What is the location of hematopoiesis during embryonic development?

During embryonic development, hematopoiesis occurs in a series of locations as the organism grows. Initially, hematopoiesis takes place in the yolk sac, which provides the early embryonic blood cells necessary for initial development. As the embryo continues to grow, the liver becomes the predominant site of hematopoiesis, taking over from the yolk sac. This phase is crucial as the liver supports the substantial need for red blood cells and other blood components during the later stages of fetal development. Finally, as the fetus matures and approaches the later stages of development and birth, the bone marrow becomes the primary site of hematopoiesis and continues to be the main site throughout life.

This sequence of hematopoietic locations—yolk sac, liver, and then bone marrow—reflects the shifting needs and capabilities of the developing organism. The other options focus on one specific location, which does not capture the dynamic nature of hematopoiesis during these critical stages of development.