Gonadotrophins-luteinizing hormone and follicle stimulating hormone

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hypothalamo-pituitary axis structure and development
functions of the hypothalamo-pituitary axis
anterior pituitary hormones
posterior pituitary hormones
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Regulation of gonadal function by LH & FSH
The hypothalamo-pituitary-gonadal axis is different in males and females.

In females GnRH is secreted from the hypothalamus in a cyclical way leading to a cyclical secretion of LH and FSH from the pituitary, which maintains the menstrual cycle.

  • LH acts on the ovarian follicle and it induces ovulation and maintains the corpus luteum.
  • FSH causes development of the ovarian follicle and stimulates secretion of oestradiol and progesterone.
  • The sex steroids feed back to inhibit release of GnRH and therefore LH and FSH. At sustained high levels however, oestradiol causes a sharp increase in LH secretion linked to ovulation. This is an example of positive feedback.

In males GnRH causes the release of LH and FSH from the anterior pituitary, as in females.

  • LH acts on the Leydig cells of the testes to produce testosterone.
  • FSH acts on the Sertoli cells of the testes to maintain spermatogenesis as well as production of sex-hormone binding globulin.

In males and females FSH stimulates the production of inhibin, which has a negative feedback effect on the hypothalamus and pituitary.

What can go wrong

Insufficient GnRH causes a fall in gonadotrophin production, which leads to amenorrhoea, due to lack of ovulation, in women and impotence and infertility in men. This is sometimes seen when nutrient intake is too low, as in anorexia nervosa, or when excessive exercise is undertaken. It may also be due to a prolactin secreting tumour because prolactin has effects on the hypothalamo-pituitary-gonadal axis. The problems caused by lack of GnRH may be treated by administration of GnRH, gonadotrophins such as recombinant FSH, or sex steroids.