When does formation of blood begin during embryonic development?

During embryonic development, the formation of blood, also known as hematopoiesis, begins around week 5. This process starts in the yolk sac and later shifts to the fetal liver and bones as development progresses. By the end of the fifth week, the early blood cells start forming and are crucial for supplying oxygen and nutrients to the developing embryo. Understanding the timeline of embryonic hematopoiesis is critical for cardiovascular perfusionists, as it lays the groundwork for understanding later fetal circulation and the development of the cardiovascular system.