BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Platelets. Coloured Scanning Electron Micrograph (SEM) of activated blood platelets. Platelets (thrombocytes) are the smallest blood cells. Unactivated platelets are oval shaped, while activated platelets (as seen here) have dendritic processes or pseudopodia. They are non-nucleated cells formed in the bone marrow. Platelets survive for about 9 days. They function in two ways. First, they help plug defects in the walls of damaged blood vessels. Secondly, they are involved in clotting and the release of serotonin, a compound which reduces blood flow by constricting the damaged vessels. Magnification: unknown.
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