The pituitary gland – the mighty pea
The pituitary gland is a pea-sized organ at the base of the brain. For such a tiny organ, the pituitary has a huge effect on the body. And it’s the hormonal headquarters for human reproduction! Like all hormone-producing glands, the pituitary sends messages through the hormones it makes and releases into the blood.
The tiny hormones act as chemical messengers, reaching every part of the body. Different cells react in different ways to these messages, so a single hormone signal can have many different effects. But the pituitary is unusual; it has a special trick. Many of its hormones control other hormone-producing glands. For this reason, the pituitary is sometimes called ‘The Master Gland’. A signal from the pituitary can change which hormones are being released elsewhere in the body, and so it has great power over body processes.
But there is a higher power still: the brain is directly connected to the pituitary and can tell it what to do. This is done through a part of the brain called the hypothalamus, which sits directly above the pituitary. The hypothalamus sends signals to the pituitary using hormones, which means the hypothalamus itself is a gland. (Yes you have glands in your brain – they are everywhere!)
By its control of ‘The Master Gland’, the brain controls the timings and coordination of many different hormonal signals in the body. In this way, the pituitary serves as the main connection point between the brain and the endocrine system (the system of glands and hormones).
The pituitary gland responds not only to the hypothalamus’ hormones, but also to hormones that arrive from other parts of the body. These help feed back information about what is happening in other organs. The pituitary gland makes and releases a large number of different hormones for different purposes. These include hormones that control reproduction and growth . You can find out more about this important organ in our article the Pituitary Gland.
Puberty
During puberty, male and female bodies change, developing in ways that allow for future sexual reproduction. This process is driven by hormones, which control how bodies change during this time and how they function afterwards.
Puberty is kicked off by the hypothalamus, which releases a hormone that tells the pituitary to get things started. The pituitary then releases hormones that signal to the ovaries and testes that it’s time to start making the reproductive hormones needed for puberty.
The main reproductive hormones that drive puberty are oestrogen and progesterone from the ovaries, and testosterone from the testes. These hormones (and others released alongside them) affect different cells, tissues and organs in different ways. This drives the many changes experienced at puberty. Key hormones for puberty:
The menstrual cycle
From puberty, the female body goes through a cycle of hormonal changes which drive the production and release of eggs, and preparation for a possible pregnancy.
This cycle ends in menstruation: the bleeding that is more commonly known as a period. This cycle involves many different hormones, released from the pituitary gland in the brain and ovaries. Levels of different hormones rise and fall through the cycle, and affect each others’ release. Oral contraceptive pills work by changing hormone levels to prevent the release of eggs.
Most women have a menstrual cycle from puberty until later life. It then stops as the levels of the hormone oestrogen decrease. This is called menopause, but the cycle doesn’t just pause - it stops for good. For more detail, check out our article about the menstrual cycle and about menopause. Key hormones for the menstrual cycle:
- Follicle Stimulating Hormone (FSH)
- Oestrogen
- Luteinising Hormone (LH)
- Progesterone
Pregnancy and labour
During pregnancy, hormones are important in controlling how the mother’s body changes and responds to the foetus. Hormones are produced by the mother, foetus, and placenta.
Changing levels of hormones control the timings of events including egg release, the timing of when labour begins, pushing during labour, and lactation (for breastfeeding). Find out more, including why pregnancy tests used to involve live frogs, in our article about hormones in pregnancy and labour.
Key hormones for pregnancy and labour:
- Human Chorionic Gonadotrophin (hCG)
- Progesterone
- Oestrogen
- Oxytocin
- Prolactin
Male reproductive system
In male bodies, testosterone is the main reproductive hormone. It is made in the testes (testicles). Testosterone controls the production of sperm, and the development of the adult male body.
The testes release testosterone in response to hormonal signals from the pituitary gland. If testosterone levels get too high, the brain signals to the pituitary that it should stop sending these signals. This then stops the testes from releasing more testosterone. This is an example of a negative feedback loop.
Key hormones for the male reproductive system:
A note about ‘male’ and ‘female’ hormones
Although we most often hear about testosterone in males, and oestrogen in females, it is a bit misleading to call these ‘male’ and ‘female’ hormones.
Like most hormones, testosterone and oestrogen have a wide variety of effects on the body. At high levels they help develop and control male and female organs and processes. But at lower levels they play other roles.
This means they are not really ‘male’ and ‘female’ hormones. At low levels, testosterone is also found in women, and oestrogen is also found in men.
Reproductive hormones and medicine
Reproductive hormones have powerful effects on the body. There are many medical conditions caused by hormone imbalances. Endocrinologists are expert in understanding how hormones work in the body and how to help people with different conditions.
Reproductive hormones are used in a variety of different therapies. They can be taken as pills, absorbed through the skin, or injected.
The most common way that reproductive hormones are taken is as the contraceptive pill. These pills contain progesterone and/or oestrogen. These hormones give a signal that causes the pituitary gland to stop the development and release of eggs in the ovaries.
A different mix of hormones can be used to encourage pregnancy in cases of infertility, or during in vitro fertilisation (IVF) treatment.
Reproductive hormones can also be given to boost naturally low levels of the hormones in the body. The most common reason for this is to help with symptoms of menopause. They are also used to treat people with gender dysphoria who wish to change their body’s appearance to match their gender identity.
Treatments are also available to block the effect of reproductive hormones when levels are too high, or where this would otherwise be helpful. For example, hormone blockers are given when treating some types of cancers that are stimulated by hormones.
