How does Follicle Stimulating Hormone (FSH) function in the menstrual cycle?

Sourav PanNovember 12, 2024

Answered

Follicle-Stimulating Hormone (FSH) plays a crucial role in the menstrual cycle, primarily regulating the growth and maturation of ovarian follicles. Here’s a detailed overview of its functions:

Role of FSH in the Menstrual Cycle

1. Follicular Phase Initiation:
   • At the beginning of the menstrual cycle, FSH is secreted by the anterior pituitary gland in response to Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus. This occurs on approximately day 1 of the cycle when estrogen levels are low, signaling the pituitary to produce FSH and Luteinizing Hormone (LH).
2. Follicle Development:
   • FSH stimulates the growth and maturation of ovarian follicles. Each month, several follicles begin to develop, but usually only one becomes dominant and continues to mature while others undergo atresia (degeneration) . FSH acts on granulosa cells within these follicles, promoting their proliferation and the production of aromatase, which converts androgens to estrogen .
3. Estrogen Production:
   • As follicles grow, they produce increasing amounts of estrogen (specifically estradiol). The rising estrogen levels provide feedback to the pituitary gland, leading to a temporary suppression of FSH secretion as the dominant follicle takes over . This negative feedback mechanism ensures that only one follicle matures fully for ovulation.
4. LH Surge and Ovulation:
   • Around day 14 of a typical 28-day cycle, high levels of estrogen from the dominant follicle trigger a surge in LH, which is essential for ovulation—the release of the mature egg from the follicle. FSH also peaks at this time, although its primary role is in follicle maturation rather than directly causing ovulation .
5. Post-Ovulation Phase:
   • After ovulation, FSH levels drop significantly due to increased progesterone from the corpus luteum and negative feedback from estrogen and inhibin produced by the dominant follicle. This reduction prevents further follicular development during the luteal phase .
6. Late Luteal Phase:
   • Towards the end of the menstrual cycle, as progesterone levels decline and inhibin A decreases, FSH levels may rise again slightly in preparation for the next cycle. This increase allows for the recruitment of new follicles for maturation in the subsequent cycle