Placental bed blood circulation through;
A. Villi
B. Spiral arteries
C. Chorionic membrane
D. Umbilical artery
Correct Answer: B. Spiral arteries
Explanation
The placental bed blood circulation refers to how maternal blood reaches the placenta and interacts with the fetal circulation. Here’s a detailed explanation:
1. Maternal Side Circulation
- Spiral arteries: Maternal blood enters the intervillous space of the placenta primarily through the spiral arteries of the endometrium (maternal uterine lining).
- These arteries spiral through the decidua and open into the intervillous space, bathing the chorionic villi with maternal blood.
- This allows nutrient and gas exchange between maternal and fetal blood.
- Intervillous space:
- The maternal blood fills this space and comes in close contact with the chorionic villi, which contain fetal capillaries.
- After delivering oxygen and nutrients, maternal blood drains via endometrial veins back to the maternal circulation.
2. Fetal Side Circulation
- Umbilical arteries (2 in number):
- Carry deoxygenated fetal blood from the fetus to the placenta.
- They branch into smaller vessels in the chorionic villi, forming a network of capillaries.
- Chorionic villi:
- Act as the functional unit where maternal-fetal exchange occurs.
- Oxygen and nutrients from maternal blood diffuse into fetal capillaries, while fetal waste (like CO₂) diffuses into maternal blood.
- Umbilical vein (1 in number):
- Returns oxygenated and nutrient-rich blood from the placenta to the fetus.
3. Key Points
- There is no direct mixing of maternal and fetal blood; exchange occurs via diffusion across the placental barrier.
- Maternal blood flow through the spiral arteries is crucial; inadequate remodeling of these arteries can lead to conditions like preeclampsia.
- The fetal circulation through the umbilical vessels ensures continuous delivery of oxygen and nutrients to the developing fetus.
✅ Summary Diagram (Verbal):Maternal spiral arteries → Intervillous space → Fetal capillaries in chorionic villi Fetal blood: Umbilical arteries → Chorionic villi capillaries → Umbilical vein → Fetus
If you want, I can make a simple labeled diagram of placental circulation that shows both maternal and fetal blood flow—it makes this concept much easier to visualize. Do you want me to do that?
Other Options Details
Here is a clear description of all the options related to the placenta and fetal circulation:
A. Villi (Chorionic villi)
- Finger-like projections arising from the chorion.
- They contain fetal capillaries.
- Main functional unit of the placenta.
- Responsible for exchange of oxygen, nutrients, and waste products between maternal and fetal blood.
- Do not mix maternal and fetal blood directly.
B. Spiral arteries
- Maternal blood vessels arising from the uterine arteries.
- Open into the intervillous space of the placenta.
- Supply oxygenated maternal blood to bathe the chorionic villi.
- Essential for adequate placental perfusion.
- Abnormal spiral arteries are associated with conditions like preeclampsia and IUGR.
C. Chorionic membrane
- One of the fetal membranes, formed by the chorion.
- Lies between the amnion and decidua.
- Contributes to formation of the placenta and chorionic villi.
- Provides structural support and protection to the fetus.
- Plays a role in early placental development.
D. Umbilical artery
- Usually two umbilical arteries are present in the umbilical cord.
- Carry deoxygenated blood and waste products from the fetus to the placenta.
- Branch from the fetal internal iliac arteries.
- Important for fetal circulation.
- Absence of one artery (single umbilical artery) may be associated with congenital anomalies.
Summary Table
Structure Origin Function Villi Fetal (chorion) Exchange of gases & nutrients Spiral arteries Maternal Supply maternal blood Chorionic membrane Fetal Protection & placental formation Umbilical artery Fetal Carries deoxygenated blood
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Writer: Vandita Singh, Lucknow (GS India Nursing Group