Primary site of hematopoiesis in the fetus | Crack AIIMS, AIPG NOV 2016 MCQs

Which organ is the primary site of hematopoiesis in the fetus before mid pregnancy? 

A. Bone 
B. Liver 
C. Spleen 
D. Lung

Answer.B. (Liver) Fetal Hematopoiesis

·         Begins in the yolk sac (2 -8 weeks) - progenitor cells migrate from the yolk sac to the liver at 5-8 weeks gestation Only terminal differentiation of red cells occurs in the yolk sac

·         Liver active from 5-8 weeks gestation - mainly red cells. Spleen also involved before 20 weeks

·         Begins in the medullary cavity of the clavicle at about 10-12 weeks and in the medullary cavity of long of bones at - 20 weeks gestation

·         Some lymphocytes are produced in lymph nodes