title: Early origins of definitive erythroid cells in the chick embryo.
abstract: The early maturation stages of definitive erythroid cells are observed in the embryonic circulation of the chick yolk sac at 4.5--5 days of incubation. Light and electron microscope observation of the mesoderm of the yold sac membrane indicate that individual presumptive precursors of the definitive-line are present as early as 2 days of incubation and give rise to sequestered populations of immature erythroblasts within sinusoids during the period of 2.5-6 days incubation. Such isolated populations of definitive-line erythroblasts eventually connect with the established capillary circulation of yolk sac membrane but a large proportion of the erythroblasts temporarily remain associated with the endothelium prior to free circulation.
mesh_terms: D000818:Animals; D002196:Capillaries / Q000196:embryology; D002642:Chick Embryo; D004900:Erythroblasts / Q000166:cytology*; D004912:Erythrocytes / Q000166:cytology*; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D008648:Mesoderm / Q000166:cytology*; D013997:Time Factors; D015017:Yolk Sac / Q000098:blood supply / Q000166:cytology* / Q000648:ultrastructure