Fig. 2. The interhaemal barrier in the chorioallantoic placenta, which is regarded to influence the diffusion distance responsible for the oxygen diffusing capacity. (A)
Epitheliochorial placenta with all maternal layers. (B) Endotheliochorial placenta: the trophoblast attached to the endothelium of the maternal capillaries. (C) Haemochorial
placenta: the maternal blood is directly in touch with the trophoblast. 1, endothelium of fetal capillary; 2, fetal connective tissue; 3, chorionic trophoblast; 4, uterine
epithelium; 5, uterine stroma; 6, endothelium of maternal capillary.