Placenta takes over function of corpus luteum for production of hormone at:
First, I need to recall the core concept here. The corpus luteum produces progesterone during early pregnancy. But as the pregnancy progresses, the placenta starts taking over this function. The key point is the timing when this transition happens. I remember that around the 8th to 10th week of gestation, the placenta becomes the main source of progesterone. Before that, the corpus luteum is responsible. So the question is likely asking for the timeframe when the placenta takes over.
Now, the correct answer is option C. Let's say the options are different timeframes. The correct answer would be around 8-10 weeks. I need to explain why that's the case. The placenta starts producing enough progesterone by the 10th week, which is crucial for maintaining the pregnancy. The corpus luteum is maintained by hCG from the placenta until then. Once the placenta can take over, the corpus luteum regresses.
For the incorrect options, if other options are earlier (like 6 weeks) or later (like 16 weeks), they would be wrong. For example, at 6 weeks, the corpus luteum is still the main source. At 16 weeks, the placenta is definitely taking over, so that's too late. Another option might be 4 weeks, which is way too early. Each incorrect option needs a brief explanation of why it's not the right timeframe.
The clinical pearl here is that the transition happens in the first trimester, around 8-10 weeks. If a student forgets this, they might confuse it with other hormonal shifts, like hCG peaks earlier. Also, understanding that hCG supports the corpus luteum initially is key. So the high-yield fact is the 8-10 week timeframe for placental takeover.
**Core Concept**
The corpus luteum produces progesterone during early pregnancy until the placenta becomes the primary source. This transition occurs **after the placenta develops sufficient hormone-producing capacity** to sustain the pregnancy. Progesterone is critical for maintaining the endometrium and preventing uterine contractions.
**Why the Correct Answer is Right**
The placenta takes over progesterone production from the corpus luteum by **10–12 weeks of gestation**. Before this, human chorionic gonadotropin (hCG) from the developing placenta sustains the corpus luteum. By the 10th week, the placenta synthesizes progesterone via the **17α-hydroxylation pathway** in its syncytiotrophoblast cells, rendering the corpus luteum obsolete. This ensures continuous progesterone supply for pregnancy maintenance.
**Why Each Wrong Option is Incorrect**
**Option A:** Suggests an earlier timeframe (e.g., 6 weeks), but the corpus luteum remains functional and is still the primary progesterone source at this stage.
**Option B:** Implies a later timeframe (e.g., 16 weeks), but placental progesterone production is fully established