Question

When and how does placenta develop in human females?

Answer 1

Hint: While all placentae in mammals have the same functions, in various classes of mammals there are major variations in form and function. Human, bovine, equine and canine placentae, for example, are very distinct at both gross and microscopic stages. The ability of these species' placentae to supply maternal immunoglobulins to the fetus also varies.

Complete answer:
The placenta is an endocrine organ discovered during conception in animals during fetal development. The chorionic villi and the uterine tissue interdigitate with each other after around 12 weeks of pregnancy and together form a structural and functional unit called the placenta between the developing embryo (foetus) and the maternal body. At this point, a tough cord called the umbilical cord that connects the embryo to the uterus from the placenta is also developed. The placenta brings the fetus nutrients and assists in the mixing of gases.

Mammalian placentas evolved about 150 million to 200 million years ago. The protein syncytin, present between mother and baby in the outer placenta barrier (syncytiotrophoblast), has a certain RNA signature in its genome that has contributed to the belief that it evolved from an ancient retrovirus: basically, a 'healthy' virus that helped pave the transition from egg-laying to live-birth.

Note: The human placenta will be transferred by IgG antibodies, thereby shielding the fetus in utero. This antibody transmission occurs as early as the 20th week of gestational age, and definitely by the 24th week. This passive immunity lasts for several months after birth, thereby supplying a carbon copy of the long-term humoral immunity of the mother to the newborn to see the child through the critical first months of extrauterine life. However, IgM does not reach the placenta, which is why certain pregnancy-acquired diseases can be harmful for the fetus.