Question

How is the placenta formed? Write its function.

Answer 1

Hint: Baby inside a mammal needs nutrients and oxygen to survive and develop. It needs protection from the environment and sudden movements. It needs immunity from the microbes in the maternal body and surroundings. The fetus needs to be attached to a particular place throughout the time.

Complete answer:
Placenta is a circular organ in the uterus of a pregnant mammal. It nourishes the foetus through the umbilical cord throughout the pregnancy. It is a temporary organ.

The placenta starts to develop when the fertilized egg called blastocyst implants in the maternal endometrium. The outer layer of this blastocyst forms the placenta. This layer has two further layers- underlying cytotrophoblast and overlying syncytiotrophoblast. The latter has a multinucleated cell layer that covers the placenta. It is formed after the differentiation and fusion of the cytotrophoblast cells. The syncytiotrophoblast acts as the barrier which is the main function of the placenta.

The placenta grows throughout the pregnancy. Maternal blood supply cells to the placenta and is completed by the end of the first trimester.
Functions:-
- It has a major function of providing nutrition and gas exchange. The perfusion of intervillous spaces of the placenta with the mother’s blood allows the transfer. It can be an active or passive process.
- Waste products from the fetus are expelled via the placenta. It is diffused to the maternal blood.
- It gives protection to the fetus. It provides passive immunity to the fetus.
- It acts as a barrier between the mother’s body and fetus to pass any microbe from the maternal body to the fetus.
- Placenta releases HCG (human chorionic gonadotropin) hormone which ceases the menstrual cycle of the mammal during the pregnancy.
- It also acts as a reservoir of blood for the fetus.

Note: Placental expulsion at the time of birth is a physiological separation of the placenta from the walls of the uterus. It takes about 20-30 min after birth. It can be managed by giving oxytocin via injection. It can also happen itself. Blood loss or bleeding may be reduced by using oxytocin.