Describe the hormonal regulation of the menstrual cycle, indicating the role of the hypothalamus, pituitary gland, ovary and the feedback mechanisms in both the follicular and luteal phases.
Answer
The menstrual cycle is regulated by GnRH from the hypothalamus stimulating FSH and LH release from the pituitary; FSH promotes follicular growth and estrogen secretion, which initially provides positive feedback leading to the LH surge that triggers ovulation; after ovulation, the corpus luteum secretes progesterone (and some estrogen) which exerts negative feedback on GnRH, FSH and LH, maintaining the endometrium during the luteal phase.
Step-by-step solution
- State that the hypothalamus releases GnRH in a pulsatile manner, which acts on the anterior pituitary.
- Explain that GnRH induces the pituitary to secrete FSH and LH.
- Describe the follicular phase: FSH stimulates several ovarian follicles; growing follicles secrete estrogen, which initially exerts negative feedback but later positive feedback to produce the LH surge.
- Mention that the LH surge causes ovulation and formation of the corpus luteum.
- During the luteal phase, the corpus luteum secretes progesterone (and some estrogen).
- Explain that high progesterone levels provide negative feedback to the hypothalamus and pituitary, suppressing further GnRH, FSH and LH release until the cycle ends or pregnancy occurs.
Common mistake: Leaving out the negative feedback of progesterone in the luteal phase
Concept tested: Hormonal control of menstrual cycle
Published · How this solution was prepared and checked
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