DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Scanning electron micrograph (SEM) of a blood clot (menstrual). Human red blood cells are trapped in fibrin. Platelets are cell fragments in the blood that play an essential role in blood clotting and wound repair. Platelets in the blood are small oval disks and are termed non-activated platelets or thrombocytes. They serve as the body's first line of defence to prevent excessive blood loss. When an injury such as a cut is sustained, platelets change their shape (now known as activated platelets), become sticky and build up on a vessel wall to form a plug. They are also involved in the secretion of a chemical platelet factor which helps produce threads of fibrin. Bloods cells collect in the entangled fibrin and platelet mass forming a blood clot at the site. Magnification: x10,000 when shortest axis printed at 25 millimetres.
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