Caption: Activated (yellow, filopodial extensions) and nonactivated (brown, smooth, discoid) platelets around a red blood cell. Channels of the open canalicular system (OCS) are still present. Platelets are cell fragments in the blood that play an essential role in blood clotting and wound repair. Platelets can also activate certain immune responses. Platelets are formed in the red bone marrow, lungs, and spleen by fragmentation of very large cells known as megakaryocytes. Platelets in the blood are small oval disks and are termed nonactivated platelets or thrombocytes. Platelets serve as the body's first line of defense to prevent excessive blood loss. When an injury such as a cut is sustained, platelets (now known as activated platelets) change their shape, become sticky and build up on a vessel wall to form a plug. They are also involved in the secretion of a chemical platelet factors which helps produce threads of fibrin. Blood cells collect in the entangled fibrin and platelet mass forming a blood clot at the site.
Magnification*: x1, 600
Type: SEM
Copyright 2000 Dennis Kunkel Microscopy, Inc.
Keywords: human body,blood,human,platelet,activated platelet,open canalicular system,OCS,thrombocyte,thrombocytes,clot,red blood cell,SEM,03.01.09,20350A