturing: rapidly freezing the sample with liquid nitrogen so that tissues are instantly preserved. When the sample is broken (fractured), the inner structures are revealed. In this frame, a tiny vein, or venule, has been opened to show the blood cells inside