<P> The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium . The outer layer of the blastocyst becomes the trophoblast , which forms the outer layer of the placenta . This outer layer is divided into two further layers : the underlying cytotrophoblast layer and the overlying syncytiotrophoblast layer . The syncytiotrophoblast is a multinucleated continuous cell layer that covers the surface of the placenta . It forms as a result of differentiation and fusion of the underlying cytotrophoblast cells , a process that continues throughout placental development . The syncytiotrophoblast ( otherwise known as syncytium ) , thereby contributes to the barrier function of the placenta . </P>
<P> The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium . The outer layer of the blastocyst becomes the trophoblast , which forms the outer layer of the placenta . This outer layer is divided into two further layers : the underlying cytotrophoblast layer and the overlying syncytiotrophoblast layer . The syncytiotrophoblast is a multinucleated continuous cell layer that covers the surface of the placenta . It forms as a result of differentiation and fusion of the underlying cytotrophoblast cells , a process that continues throughout placental development . The syncytiotrophoblast ( otherwise known as syncytium ) , thereby contributes to the barrier function of the placenta . </P>
placenta develops from the outer cells of the
placenta develops from the outer cells of the
trophoblast
trophoblast