Which hormones are produced by the ovaries during the menstrual cycle? Select all that apply.

Estrogen, specifically estradiol (E2), plays a dual role in the hypothalamic-pituitary-ovarian axis through both negative and positive feedback mechanisms. During the late follicular phase, when estradiol levels remain consistently high—typically >200 pg/mL for at least 50 hours—the feedback on the hypothalamus and anterior pituitary shifts from negative to positive. This stimulates a GnRH surge, which triggers a massive LH release (LH surge), leading to ovulation. The LH surge also initiates the transformation of the ruptured follicle into the corpus luteum.

Rationale for correct answer

C. Estrogen at sustained high levels switches to positive feedback, stimulating GnRH and causing the LH surge. This is the critical hormonal trigger for ovulation around day 14 of a typical 28-day cycle.

Rationale for incorrect answers

A. Progesterone exerts only negative feedback on GnRH, FSH, and LH throughout the cycle, especially during the luteal phase. It does not cause the LH surge and actually prevents further ovulation.

B. FSH is regulated by negative feedback via estrogen and inhibin. It does not trigger the LH surge and is not part of the positive feedback loop leading to ovulation.

D. Inhibin is secreted by granulosa cells and specifically suppresses FSH release via negative feedback. It plays no role in triggering the LH surge or stimulating GnRH.

Take home points

• High sustained estrogen levels trigger positive feedback on GnRH and LH.
• The LH surge causes ovulation and luteinization of the follicle.
• Progesterone and inhibin exert negative feedback and suppress further ovulation.
• FSH supports follicle growth but is not involved in the LH surge trigger.

hCG is a glycoprotein hormone secreted by the trophoblast cells of the developing embryo shortly after implantation, typically detectable in maternal serum by day 8–10 post-ovulation. Its primary role is to rescue the corpus luteum, preventing its degeneration and allowing continued secretion of progesterone and estrogen. These hormones maintain the decidualized endometrium, preventing menstruation and supporting early pregnancy. hCG shares structural similarity with LH and binds to LH receptors on the corpus luteum. Peak serum hCG levels reach 100,000–200,000 mIU/mL by 10 weeks gestation.

Rationale for correct answer

C. hCG prevents luteolysis by acting on LH receptors of the corpus luteum, maintaining its progesterone production. This sustains the endometrial lining for implantation and early embryonic development.

Rationale for incorrect answers

A. hCG does not stimulate new follicle development. In fact, high progesterone and estrogen levels maintained by the corpus luteum inhibit FSH, preventing new folliculogenesis during early pregnancy.

B. hCG prevents menstruation by maintaining the corpus luteum and its hormone output. Menstruation is triggered by progesterone withdrawal, which hCG directly prevents.

D. hCG supports the continued production of progesterone, not its inhibition. It ensures the endometrial lining remains intact until the placenta takes over hormone production around week 10–12.

Take home points

• hCG maintains the corpus luteum during early pregnancy.
• It prevents menstruation by supporting progesterone production.
• hCG mimics LH and binds to LH receptors on luteal cells.
• It does not promote follicle development or suppress progesterone.