Description: Newly formed platelet (thrombocyte) after megakaryocyte differentiation. Platelets are formed in the red bone marrow, lungs, and spleen by fragmentation of very large cells known as megakaryocytes. Megakaryocytes release mature platelets in a complex process. Platelet production begins with the extension of large pseudopodia from the megakaryocyte cell surface that form thin tube-like cytoplasmic extensions (with bulbous thickenings) called proplatelets. As the proplatelet development continues small platelets are formed along the proplatelet processes. Thrombopoietin plays a role in inducing the megakaryocytes to form small proplatelet processes that then form immature platelets and eventually mature blood platelets. Shown in this image is a newly formed, mature, activated platelet after megakaryocyte differentiation. Mature activated platelets have numerous cytoplasmic extensions and channels of the open canalicular system (OCS) seen in this image. Each megakaryocyte produces and releases hundreds of platelets into the circulatory system. Nearly a trillion platelets circulate in an adult human and respond to blood vessel injury by changing shape, secreting granule contents, and aggregating. Platelets play an essential role in blood clotting and wound repair. They can also activate certain immune responses. Platelets in the blood are small oval disks and are termed nonactivated platelets (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 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.
Type: SEM
Magnification:* x5,335
Copyright 2011 Dennis Kunkel Microscopy, Inc.
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