Single Best Answer (SBA) · The Placenta and Fetoplacental Unit
A clinician explains the dual origin of the placenta. Which single statement correctly describes the fetal and maternal contributions?
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Answer: A. The fetal part derives from trophoblast and extraembryonic mesoderm; the maternal part from the endometrium
Dual origin of the placenta
The placenta is a feto-maternal organ with contributions from both fetus and mother.
Contributions
- Fetal part: derived from trophoblast and extraembryonic mesoderm (the chorionic plate).
- Maternal part: derived from the endometrium (decidua basalis).
Development
- Rapid proliferation of trophoblast; the syncytiotrophoblast erodes maternal capillaries so that trophoblast lacunae anastomose with maternal vessels, establishing the intervillous circulation.
- Placental growth is rapid until about 18 weeks.
This dual origin is why the placenta is described as a feto-maternal interface and why it functions as an immunological allograft tolerated by the mother.
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