What are hormones, and what do they do?

Most of our hormones are made by endocrine glands, which then release them into the bloodstream. They then travel through the body to the parts where they’re needed. The main endocrine glands include the

• pancreas,
• gonads (testicles and ovaries),
• thyroid gland,
• parathyroid glands,
• adrenal glands, and the
• pituitary gland.

Substances known as local hormones (or tissue hormones) are produced in individual cells, not in glands. They work exactly where they’re needed by having an effect on neighboring cells.

Some organs also produce hormones in addition to doing their main job. One example is the kidneys, which cleanse our blood and also make the hormone erythropoietin (EPO). EPO stimulates the production of blood cells in our bone marrow. The nervous system can also affect our hormone levels.

Our hormone levels are finely balanced to make sure they can regulate the processes in our body according to what is needed. A good example is the hormone insulin. It is produced in the pancreas and regulates our blood sugar levels.

Insulin ensures that the sugar in our blood gets into our cells. They use it for energy. But our blood sugar levels vary depending on what we eat and when we eat it. The pancreas reacts to these changes exactly as needed: It releases more insulin if there’s too much sugar in the bloodstream, and less insulin if there’s not enough blood sugar.

Often, a hormone regulates more than just one body function. One example is when there’s a lot of sugar in someone’s blood: The insulin that is released to bring the sugar levels back down also stops the body from burning fat. As a result, the cells use the sugar for energy first.

Sometimes two different hormones have opposite effects, like insulin and glucagon. Glucagon is also made in the pancreas, but it’s only released if there’s not enough sugar in the blood. This happens when someone fasts (doesn't eat anything for some time), for example. Glucagon makes our muscles and liver release stored sugar into our bloodstream so that our body's cells are always supplied with energy.

Often, hormones that are higher up in the “hormone hierarchy” regulate how much of another hormone is released. Many of these higher-ranking hormones are produced in the pituitary gland or the hypothalamus in the brain. This type of regulation is often based on a negative feedback loop. For instance, the pituitary gland reacts to the thyroid hormone levels in our blood: If they’re too low, the pituitary gland releases TSH (thyroid-stimulating hormone, also called thyrotropin), and that makes the thyroid produce more hormones. When the thyroid hormone levels in the blood increase, the pituitary gland releases less TSH.

Our hormonal system (endocrine system) is complicated: Each hormone has its own specific functions, but often regulates a process in the body together with other hormones. And each hormone can affect several other processes at the same time.

The insulin produced by the pancreas ensures that cells can absorb sugar for energy. But other hormones, particularly the thyroid hormones T3 and T4, are also involved. They trigger metabolic processes (chemical reactions in our body), which use up energy and sugar. These processes may raise your body temperature and increase your heart rate, for example.

Our “stress hormones” increase the amount of energy our bodies use up too. One well-known example is adrenaline (also called epinephrine). When we’re frightened or doing something strenuous, the adrenal glands release adrenaline into our blood. This hormone increases our pulse and blood pressure. It also causes sugar and fat to be released so that it can be used for energy. Glucocorticoids, hormones that are produced in the adrenal cortex, have similar effects. Cortisol is a well-known glucocorticoid hormone. It is used as a steroid medication to treat various health complaints. The human growth hormone somatotropin, which is made in the pituitary gland, affects our energy levels too.

The kidneys remove water and salts from our bodies by releasing them into our urine. Hormones such as aldosterone help regulate the water and salt removal process to keep blood pressure stable. Aldosterone is made in the adrenal cortex. But the hormones renin and angiotensin also play a role. Another hormone that’s involved comes from the hypothalamus in the brain. Known as anti-diuretic hormone (ADH) or vasopressin, it can reduce the amount of urine a person passes when necessary.

Our bodies need calcium and phosphate for a process known as “bone metabolism.” These minerals also have other functions in the body. In the bones they are like bricks that are inserted when bone tissue grows, or removed from existing bones if they’re needed elsewhere. Hormones ensure a healthy balance here: The parathyroid glands produce a hormone called “parathyroid hormone." One of its jobs is to promote the breakdown of bone tissue and increase blood calcium levels. Calcitonin, a hormone made in the thyroid gland, can bring calcium levels back down. Other hormones involved in bone metabolism include the growth and sex hormones. Vitamin D plays a role too. For example, it controls how much calcium our bowel absorbs from what we eat.

Growth hormones like somatotropin stimulate cell division and cell growth, as well as having an effect on our bodies’ energy and water levels. By doing this, they help the body grow. When puberty starts, the sex hormones begin to affect our bodies too. The sex hormone testosterone, which is made in the testicles, promotes muscle growth and body hair growth, for example. The sex hormones produced in the ovaries – the estrogens – make the mammary glands in the breasts grow, among other things.

The sex hormones make our reproductive organs develop and start working. Hormones also control the menstrual cycle and the physical changes occurring in the body during pregnancy and after giving birth. Another important task these hormones have is making us feel sexual desire.

It is worth noting that sex hormones aren’t only produced in the testicles and ovaries. Smaller amounts are also made in the adrenal glands, the liver, fatty tissue and our skin, which is why men also produce estrogen and women produce testosterone – but in different amounts.

Various health problems are due to the body having

• too much,
• too little
• or a complete lack

of a particular hormone.

A typical example of the “too much” problem is an overactive thyroid gland (hyperthyroidism), which results in too many thyroid hormones. This causes the metabolism to go into overdrive, which can lead to a rapid heartbeat, diarrhea and/or weight loss.

An underactive thyroid (hypothyroidism), on the other hand, means the thyroid doesn’t produce enough of these hormones. This can result in tiredness and a drop in physical fitness.

One example of a disease where there's a lack of a hormone is type 1 diabetes. Here the pancreas either produces just a very small amount of insulin or none at all.

Sometimes, the problem is related to how well a hormone works rather than how much of it there is. This happens at the beginning of type 2 diabetes, for instance: The pancreas does produce insulin but the cells stop reacting to it and don’t take in enough sugar from the blood. This results in a rise in blood sugar levels.

Hormones are also used as medication, like insulin in the treatment of diabetes. If your body makes too many hormones, you can take medication to reduce the levels. For example, anti-thyroid drugs reduce the amount of thyroid hormones produced. Birth control pills work by changing hormone levels to stop the ovaries from releasing an egg.