Outer most membrane of placenta is called:
A. Amnion
B. Yolk sac
C. Chorion
D. Meningitis
Correct Answer: C. Chorion
Explanation
Outer most membrane of placenta: Chorion
Explanation:
The placenta is covered by fetal membranes, which are mainly:
- Amnion
- Chorion
- Chorion is the outermost fetal membrane of the placenta.
- It is derived from the trophoblast and extra-embryonic mesoderm.
- The chorion forms chorionic villi, which are responsible for maternal–fetal exchange of gases, nutrients, and wastes.
- The chorion lies outside the amnion and is in contact with the maternal decidua.
Why not the others?
- Amnion → Innermost membrane, surrounds the fetus and amniotic fluid.
- Yolk sac / Allantois → Early embryonic structures, not placental membranes.
✔ Correct answer:
Chorion
Other Options Details
Here is a clear explanation of all the given options, commonly asked in obstetrics and embryology:
A. Amnion
- The amnion is the innermost fetal membrane.
- It forms the amniotic sac, which contains amniotic fluid.
- Functions:
- Protects the fetus from mechanical injury
- Allows free fetal movement
- Maintains constant temperature
- Prevents adhesion of fetus to membranes
- It surrounds the fetus throughout pregnancy.
B. Yolk Sac
- The yolk sac is the first extra-embryonic structure formed during early development.
- Functions:
- Provides early nutrition to the embryo
- Site of early blood cell formation (hematopoiesis)
- Contributes to formation of the primitive gut
- It becomes smaller as the placenta develops and usually disappears later in pregnancy.
C. Chorion
- The chorion is the outermost fetal membrane.
- It is formed from trophoblast and extra-embryonic mesoderm.
- Functions:
- Forms chorionic villi, which participate in placenta formation
- Plays a key role in maternal–fetal exchange
- The placenta develops mainly from the chorion frondosum.
D. Meningitis
- Meningitis is NOT a fetal membrane.
- It is a medical condition, defined as inflammation of the meninges (protective coverings of the brain and spinal cord).
- Causes:
- Bacterial, viral, fungal, or parasitic infections
- Symptoms:
- Fever, headache, neck stiffness, altered consciousness
- Included here as a non-related option compared to fetal membranes.
✅ Key Point
- Amnion, yolk sac, and chorion are fetal/extra-embryonic membranes.
- Meningitis is a disease, not a fetal structure.
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Writer: Vandita Singh, Lucknow (GS India Nursing Group