Sex hormone regulation

Sex hormones are substances produced by the sex organs, i.e. they are largely synthesized by the ovaries in females and in the testes in males. Both male and female sex hormones are synthesized from the same precursor, cholesterol.

Male sex hormones such as testosterone help develop and maintain male sexual characteristics and are involved in the production of sperm in the testes. Testosterone is the androgen produced in the testes in specialized cells called Leydig cells. Testosterone production in men declines with aging.

The female sex hormones are estrogen and progesterone, whose main functions are the development and maintenance of female sexual characteristics, as well as being involved in the development of the menstrual cycle, fertility, preparation of the reproductive system for the reception of sperm, and gestation. The most important estrogen synthesized by the ovary is oestradiol, while progesterone is the most important of the gestagen or pregnancy hormones.

The ovarian follicles are the site of estrogen and progesterone production. These hormones are secreted in a cyclical sequence that is repeated approximately every 28 days during a woman's fertile years and is known as the menstrual cycle. From a certain age, between 40 and 60, ovarian function is exhausted, hormone production is reduced, and menstrual cycles cease. This last biological process is known as menopause.

Regulation

The synthesis of sex hormones is controlled by the pituitary gland, a small gland at the base of the brain. This gland synthesizes, among other substances, gonadotropins, which are the testicular-stimulating hormones in males and ovarian-stimulating hormones in females. When a person reaches puberty, there is an increase in the synthesis and release of pituitary gonadotropins. These reach the testicle or ovary where they stimulate the production of sex hormones which, in turn, give rise to the characteristic changes of puberty. In women, gonadotropin secretion is cyclical, giving rise to the cyclical secretion of estrogen and progesterone and to female menstrual cycles.

Importance of genetics

Sex hormone-binding globulin (SHBG) is the key protein that transports testosterone and estrogen into the bloodstream in both men and women. In addition, SHBG helps regulate its effects on different tissues and organs in the body.

In addition to effects on reproduction in men and women through regulation of sex hormones, SHBG has been linked to many chronic diseases such as type 2 diabetes and hormone-sensitive cancers such as breast and prostate cancer.

It is estimated that approximately 50% of the variation in SHBG concentrations in the bloodstream is inherited from parents, suggesting that SHBG levels are under significant genetic control.

Gene or region studied

  • SHBG
  • 17p13.1
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