Bone marrow - nonneoplastic
Embryonic development

Author: Nat Pernick, M.D. (see Authors page)

Revised: 29 June 2017, last major update December 2006

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

PubMed Search: Embryonic development [title] bone marrow

Cite this page: Embryonic development. website. Accessed October 24th, 2018.
Definition / general
  • In embryo, hematopoiesis (other than lymphoid) occurs in yolk sac with formation of mesenchymal derived primitive erythroblasts
  • Aorta also contributes lymphomyeloid stem cells, as do embryonic liver and bone marrow (Development 2002;129:4147, Ann N Y Acad Sci 2005;1044:41)
  • At weeks 10 to 24, liver is primary hematopoietic organ with production of granulocytes and megakaryocytes in sinusoids
  • At months 4 - 5, bone marrow hematopoiesis begins
  • By birth, liver and spleen have minimal role in myelopoiesis and bone marrow is major site of hematopoiesis
Diagrams / tables

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Blood islands in embryo

Microscopic (histologic) images

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Yolk sac at 18 days

Fetal liver at 17 weeks

Fetal bone marrow at 19 weeks