Detailed definition
The HPO axis is a feedback control system: the hypothalamus pulses GnRH to the pituitary, which releases FSH and LH; FSH and LH stimulate the ovary to develop follicles, ovulate, and produce estradiol and progesterone; the ovarian steroids feed back on hypothalamus and pituitary to modulate GnRH and gonadotropin release. The negative feedback dominates most of the cycle; the positive feedback estradiol surge mid-cycle drives the LH surge that triggers ovulation. As ovarian reserve declines through perimenopause, the ovary produces less inhibin B and estradiol, removing negative feedback and elevating FSH. By menopause, ovarian function is essentially absent and the axis runs with persistently high gonadotropins and minimal ovarian steroids.
Why it matters in menopause
Recognizing menopause as ovarian failure rather than a hypothalamic or pituitary problem clarifies why hormone replacement, not gonadotropin replacement, is the appropriate intervention.
Related terms
Sources
External references: Wikipedia.