Adrenaline, insulin, melatonin… they are words that you often come across on this site and they are all names of hormones. But what exactly is a hormone and what are all these different hormones for?

What are hormones?

Very simplistically defined, hormones are ‘signaling substances’ that are produced by our body to control or influence most functions and processes of our organism. They are produced by the endocrine glands (pituitary glands, pineal gland, hypothalamus, thyroid gland, adrenal glands, islets of Langerhans in the pancreas, thymus gland, ovaries, and testes) and enter our organs, tissues, and cells through the bloodstreams. So, they cover a long distance. If those cells and tissues have the right receptors, to which those hormones can attach, certain actions are initiated or slowed down.

Unlike the nervous system (for example, a contraction of a muscle is controlled by one or more nerves), the hormonal system has slow regulation.

Hormones affect both the long-term and short-lived processes in our body and the pituitary gland (a gland in our brain) plays the main role in this. Long-term processes include the growth and development of a child, puberty and the development of reproductive organs, pregnancy, and menopause. Daily short-term functions controlled and influenced by hormones include metabolism, digestion, thirst, blood pressure, urinary secretion, salt management, menstruation and sperm cell production, all kinds of organ functions, anxiety reactions, feelings, and emotions in general. After they have done their job, the hormones are finally broken down in our liver.

For the sake of completeness, it should be noted that, in addition to endocrine, there are also autocrine and paracrine hormones that work locally. They have an effect, respectively, on the gland through which they are excreted and on the neighboring cells of that gland.

What types of hormones are there?

Broadly speaking, hormones can be divided into two categories: protein hormones (e.g., adrenaline) and steroids (e.g., testosterone). Other sources divide them into three categories: amine hormones or adapted amino acids (e.g., adrenaline), peptide hormones or a chain of amino acids (e.g., insulin) and steroids or adapted cholesterol (e.g., testosterone). Depending on the function they perform, they can also be divided into different families such as the sex hormones, growth hormones, thyroid hormones, digestive hormones, and blood sugar hormones.

Each endocrine gland in our body creates its own hormone type and often those types influence each other. The hormone secretion and regulation are particularly complicated and is driven not only by the endocrine system (endocrine glands) but also by our nervous system.

The most common hormones in more detail

  • Adrenaline 

Adrenaline (epinephrine) and noradrenaline (norepinephrine), collectively called catecholamines, are produced in the cortex of the adrenal glands. These are the endocrine glands that are only two cm long and lie on top of the kidneys. The adrenal glands and the hormones they produce are ideally associated with stress situations such as anxiety, anger, and pain. The sympathetic nervous system stimulates the production of adrenaline and norepinephrine when we feel threatened or in (life) danger and thus prepares our body for action. Therefore, this hormone duo is also called the flight and fight hormones. Their production is a survival reflex of our body. But also, when our body seems to become unbalanced due to great physical exertion, hunger, cold or heat… the adrenaline level can peak.

Different receptors in our body respond to that instant influx of adrenaline. For example, there are alpha receptors in the blood vessels and digestive organs that cause vascular constriction and slower digestion, respectively.

In our heart, brain, and lungs, among others, there are beta receptors that will affect our heart rate and our breathing and that make us more alert. This explains why in stress states (increased adrenaline production) your heart beats faster, your breathing shifts up a gear, your pupils and the blood supply to your muscles increase, your blood pressure rises, you have goosebumps, and your body produces extra glucose as an energy source.

  • Aldosterone

Aldosterone is produced by the outer layer of the adrenal cortex and is important for the fluid and salt regulation in our body. It affects sodium and potassium management, and, in this way, it also plays a leading role in the control of blood pressure. If there is too much potassium or too little sodium in our blood, which reduces the volume of fluid and blood pressure, extra aldosterone is produced. This causes the kidneys to retain sodium and water and secrete potassium through the urine, causing blood pressure to rise again.

  • Cortisol 

Cortisol or the stress hormone is a vital hormone that suppresses the body’s response to all kinds of diseases, injuries, tissue damage and stress and is produced by the middle layer of the adrenal cortex. Just like adrenaline, it peaks with physical or mental stress (serious illness, trauma, extreme exertion, fever…), but it does take a little more time and therefore works in the longer term.

Cortisol allows us to release extra energy when a lot of ‘pressure’ is applied: it causes certain proteins to break down, releasing amino acids that in turn can be converted into glucose. So, it increases blood sugar, but it also increases appetite and inhibits fat burning. The cortisol level in the blood/urine/saliva is a good ‘stress indicator’.

At the same time, cortisol inhibits inflammatory reactions. That is why a person sometimes gets sick right after a stressful period.

In addition, cortisol also ensures that our body can function daily. It plays a role in the functioning of the immune system, food digestion, cholesterol control and sleep-wake rhythm. The production of cortisol is not evenly distributed throughout the day but follows our biological rhythm (circadian rhythm). When we wake up, for example, more cortisol is released, which induces our feeling of hunger.

By the way, research at the University of Nijmegen, which dates back to the end of 2016, shows that cortisol does not only prepare our body to endure stress situations. It also helps to calm our brain and body again and it compensates for the energy loss that comes with a stress state. Therefore, the name ‘stress-response hormone’ would be a happier choice.

  • Ghrelin and leptin

Ghrelin, like leptin, is involved in the feeling of hunger. It is especially secreted in the stomach and it arouses appetite. Therefore, it is also called hunger hormone. More is produced before meals, after which the amount decreases. Leptin is produced in our adipose tissue and stops the feeling of hunger.

A lack of sleep affects the production of these hormones and thus disturbs their balance. A study shows that the ghrelin concentration in the blood in short sleepers is about 15 percent higher and that leptin concentration drops by the same percentage. As a result, they are much hungrier when they wake up, are less likely to be saturated and have a higher BMI on average than the group that enjoyed a normal night’s sleep. If you do not get enough sleep (on average you need 7 to 8 hours of sleep per night), you have a good chance of gaining weight.

Ghrelin also encourages the pituitary gland to secrete growth hormone and it plays a role in the hippocampus, where it stimulates learning ability and adaptability. Furthermore, ghrelin also plays a role in the metabolism of carbohydrates. If you want to slim down, make sure your ghrelin level is not too high. You can influence this yourself by sleeping enough, building up enough muscles and eating a lot of healthy proteins.

The leptin quantity in our blood is regulated by the hypothalamus and aims to keep the energy supply (nutrition and consumption of energy) in our body as balanced as possible. People who are (severely) overweight (obesity) therefore have very high leptin concentrations and the result is that they become leptin resistant, in other words: they become insensitive to the action of leptin.

  • Insulin

Insulin allows our body cells to extract the glucose from the blood and thus store the necessary fuel. So, it lowers blood sugar or blood glucose levels. Without insulin, our cells cannot absorb glucose. Those who suffer from diabetes do not produce enough insulin or have cells that are not sufficiently sensitive to insulin intake.

  • Glucagon

Glucagon is a hormone that, like insulin, is produced by the pancreas and to a lesser extent also in the intestinal system. When our blood sugar levels are no longer at their level, it increases glucose concentration in the blood. It does this by releasing sugar stored in the liver. Sugar is processed in a different way in our liver, depending on its shape. Fructose is immediately converted into energy for our body, glucose can be temporarily stored and then given the name glycogen.

Diabetes patients often have a syringe with glucagon in case they get a hypo, too low blood sugar.

  • Estrogen

Estrogen, like testosterone, is a sex hormone (called androgens together) and is mainly made in the female genital organs (ovaries). Partly also in the inner layer of the adrenal cortex. There are different types of estrogen (estriol, estradiol and estron) that all have their own function. They play an important role in pregnancy, in the development of the female genital organs during puberty and in the regulation of the menstrual cycle. Together with progesterone, estrogen ensures that only one mature egg is present in the woman’s body during a natural cycle. They do this by suppressing the hormones that trigger the maturation of an egg and subsequent ovulation. If no fertilization follows, the concentration of estrogen and progesterone decreases again so that a new maturation process can occur.

Contraceptives contain progesterone and often estrogen precisely to prevent an egg from maturing. They are also important in the production of uterine mucus and in keeping the vagina supple.

During menopause, estrogen production (estradiol) stopped, which has a direct influence on the genital organs (e.g., dry vagina), temperature control, mood and emotions, and many organs and bodily processes. The development of bone decalcification or osteoporosis is also linked to it.

Estrogen is known as the ‘positive’ hormone: it makes you optimistic, it makes you energetic and ensures that you can better cope with stress. When estrogen concentration reaches a low point during premenstrual week (the fourth week of the menstrual cycle), many women suffer from PMS (premenstrual syndrome): bad mood, fatigue, depression, headache.

Men also have estrogen but to a very small extent.

  • Progesterone

Progesterone is a calming hormone. It has a reputation for making you loom and even that it can induce binge eating.

Progesterone is mentioned in the same breath as estrogen. It is produced in the ovaries and adrenal glands, where it also plays a role in the production of cortisol and adrenaline. Together with estrogen, it is responsible for regulating the menstrual cycle. In the second phase of that cycle, it is released by the corpus luteum.

Among other things, it prepares the uterine mucosa for implantation of a fertilized egg. During pregnancy, it is produced in large quantities by the placenta, and throughout pregnancy it plays an important role in the development of the baby.

  • Testosterone 

Testosterone is the ‘male hormone’ produced in the testes and adrenal glands. Women also produce testosterone, but to a much lesser extent. It is the hormone that stimulates libido. In embryos, it achieves the development of primary sex characteristics, and during puberty it causes the growth of penis, pubic hair (also in women) and testes, skeletal muscles, and the development of the voice depth. It is also necessary to make sperm.

Testosterone production also decreases in men during andropause (from about the age of 50).

  • Oxytocin 

Oxytocin or the cuddle hormone is produced by the hypothalamus but stored in the pituitary gland. It gets its name from the fact that it gets out when you cuddle. It creates a sense of attachment and feeling good together. It also plays an important role in reproduction: it regulates the ejaculation in the male and muscle contractions of the vagina and uterus in the female, it achieves the contractions of the uterus during childbirth and the shooting reflex of the milk during breastfeeding.

  • Thyroid hormones 

Thyroid hormones (T3 and T4) regulate energy metabolism (combustion) so that energy is released to make our body function or grow.

  • Melatonin 

Melatonin or the sleep hormone is secreted by the pineal gland in the brain and regulates our sleep-wake rhythm (or circadian rhythm). The amount of melatonin in the body is controlled by the daylight that the eyes perceive: as soon as your eyes see daylight, they give a signal to slow down melatonin production. When there is no more daylight, the inhibition stops, and you become sleepy.

Furthermore, our biorhythm also plays a role in this: just before we wake up, nerve cells in our hypothalamus release proteins (orexins), which activate our body, and our adrenal glands create a high dose of cortisol (stress hormone) that makes us alert and awake as an alarm clock.

Joseph Mandell

Mandell is currently working towards a medical degree from the University of Central Florida. His main passions include kayaking, playing soccer and tasting good food. He covers mostly science, health and environmental stories for the Scientific Origin.