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An overview of the gonads (testes, ovaries, and sex hormones)

From puberty to menopause, learn how these hormones affect libido, fertility and mood.

The testes and the ovaries produce the hormones most likely to change over our lifetimes. They are both reproductive organs and endocrine glands.

We discuss the reproductive hormones the testes and ovaries produce and their role in male and female characteristics, the menstrual cycle, and fertility.

What are the gonads?

The gonads are the glands in men (testes) and women (ovaries) that are responsible for producing gametes (sperm and eggs) for reproduction, as well as the hormones that are responsible for male and female characteristics.

They produce many of the same hormones but in different amounts.

Female hormones – hormones produced by the ovaries

The ovaries are responsible for producing eggs as well as manufacturing hormones. The primary hormones produced by the ovaries are oestrogens and progesterone.

1. Oestrogens

The ovaries produce three types of oestrogen – oestrone (E1), oestradiol (E2) and oestriol (E3). Oestradiol (E2) is the most potent; E1 and E3 are weaker forms of oestrogen.

Oestrogens play an important role in: 

  • The development of female secondary sex characteristics
  • The female reproductive system
  • Bodily functions, including bone formation, collagen production and mood regulation

Female secondary sex characteristics - In females, oestrogen levels increase at puberty, leading to the development of female secondary sex characteristics such as breasts, widening of the hips, and growth of pubic and underarm hair.

The female reproductive system - Oestrogen also plays a key role in the menstrual cycle – including the maturation and release of an egg at ovulation and preparing the uterine lining for fertilisation. 

  1. Oestrogen levels increase in the first half of the menstrual cycle and then decline, triggering menstruation if the egg has not been fertilised.
  2. Low levels of oestrogen during menstruation then triggers an increase in FSH to prepare a new egg for ovulation.
  3. If an egg is fertilised, oestrogen levels continue to rise throughout pregnancy, developing the placenta to nourish the growing baby and preparing the breasts to produce milk.
  4. Oestrogen levels peak in the third trimester and trigger the release of oxytocin by the hypothalamus which causes the womb to contract and labour to begin.

2. Progesterone

Progesterone is a steroid hormone that is made in the corpus luteum (the remains of the follicle after an egg has been released) in the second half of the menstrual cycle.

Progesterone prepares the endometrium for implantation and, if implantation is successful, its level rises rapidly to maintain the pregnancy.

The corpus luteum continues to make progesterone for the first eight to 12 weeks of pregnancy after which production switches to the placenta. As well as maintaining the health of the placenta to nourish the baby, progesterone causes changes in the body to accommodate the growing baby (e.g., the expansion of the womb and relaxation of ligaments) and prepare for childbirth (e.g., growth of milk ducts in the breasts). If the egg isn’t fertilised the corpus luteum breaks down and the production of progesterone drops, causing the menstrual cycle to start again.

The role of testosterone in women

Although it is known as the male sex hormone, women also produce small amounts of testosterone both in the adrenal glands and the ovaries.

Testosterone causes the bodily characteristics which are considered male, such as the deepening of the voice, growth of muscle, growth of facial hair and libido. In females, testosterone has a role in bone health, breast health, fertility, and sex drive.

What can affect female hormones?

1. Polycystic ovary syndrome (PCOS)

Polycystic ovary syndrome, also known as PCOS, is a common hormone condition that affects about one in ten women in the UK [1]. We have a full in-depth guide to PCOS – or you can read on for some more general information.

PCOS affects a woman’s ovaries, which are the reproductive organs responsible for protecting and releasing eggs in the womb into the fallopian tube for fertilisation. The ovaries are also responsible for producing oestrogen and progesterone, the hormones that regulate the menstrual cycle.

Normally, a woman’s ovaries produce an egg each month. With polycystic ovaries (an imbalance in the reproductive hormones that govern ovulation), this process can be disrupted.

During the monthly cycle, FSH stimulates the ovary to produce a follicle – a sac to contain an egg, and then LH triggers the ovary to release a mature egg.

In a woman with PCOS, the ovaries and ovulation process are affected. Its three main features are:

  1. Irregular periods
  2. High levels of male hormones (androgens)
  3. Cysts in the ovaries

In polycystic ovaries, several small, fluid-filled sacs grow inside of the ovaries. These small sacs contain some harmless follicles that are up to 8mm in size. Each one of the follicles contains an immature egg that never matures enough to activate ovulation.

The absence of ovulation decreases levels of oestrogen, progesterone, FSH and LH, while male hormone levels are higher than usual.

What causes PCOS?

The exact cause of PCOS remains a mystery, however, it often runs in families [2]. It is also believed that an increase of male hormones prevents the ovaries from producing hormones and releasing eggs normally.

Factors that are thought to play a role in PCOS include:

  • Inflammation – women with PCOS often have increased levels of inflammation in their bodies which has been linked to higher levels of androgens [3]. Being overweight can also impact a woman’s inflammation levels.
  • Insulin resistance – 70% of women with PCOS have insulin resistance which means their cells can’t use insulin properly [4]. This means that more and more insulin is produced to try to move glucose from the blood into the body’s cells. This elevated insulin is thought to be one of the factors that causes polycystic ovaries to develop.

Symptoms of PCOS

The symptoms of PCOS can vary from person to person. Many women experience very few symptoms, which can lead to some being unaware that they have PCOS. A study found that up to 70% of women with PCOS haven’t been diagnosed [5].

If symptoms are visible, women usually start to notice them around their first period, whilst others may only discover they have PCOS after they have gained a lot of weight or have had trouble trying to get pregnant.

PCOS has also been found to increase a woman’s risk of developing health problems in later life, such as type 2 diabetes and elevated cholesterol.

Common PCOS symptoms include:

  • Irregular periods or no periods at all
  • Excessive hair growth – usually on the face, chest or back
  • Weight gain
  • Difficulty getting pregnant due to irregular ovulation or failure to ovulate
  • Oily skin or acne
  • Hair loss or thinning on the head

Other ways PCOS can affect your body

Higher levels of androgens can impact your overall health in a variety of ways:

  • Infertility - As women with PCOS do not ovulate regularly or at all, the eggs that are required for fertilisation are not released making it difficult to become pregnant.
  • Sleep apnoea - A study found that women who are obese and have PCOS are 5 to 10 times more likely to develop sleep apnoea than those who don’t have PCOS [6]. The condition causes repeated pauses in breathing during the night, which can affect sleep.
  • Depression - Due to the hormonal changes and the difficulties PCOS presents such as unwanted hair and infertility, women can experience high levels of depression and anxiety [7].

How is PCOS diagnosed?

Many women report that getting a diagnosis for PCOS can be a struggle as there is no single test to identify whether you have it.  A diagnosis of PCOS can usually be made if other rare causes of the same symptoms have been ruled out and you meet at least two of the following criteria:

  • High androgen levels (such as testosterone)
  • Irregular periods or infrequent periods
  • Cysts in the ovaries visible on a scan

Usually, your doctor will send you to have an ultrasound scan and a blood test. The ultrasound scan uses sound waves to look for abnormal follicles and other problems with your ovaries and uterus. The blood test will check whether your male hormone levels are higher than normal.

How is PCOS treated?

There is no cure for PCOS, although symptoms can be managed by making lifestyle changes or taking medication [8].

  • Diet and lifestyle changes – treatment for PCOS often starts with lifestyle changes such as weight loss, diet, and exercise. Studies have found losing just five to ten percent of your body weight can help regulate your menstrual cycle and improve PCOS symptoms [9].
  • Medication – several medications can assist in regulating the menstrual cycle and treat PCOS symptoms such as hair growth and acne. Metformin can help to restore the menstrual cycle and Clomiphene, a fertility drug, can help women with PCOS get pregnant.
  • Surgery – if taking Clomiphene is not successful, a surgical procedure called laparoscopic ovarian drilling (LOD) can be performed. This involves using heat or a laser to destroy the tissue in the ovaries that are producing androgens.

2. Menopause

Menopause occurs when a woman’s reserve of viable eggs runs out and is characterised by a rapid decline in oestrogen. Women can experience fluctuations in oestrogen for years before they stop menstruating altogether, normally around the age of 50. Menopause is usually diagnosed one year after the last period.

What are the symptoms of menopause?

The symptoms of menopause can start up to ten years before a woman’s final period (perimenopause) and can continue for a decade after. They include:

  • Hot flushes
  • Vaginal dryness
  • Weight gain
  • Night sweats
  • Reduced libido
  • Difficulty concentrating
  • Low mood or anxiety
  • Breast tenderness
  • Reduced bone mass
  • Hair thinning or hair loss
  • Insomnia
  • More frequent urinary tract infections

How is menopause diagnosed?

For women of menopausal age, diagnosis is normally made by an assessment of symptoms. Menopause is not usually diagnosed with a blood test, as fluctuating hormone levels in the years preceding menopause can give a misleading diagnosis.

However, in women who are experiencing symptoms of menopause before their 45th birthday, a blood test to determine levels of FSH (which will be higher during menopause) and oestradiol (which will be lower) can indicate early menopause. You can check your levels with our Menopause Blood Test.

As the symptoms of menopause are very similar to those of other conditions, especially an underactive thyroid (which is often first diagnosed in women of menopausal age), a thyroid blood test can be helpful to distinguish between menopausal symptoms and a thyroid disorder.

You can check your thyroid function at home with our Thyroid Function Blood Test.

How are menopausal symptoms treated?

Many women go through menopause without need for any treatment, but for some women, the symptoms are very debilitating and can affect their quality of life. For these women, hormone replacement therapy (HRT) can do a lot to relieve symptoms.

Most HRT is a combination of oestrogen and progesterone and can be taken by oral tablets, skin patches, gels, or pessaries. There are risks associated with HRT; it can slightly increase the risk of breast cancer and blood clots in some women. Usually, these risks are outweighed by the benefits of treatment.

For more information on menopause, including other treatment options, visit our blog — all you need to know about the menopause.

Male hormones – hormones produced by the testes

The primary hormone produced by the testes is testosterone, although they also produce small amounts of oestradiol.

Testosterone levels increase significantly at puberty, which leads to the development of secondary sex characteristics in boys, such as:

  • Lowering of the voice
  • Development of muscle mass
  • Increase in body and facial hair
  • Enlargement of the penis

Testosterone is responsible for libido, sperm production, mood, and muscle mass all through adulthood. Testosterone levels typically peak when a man is in his 30s and then decline at less than 2% every year.

What can affect testosterone production?

It is very rare for men to overproduce testosterone; it is far more common to have low testosterone levels than naturally high testosterone.

Low testosterone (hypogonadism) has many causes, typically through damage to the testicles (through injury or chemotherapy), medication or anabolic steroid use, or as a side effect of other conditions such as diabetes, liver disease or obesity.

Low testosterone can also be caused by an inherited condition called Klinefelter Syndrome, where the male is born with an extra copy of the X chromosome. Late-onset hypogonadism is caused by falling levels of testosterone in older men.

What are the symptoms of low testosterone?

  • Low libido
  • Reduced muscle mass and inability to gain muscle in the gym
  • Erectile dysfunction
  • Infertility
  • Low mood and motivation
  • Small testicles
  • Difficulty sleeping
  • Low volume of semen
  • Low energy

How is low testosterone diagnosed?

Low testosterone is normally diagnosed by an assessment of symptoms and a blood test. As testosterone levels fall during the day, it is normally recommended that testosterone is tested in the morning before 10 am.

How is low testosterone treated?

Low testosterone can be treated by reversing any lifestyle factors that may be causing it, e.g.:

  • Sleeping better
  • Losing weight
  • Reducing alcohol intake

Find out more about how you can increase your testosterone levels naturally.

For men with confirmed hypogonadism (testosterone deficiency with symptoms), testosterone can be given orally, through injections or gels. This is known as testosterone replacement therapy (TRT).

What is the role of oestradiol in men?

A small amount of oestradiol is made in the testes, but testosterone can also be converted to oestradiol in the liver and fat tissues by the aromatase enzyme.

Oestradiol plays a role in sexual desire, the ability to achieve an erection as well as sperm production. While all men make oestradiol, in some men levels of oestradiol can be too high causing symptoms such as the growth of breast tissue (gynecomastia), infertility, and erectile dysfunction.

High oestradiol in men is often caused by having high levels of testosterone (usually by taking too much TRT or steroid misuse) which leads to more testosterone being converted to oestradiol. It can also be caused by obesity and through exposure to exogenous oestrogens e.g. plastics and Phyto-oestrogens in food.

How can high oestradiol be treated?

High oestradiol may be improved with lifestyle adjustments e.g., losing weight and reducing alcohol consumption, as well as keeping testosterone levels within normal levels.

If high oestrogen persists you may be prescribed aromatase inhibitors which reduce the amount of testosterone that is converted to oestradiol.

Where next?

Learn more about other glands and their role in hormone health:

  1. The hypothalamus – responsible for keeping the body in balance
  1. The pituitary gland – how hormones turn on and off
  1. The adrenals – glands that control your flight or fight
  1. The thyroid and parathyroid glands – hormones that affect metabolism
  1. The pancreas, pineal and thymus – endocrine glands for long-term health
  1. Hormone blood test buying guide

 


References

  1. NHS (2019). Polycystic ovary syndrome. [online] nhs.uk. Available at: https://www.nhs.uk/conditions/polycystic-ovary-syndrome-pcos/ [Accessed 23 Oct. 2019].
  2. Diamanti-Kandarakis, E., Kandarakis, H. and Legro, R. (2006). The Role of Genes and Environment in the Etiology of PCOS. Endocrine, 30(1), pp.19-26.
  3. González, F. (2012). Inflammation in Polycystic Ovary Syndrome: Underpinning of insulin resistance and ovarian dysfunction. Steroids, 77(4), pp.300-305.
  4. Marshall, J. and Dunaif, A. (2012). Should all women with PCOS be treated for insulin resistance?. Fertility and Sterility, 97(1), pp.18-22.
  5. March, W., Moore, V., Willson, K., Phillips, D., Norman, R. and Davies, M. (2009). The prevalence of polycystic ovary syndrome in a community sample assessed under contrasting diagnostic criteria. Human Reproduction, 25(2), pp.544-551.
  6. Ehrmann, D. (2012). Metabolic dysfunction in PCOS: Relationship to obstructive sleep apnea. Steroids, 77(4), pp.290-294.
  7. Cooney, L. and Dokras, A. (2017). Depression and Anxiety in Polycystic Ovary Syndrome: Etiology and Treatment. Current Psychiatry Reports, 19(11).
  8. The American College of Obstetricians and Gynaecologists (2017). Polycystic Ovary Syndrome (PCOS) - ACOG. [online] Acog.org. Available at: https://www.acog.org/Patients/FAQs/Polycystic-Ovary-Syndrome-PCOS [Accessed 23 Oct. 2019].
  9. Teede, H., Deeks, A. and Moran, L. (2010). Polycystic ovary syndrome: a complex condition with psychological, reproductive and metabolic manifestations that impacts on health across the lifespan. BMC Medicine, 8(1).