DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Human bone marrow megakaryocyte and platelet formation, scanning electron micrograph (SEM). A large megakaryocyte in the process of forming 2 small platelets via proplatelet extensions. During megakaryocyte maturation the cell grows in size and replicates its DNA (deoxyribonucleic acid) 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. Megakaryocytes are responsible for the production of platelets, which are necessary for normal blood clotting. 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. Magnification: x1,600 when shortest axis printed at 25 millimetres.
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