Bone marrow - nonneoplastic
Normal
Megakaryocytes

Author: Dragos Luca, M.D. (see Authors page)

Revised: 5 July 2017, last major update August 2012

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Bone marrow megakaryocytes [title]

Cite this page: Megakaryocytes. PathologyOutlines.com website. http://pathologyoutlines.com/topic/bonemarrowmegakaryocytematuration.html. Accessed October 22nd, 2017.
Definition / general
  • Progresses from myeloid stem cell (pluripotential hematopoietic stem cell) to megakaryoblast to promegakaryocyte to megakaryocyte to proplatelets (released into circulation) to platelets (J Thromb Haemost 2003;1:1580, Front Biosci 2007;12:2050)
  • Two groups of factors influencing megakaryopoiesis are early acting multilineage cytokines (stem cell factor, GM-CSF, IL3, IL6) and cytokines that are more megakaryocyte specific (thrombopoietin)
  • Thrombopoietin: produced by bone marrow stromal cells, hepatocytes and proximal renal tubular epithelial cells; poorly understood regulation
  • Maturation is characterized by an increase in size and lobulation of nuclei and is controlled by thrombopoietin (J Clin Invest 2005;115:3339)
  • Endomitosis: unique property of megakaryocytes characterized by ongoing DNA synthesis, without mitosis resulting in progressive nuclear lobulation with increasing DNA content (nuclear lobes remain connected)
  • Megakaryocytes form demarcation membrane within cytosol, which leads to production of platelets
  • Maturation is associated with acquisition of surface GP Ib, GP IIb and von Willebrand factor
  • Four types of cytoplasmic granules are alpha, delta, gamma and peroxisomes
  • Megakaryocytes reside next to the bone marrow sinuses and project pseudopodia through the sinus walls, releasing platelets directly into the circulation
Diagrams / tables

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Megakaryopoiesis pathways

Proplatelet formation

Clinical features
  • Megakaryocytes are smaller in fetuses and infants and show less nuclear segmentation when compared to older children
  • Platelet production appears to be dependent on megakaryocyte ploidy
  • Platelet production rate under homeostatic conditions: 2 - 4 x 109/kg/day; may increase 8 - 10x if needed; 10 day survival time in peripheral blood
  • Emperipolesis: other cells, especially neutrophils, pass through megakaryoctye tubular system (due to its location) to enter the circulation
  • Thrombocytopenia with normal / increased megakaryocytes: congenital (Bernard-Soulier, May-Hegglin, gray platelet syndrome) or acquired (ITP, DIC, TTP, HUS, hypersplenism, megaloblastic anemia)
  • Thrombocytopenia with decreased megakaryocytes: congenital (Fanconi, thrombocytopenia with absent radii, X linked amegakaryocytic thrombocytopenia, dyskeratosis congenita, Shwachman-Diamond) or acquired (aplastic anemia, bone marrow infiltration, infections, toxins, immune disorders)
  • Thrombocytosis: congenital (familial essential thrombocythemia, other familial myeloproliferative disorders) or acquired (reactive or neoplastic)
Microscopic (histologic) description
  • Megakaryoblast: variable size (7 - 35 microns); may be designated micromegakaryoblast if < 15 microns; round / ovoid cells with scanty blue agranular cytoplasm that often forms a rim around nucleus and may have a few small budding protrusions at periphery; nuclei are round / oval with coarse granular chromatin, one or more nucleoli
  • Megakaryocyte: randomly disbursed throughout bone marrow; 50 - 150 microns (largest normal nucleated cell in marrow); micromegakaryocytes measure 15 - 30 microns; abundant light blue to pink cytoplasm with numerous purple red or pink granules; nucleus has 8, 16 or 32 overlapping lobes; no nucleolus; megakaryocytes producing platelets may have demarcated granular clumps of platelets streaming from the margins
Microscopic (histologic) images

Images hosted on PathOut server:

Megakaryocytes



Images hosted on other servers:

Megakaryoblasts

Megakaryocytes


Emperipolesis

CD34+ megakaryocytes (figures A, C, D)

CD62P+ megakaryocyte

Endomitosis


Platelet formation

Positive stains
Negative stains
Electron microscopy images

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Platelets