MICROANATOMY

Detailed explanation-1: -Embryonic hematopoiesis begins in the yolk sac and changes to definitive hematopoiesis in the fetal liver. The bone marrow becomes the principal site of hematopoiesis late in gestation.

Detailed explanation-2: -The yolk sac serves as the initial site of erythropoiesis from weeks 3–6 of gestation. The liver functions as the primary site of hematopoiesis from weeks 6–22 of gestation, after which the bone marrow becomes the predominant and lifelong site of blood-cell production.

Detailed explanation-3: -Explanation: Hematopoiesis occurs in the fetal liver and spleen.

Detailed explanation-4: -Primitive hematopoiesis The first wave of blood cell production begins when vascular and hematopoietic cells differentiate from mesodermal progenitors and progressively organize themselves into blood islands in the extra-embryonic yolk sac.