Maternal blood Uterine artery supply in Chorionic villi and vein intervillus space Placenta Yolk sack Amniotic fluid Uterus Uterus Chorion Umbilical cord Amnion Umbilical Umbilical Placenta vein artery 形成胎盘，建立母胎循环 形成胎盘，建立母胎循环