Gonadotropinachse

The gonadotropin axis, also known as the hypothalamic-pituitary-gonadal axis or HPG axis, is a complex system that regulates reproduction and sexual development in vertebrates. It involves the coordinated action of the hypothalamus, the pituitary gland, and the gonads (testes in males and ovaries in females). The hypothalamus, located in the brain, releases gonadotropin-releasing hormone (GnRH). GnRH then travels to the pituitary gland, a small gland at the base of the brain, stimulating it to produce and release two key hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones are called gonadotropins because they act on the gonads.

LH and FSH travel through the bloodstream to the testes and ovaries. In males, FSH stimulates sperm production (spermatogenesis), while LH triggers the production of testosterone, the primary male sex hormone, by Leydig cells. Testosterone is crucial for the development of male secondary sexual characteristics and the maintenance of reproductive function. In females, FSH stimulates the growth and maturation of ovarian follicles, which contain the eggs. As follicles develop, they produce estrogen. LH plays a critical role in ovulation, the release of a mature egg from the ovary, and also stimulates the corpus luteum, a temporary endocrine structure that produces progesterone, which is essential for preparing the uterus for pregnancy.

The HPG axis operates under a negative feedback system. High levels of sex hormones, such as testosterone and estrogen, signal back to the hypothalamus and pituitary gland, inhibiting the release of GnRH, LH, and FSH. Conversely, low levels of sex hormones stimulate the release of these hormones. This intricate feedback loop ensures that hormone production is maintained within appropriate ranges for normal physiological function. Disruptions to the gonadotropin axis can lead to various reproductive issues, including infertility, irregular menstrual cycles, and problems with sexual development.