What is formed first, The placenta or the embryo, could the form simultaneously . For some reason I believe is the placenta . At what point is the umbilical cord formed to attach the embryo to the placenta. ?
The placenta and embryo grow together, through stages of development until delivery. An embryo will eventually grow into a fetus - the placenta in pregnancies where the fetus is fully formed (roughly 24 weeks) is radically different in structure than it is during the embryonic stage of development. The umbilical cord is formed during the fifth week of gestation, or the seventh week of pregnancy. The amniotic sac (zygote) is formed and filled with fluid usually within two weeks of implantation. The placenta follows these same patterns of development - they are inherently more complex in their function, especially after implantation.
Is the amniotic sac (zygote) separate from the placenta ? The sac ( amniotic ) have to be formed early in order to close the entrance from vagina to the uterus, otherwise the fluid will drain .
Trophoblasts form a thin layer along the blastocyst (the sight where the amniotic sac is formed) so yes, they are separate on the microscopic level at this stage. The separation between them grows more and more severe as development continues. An inner and outer layer of membranes in the trophoblast form the zygote and are essential in facilitating the production of early pregnancy hormones. The fluid will not drain unless there is some sort of concentration imbalance. Prenatal fluid is held in the endometrium as the zygote expands to fill the uterus.
