LH surge triggers ovulation in females. The LH surge is triggered by high estrogen levels through which mechanism?
- A Negative feedback of estrogen on the pituitary causing FSH release
- B Progesterone-induced sensitization of LH receptors
- C Positive feedback of sustained high estrogen on hypothalamic GnRH and pituitary LH secretion ✓
- D Inhibin-B withdrawal from the dominant follicle
Correct answer: C. Positive feedback of sustained high estrogen on hypothalamic GnRH and pituitary LH secretion
Explanation
In the periovulatory phase, rising estradiol from the dominant follicle exceeds a threshold (~200 pg/mL for >36 hours). This high sustained estrogen switches from exerting negative feedback to positive feedback on both hypothalamic GnRH pulse frequency and pituitary LH responsiveness, producing the midcycle LH surge. This surge triggers the oocyte's resumption of meiosis and final follicular rupture approximately 36-40 hours later. Progesterone amplifies but does not initiate the LH surge.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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