Question

Explain the formation of placenta after implantation in a human female.

Answer 1

Hint: Placenta is a defining characteristic of placental mammals. It is present only during the development of the foetus which means It is developed only during the time of pregnancy.. Placenta provides nutrients to the growing foetus.

Complete answer: The placenta is a temporary organ. The placenta is attached to the wall of the uterus ( uterine wall ) and baby’s umbilical cord which arises from it. It is a special tissue formed by two sets of villi. One set of villi is given by a wall of the uterus and another set arises from the embryo. The placenta begins to develop upon implantation of a blastocyst which occurs in the maternal endometrium. The blastocysts have two different cell types; they have outer trophoblast cells and inner cell mass. These trophoblast cells develop to form the placenta, while the inner cell mass forms the foetus and foetal membrane. The placenta is formed by 18 – 20 weeks and continues to grow throughout the pregnancy. It has a length of about 22 cm and a width of about 2.5 cm. By the 12 weeks, the placenta is formed and ready to help the foetus with the nourishment. It allows in the uptake of nutrients, eliminates waste, aids in thermoregulation and gases exchange. Antibodies like IgG can pass through the human placenta and later it protects the foetus in the uterus. Placenta also performs the endocrine function, i.e. they release few hormones which are needed for the growth of sex organs.

Note: Human placenta has a chorioallantoic placenta, i.e. it is formed from the chorion and allantois. The mother body may consider the foetus as a foreign body, but the placenta protects the foetus from the normal immune response by releasing antibodies.