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Follicle stimulating hormone

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Follicle stimulating hormone is produced by the pituitary gland. It regulates the functions of both the ovaries and testes. Lack or insufficiency of it can cause infertility or subfertility both in men and women.

Alternative names for follicle stimulating hormone

FSH; follitropin (pharmaceutical preparations).

What is follicle stimulating hormone?

Follicle stimulating hormone is one of the hormones essential to pubertal development and function of the gonads (ovaries and testes) both in women and men.  It is secreted from the anterior pituitary gland into the bloodstream.  In women, follicle stimulating hormone stimulates the growth of ovarian follicles in the ovary before the release of an egg at ovulation, and promotes oestradiol production.  In men, follicle stimulating hormone acts on the Sertoli cells of the testes to promote sperm production (spermatogenesis). 

How is follicle stimulating hormone controlled?  

The production and release of follicle stimulating hormone is regulated by the levels of a number of circulating hormones released by the ovaries and testes. This system is called the hypothalamic-pituitary-gonadal axis.

In women, when hormone levels fall towards the end of the menstrual cycle, this is sensed by nerve cells in the hypothalamus.  These cells produce more gonadotrophin-releasing hormone which in turn stimulates the pituitary gland to produce more follicle stimulating hormone and luteinising hormone and release these into the bloodstream.   The rise in follicle stimulating hormone stimulates the growth of the follicle in the ovary.  With this growth, the cells of the follicles produce increasing amount of oestradiol and inhibin.  In turn, the production of these hormones is sensed by the hypothalamus (or pituitary gland in the case of inhibin) and less gonadotrophin-releasing hormone and follicle stimulating hormone will be released.  However, as the follicle matures, there is a surge in oestradiol production which switches the feedback mechanisms in the brain from negative to positive feedback, causing more gonadotrophin-releasing hormone, follicle stimulating hormone and luteinising hormone to be released.  This peak in hormone levels eventually leads to ovulation.

Thus, during each menstrual cycle there is a rise in follicle stimulating hormone secretion in the first half of the cycle that stimulates follicular growth in the ovary.  If this inter-cycle rise of follicle stimulating hormone does not occur, final maturation of a single follicle and release of the egg (ovulation) does not take place. Progesterone produced by the corpus luteum can also feed back onto the hypothalamus and inhibit follicle stimulating hormone production.

In men, the production of follicle stimulating hormone is regulated by the circulating levels of testosterone and inhibin, both produced by the testes. Testosterone levels are sensed by nerve cells in the hypothalamus so that gonadotrophin-releasing hormone secretion is either increased or decreased.  The levels of inhibin are sensed by cells in the anterior pituitary gland.  If levels of testosterone and/or inhibin rise, follicle stimulating hormone production is reduced and vice versa if they fall, in a typical negative feedback loop.

What happens if I have too much follicle stimulating hormone?

Most often, raised levels of follicle stimulating hormone are a sign of malfunction in the ovary or testis. If the gonads fail to create enough oestrogen, testosterone and/or inhibin, the correct feedback control of follicle stimulating hormone production from the pituitary gland is lost and the levels of both follicle stimulating hormone and luteinising hormone will rise.  This condition is called hypergonadotrophic-hypogonadism, and is associated with primary ovarian failure or testicular failure.  This is seen in conditions such as Kallmann’s syndrome in men and Turner syndrome in women.   

In women, follicle stimulating hormone levels also start to rise naturally in women around the premenopause, reflecting a reduction in function of the ovaries and decline of steroid production.

There are very rare pituitary conditions that can raise the levels of follicle stimulating hormone in the bloodstream. This overwhelms the normal negative feedback loop and can cause ovarian hyperstimulation syndrome in women.  Symptoms of this include enlarging of the ovaries and a potentially dangerous accumulation of fluid in the abdomen (triggered by the rise in ovarian steroid output) which leads to pain in the pelvic area.

What happens if I have too little follicle stimulating hormone?

In women, a lack of follicle stimulating hormone leads to incomplete development at puberty and poor ovarian function (primary ovarian failure). In this situation ovarian follicles do not grow properly and do not release an egg, thus leading to infertility.  Since levels of follicle stimulating hormone in the bloodstream are low, this condition is called hypogonadotrophic-hypogonadism.

Sufficient follicle stimulating hormone action is also needed for proper sperm production.  In the case of complete absence of follicle stimulating hormone function in men, lack of puberty and infertility due to lack of sperm (azoospermia) can occur.  Partial follicle stimulating hormone deficiency in men can cause delayed puberty and limited sperm production (oligozoospermia), but fathering a child may still be possible. If the loss of follicle stimulating hormone occurs after puberty, there will be a similar loss of fertility.

 

Written: March 2011

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