STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Human blood cells, Scanning electron micrograph (SEM) of a variety of blood cells from the site of an early skin wound. Red and white blood cells (two cells top center) as well as activated platelets (bottom left) are present. Platelets are tiny blood cells that help the body form clots to stop bleeding. If a blood vessels gets damaged, it sends out signals that are picked up by platelets. The platelets then rush to the site of damage and form a plug, or clot, to repair the damage. The process of spreading across the surface of a damaged blood vessel to stop bleeding is called adhesion. This is because when platelets get to the site of the injury, they grow sticky tentacles that help them adhere. They also send out chemical signals to attract more platelets to pile onto the clot in a process called aggregation. Magnification: x5000 when printed 10cm wide.
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