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Question #45391
The Question
In certain abnormal pregnancies characterized by a polyploid genetic constitution (e.g., triploidy), the trophoblastic tissue proliferates excessively, secreting aberrantly high levels of Human Chorionic Gonadotropin (hCG). Clinically, such patients often exhibit suppressed maternal Thyroid Stimulating Hormone (TSH) levels. Which of the following best explains the molecular basis of this endocrine cross-talk?
Options
- A.
hCG shares structural homology with TSH, specifically an identical alpha-subunit, allowing it to stimulate the maternal thyroid gland and trigger negative feedback on TSH.
- B.
High hCG levels directly inhibit the maternal hypothalamus from releasing Thyrotropin-Releasing Hormone (TRH) through a placental-hypothalamic feedback loop.
- C.
The polyploid placenta produces excessive human Placental Lactogen (hPL), which acts as a competitive inhibitor at maternal TSH receptors.
- D.
Excessive hCG overstimulates the corpus luteum to produce massive amounts of progesterone, which directly suppresses the anterior pituitary thyrotrophs.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Estrogen|Progesterone|Aneuploidy|Placenta
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize placental hormones (hCG, hPL) and pituitary hormones (TSH, LH, FSH) in isolation.
The trap is failing to recognize the evolutionary and structural homology (identical alpha-subunits) among glycoprotein hormones.
When hCG is pathologically high (as in polyploid molar pregnancies), receptor cross-talk occurs, leading to subclinical hyperthyroidism and subsequent TSH suppression via negative feedback.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Human Reproduction - Class 12 |
| Concept | Placental Endocrine Profile |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |