ABSTRACT
In the 5th week the embryonic circulation consists of a primitive heart, and patterns of arterial distribution and venous drainage differing radically from the cardio vascular system of the fetus.
EM BRYON IC BLO O D This differs from both fetal and postnatal blood. Embryonic red blood corpuscles are nucleated. The oxy gen dissociation curve of embryonic hemoglobin (Hb.E) is shifted to the left of the curves for fetal (Hb.F) and postnatal (Hb) hemoglobins (see Chapter 34, Figure 3). Embryonic blood forms extra-osseously, in the yolk sac and chorion, and then the liver, spleen, urogenital ridges, and adrenal glands.
