Hypothalamic–pituitary–gonadal axis

The hypothalamic–pituitary–gonadal axis is a hormonal signaling system linking the hypothalamus, pituitary gland, and gonads to regulate reproductive development, function, and hormone production.

Gonadotropin-releasing hormone: A hypothalamic peptide hormone that stimulates pituitary release of luteinizing hormone and follicle-stimulating hormone. Pulsatile release of this hormone initiates the axis’s pituitary signaling.
Hypothalamus: A brain region that coordinates endocrine, autonomic, and homeostatic functions. Its neurons generate the releasing signals that start the axis.
Gonadotropin-releasing hormone stimulation test: A diagnostic test that measures pituitary gonadotropin responses after gonadotropin-releasing hormone or an analogue is given. The response helps assess pituitary capacity within the signaling chain.
Puberty: The developmental transition in which reproductive organs mature and secondary sexual characteristics emerge. Axis reactivation drives the hormonal changes that initiate reproductive maturation.
Neurokinin B: A neuropeptide that participates in hypothalamic regulation of gonadotropin-releasing hormone pulses. Its interaction with kisspeptin and dynorphin helps explain pulse generation.
Luteinizing hormone: A pituitary glycoprotein hormone that regulates ovulation, corpus luteum function, and gonadal steroid production. It carries pituitary signals to gonads and helps control sex-steroid production.
Pituitary gland: An endocrine gland beneath the brain that releases hormones under hypothalamic control. Its anterior lobe relays hypothalamic signals to the gonads.
GnRH agonist: A drug that activates gonadotropin-releasing hormone receptors, often suppressing gonadotropins after continuous exposure. Continuous exposure reverses the effect of the axis’s normal pulsatile GnRH signal.
Menstrual cycle: A recurring sequence of ovarian and uterine changes that prepares the body for possible pregnancy. Cyclic pituitary and ovarian signals coordinate its phases.
KNDy neuron: A hypothalamic neuron expressing kisspeptin, neurokinin B, and dynorphin, involved in reproductive hormone pulse regulation. These neurons are a leading model for how rhythmic GnRH output is generated.

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