Description: Human bone marrow megakaryocyte and proplatelet / platelet formation. Shown in this image is a large megakaryocyte in the process of forming 2 small platelets via proplatelet extensions. Megakaryocytes are derived from hematopoietic stem cell precursor cells in the bone marrow. During megakaryocyte maturation the cell grows in size and replicates its DNA without cytokinesis (a process called endomitosis). As a result, the nucleus of the megakaryocyte is polyploid and may contain up to 32 copies of the normal complement of DNA in a human cell. Megakaryocytes are responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting. 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 can be seen forming along the proplatelet processes. 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. Thrombopoietin plays a role in inducing the megakaryocyte to form small proplatelet processes that then form immature platelets and eventually mature blood platelets.
Type: SEM
Magnification:* x1,600
Copyright 2011 Dennis Kunkel Microscopy, Inc.
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