Topic 37- Thrombocytopoesis – formation of thrombocytes (platelets)
Explains how platelets form in red bone marrow from megakaryocytes, starting from myeloid progenitors and passing through promegakaryocytes, then how megakaryocytes release proplatelets that break up into platelets. Covers regulation by thrombopoietin and its negative feedback, output figures per megakaryocyte and per day, platelet lifespan, removal by macrophages and splenic storage, and comparative size and nuclear features of megakaryoblasts and megakaryocytes.
Topic 37 of 59 in the MU Pleven syllabus for Cytology (Medicine, Year 1). The free AceMed note covers it in 2 sections, about 241 words (2 min of reading), with 13 flashcards.
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Topic 37- Thrombocytopoesis – formation of thrombocytes (platelets)
Thrombocytopoiesis – formation of thrombocytes (platelets)
Thrombocytopoiesis – formation of thrombocytes (platelets)
Platelets originate in the red bone marrow from megakaryocytes, which differentiate further from megakaryoblasts in a process driven by thrombopoietin
Thrombopoiesis occurs from common myeloid progenitor cells in the bone marrow, which differentiate into promegakaryocytes and then into megakaryocytes
Megakaryocytes stay in the bone marrow and produce long processes called proplatelets within their cytoplasm, which are then released in cytoplasmic extensions upon cytokine stimulus
The proplatelets then break up into hundreds of platelets that circulate in the bloodstream, while the remaining nucleus of the ruptured megakaryocyte is phagocytised by macrophages
Megakaryocyte and platelet production is regulated by thrombopoietin, a hormone produced by the liver and kidneys
Thrombopoietin stimulates differentiation of myeloid progenitor cells into megakaryocytes and causes the release of platelets
Thrombopoietin is regulated by negative feedback mechanism, based on the levels of platelets in the blood
Each megakaryocyte produces between 5000 and 10000 platelets before its cellular components are fully depleted
Altogether, around 10^{11} platelets are produced each day in an adult
Average life span of a platelet is 5–10 days
Old platelets are phagocytosed by macrophages in the spleen and liver
Up to 40% of platelets are stored in the spleen as a reserve and are released when needed during injury
Megakaryoblast – 25–50 μm diameter and large kidney-shaped nucleus, with several small nucleoli
Megakaryocyte – giant cells, up to 150 μm diameter, large, irregularly lobulated nuclei and no visible nucleoli. Cytoplasm contains many mitochondria, RER and extensive Golgi
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