Follicle Stimulating Hormone
Follicle-stimulating hormone (FSH) is an important part of the reproductive system. It’s responsible for the growth of ovarian follicles. Follicles produce estrogen and progesterone in the ovaries and help maintain the menstrual cycles in women. In men, FSH is a part of the development of the gonads as well as sperm production.
What is Follicle stimulating hormone?
Follicle stimulating hormone (or FSH) is one of the gonadotrophic hormones; the other being luteinising hormone (or LH).
Both are released by the pituitary gland into the bloodstream.
Follicle stimulating hormone is one of the hormones essential to pubertal development and the function of women’s ovaries and men’s testes.
In women, this hormone stimulates the growth of ovarian follicles in the ovary before the release of an egg from one follicle at ovulation.
It also increases oestradiol production from the ovaries.
In men, follicle stimulating hormone acts on the Sertoli cells of the testes to stimulate 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 (HPG) axis.
Gonadotrophin-releasing hormone (GnRH) is released from the hypothalamus and binds to receptors in the anterior pituitary gland to stimulate both the synthesis and release of follicle stimulating hormone (FSH) and luteinising hormone (LH).
As per the definition of a hormone, the released follicle stimulating hormone is carried by the bloodstream and binds to receptors in the testes and ovaries.
In women, when FSH levels fall towards the end of the menstrual cycle.
This is sensed by the hypothalamus, which produces more gonadotrophin-releasing hormone (GnRH), which in turn stimulates the pituitary gland to produce more follicle stimulating hormone (FSH) and luteinising hormone (LH), and release these into the bloodstream.
The rise in follicle stimulating hormone stimulates the growth of the follicle in the ovary.
As the follicles in the ovary grow, they produce increasing amounts of oestradiol and inhibin.
In turn, these hormones act on the hypothalamus and pituitary gland to reduce the release of gonadotrophin-releasing hormone and follicle stimulating hormone (negative feedback).
This causes a fall in FSH, which prevents too many follicles developing each cycle.
The largest follicle is less dependent on FSH for its growth and is able to continue growing even if FSH levels fall.
However, smaller follicles can no longer survive as FSH levels fall due to negative feedback, enabling the emergence of a single dominant follicle.
High FSH Levels in Women
If you’re a woman with high FSH levels, this may indicate:
A loss of ovarian function, or ovarian failure
Polycystic ovarian syndrome, which is a condition in which a woman’s hormones are out of balance, causing ovarian cysts
A chromosomal abnormality, such as Turner’s syndrome that occurs when part or all of one of a woman’s X chromosomes is missing
High FSH Levels in Men
If you’re a man with high FSH values, this may indicate:
Klinefelter’s syndrome, which is a rare condition in men caused by an extra X chromosome that can affect male development
Testicles that are absent or not functioning properly
Testicles that have been damaged by a disease such as alcohol dependence
Testicles that have been damaged by treatments such as X-rays or chemotherapy
Low FSH Levels
Low FSH values may indicate that:
A woman isn’t producing eggs
A man isn’t producing sperm
The hypothalamus or pituitary gland, which are the hormone control centers in the brain, aren’t functioning properly
A tumor is interfering with the brain’s ability to control the production of FSH