Cell fate is determined by placement in the embryo . HCG is made to contain the corpus luteum and the pregnancy, so the corpus luteum will continue to make progesterone and estrogen, and the uterine lining will continue to thicken. Gastrulation occurs during the second week of development- by day 7, the embryo is partially embedded in the uterine wall. These layers have developmental fates as outlined in p. 308 of the text. Induction is normally the result of an individual cell's placement within the developing embryo V. Organ Development and Development of the Placenta by the third week of development the heart and nervous system begin to form by this time the placenta has begun to form.
Nutrients travel from the mother to the developing child, but blood never passes.
Certain substances such as oxygen and carbon dioxide pass freely, which is key to the health of the developing person. Head growth slows, and the placenta is completed by the tenth week fetal heart beat audible by the fourth month the fifth through the seventh months are dominated by growth. If born, the child can survive at this point, Movement occurs. Head rotates toward the cervix Click here for image 5c on Development.