OBJECTIVE: To review the process of blood-cell formation in the murine and human yolk
sac. DATA SOURCES: Most articles were selected from the PubMed database. DATA
SYNTHESIS: The yolk sac is the first site of blood-cell production during murine and human
ontogeny. Primitive erythroid cells originate in the yolk sac and complete their maturation,
including enucleation, in the bloodstream. Though species differences exist, the pattern of
hematopoietic progenitor cell emergence in the yolk sac is similar in mouse and man. In …