Fetal hemopoiesis first occurs in :
Ans. is a i.e. Yolk sac In the very early embryo, hemopoiesis is first demonstrable in the yolk sac. (It begins between the 10th" to 14th day of gestation, k/a mesoblastic period). The next major site is the dvei (Begins by 6-8 weeks of gestation and completely replaces yolk sac by 10-12 weeks and remain predominant till 20-24 weeks called as hepatic punuu of heinopoeiss) followed by the bone marrow (It stas taking over the liver by the second trimester called as myeloid period Erythropoiesis is regulated primarily by erythropoietin which increases along with gestational age. Extra Edge When hemopoiesis occurs in yolk sac - Hemoglobins Gower I, Gower 2 and Poland are made. Erythropoiesis in the liver, produces hemoglobin F Finally when hemopoiesis moves to bone marrow, normal hemoglobin A appears in fetal red cells and is present in progressively greater amounts as the fetus matures After 8th gestational week HbF is the predominant Hb. At 24 weeks of gestation it constitutes 90% of the fetal hemoglobin. At bih HbF is 70% of total hemoglobin and HbA is 30%. At bih HbA2 is less than 1% is seen but by 12 month of age the normal level of 2.0-3-4% is attained. Throughout life, the normal ratio of HbA to A. is about 30 : 1. Clotting factors in fetus : Fetal fibrinogen appears as early as 5 weeks of gestation. All the rest clotting factors are produced by 12 weeks of gestation. Factors low in cord blood are : Factor II, VII, IX, X, XI, XII, XIII and fibrinogens. Without prophylactic vitamin K treatment at bih. vitamin K dependant coagulation factors fuher decrease during the first few days of life and may lead to hemorrhage in newborn.
Yolk sac
Liver
Spleen
Bone marrow