HPG Axis (Hypothalamic–Pituitary–Gonadal Axis)
Also known as: HPG · hypothalamic-pituitary-gonadal axis · reproductive axis · HPTA
The hormone loop from hypothalamus (GnRH) to pituitary (LH, FSH) to gonads (testosterone, oestradiol, sperm or eggs).
The hypothalamus releases GnRH in pulses; the pituitary answers with LH and FSH; the testes or ovaries respond with sex hormones and gametes. Those hormones feed back on the brain, so the loop self-regulates.
Kisspeptin sits above GnRH and switches the axis on at puberty. External hormones switch it down, which is why the axis is central to fertility research.
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RELATED TERMS
Luteinising Hormone (LH)
The pituitary hormone that tells the testes to make testosterone and triggers ovulation in women.
Follicle-Stimulating Hormone (FSH)
The pituitary hormone that grows ovarian follicles and supports sperm development in the testes.
Spermatogenesis
The roughly three-month process by which the testes produce mature sperm, driven by FSH and high testosterone inside the testes.
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