If placenta begins to formed by 6 Weeks , then how fetoplacental circulation is established by day 21 after fertilization?

The timeline you’ve mentioned seems to be inaccurate. Placental formation is a complex process that occurs over several weeks, and fetoplacental circulation is established as part of this process. Here’s a more accurate timeline:

  1. Fertilization (Day 0-1): Fertilization occurs when a sperm fertilizes an egg, forming a zygote. This marks the beginning of embryonic development.
  2. Blastocyst Formation (Day 5-6): The fertilized egg undergoes multiple cell divisions and forms a blastocyst, a fluid-filled structure with an inner cell mass that will become the embryo.
  3. Implantation (Day 6-10): The blastocyst attaches to the uterine wall and begins to implant. This marks the initial stages of placental development.
  4. Placental Development (Weeks 3-12): The placenta starts to form during the third week after fertilization. Specialized cells from both the embryonic tissue and the uterine lining contribute to the development of the placenta. Blood vessels from both the embryo and the mother begin to grow and interact.
  5. Fetoplacental Circulation (Weeks 4-5 onwards): As the placenta develops, blood vessels from the developing embryo come into close proximity with the maternal blood vessels within the placenta. This allows for the exchange of nutrients, gases, and waste products between the mother’s blood and the embryonic circulation. The circulatory system of the embryo develops and connects to the placental vessels, establishing the fetoplacental circulation.

By day 21 after fertilization, the embryonic development is still in its early stages, and the formation of the placenta and establishment of fetoplacental circulation have not yet occurred. These processes occur over several weeks as the embryo develops and the placenta matures.

It’s important to rely on accurate and reputable sources for information on embryonic and fetal development. If you have questions about this topic, it’s always a good idea to consult with a medical professional or trusted educational resources.