Hormones: What They Are, Types and How They Work

Every second, dozens of invisible messages circulate through your body, determining when you feel hungry, how your metabolism works, how you respond to stress and whether you sleep deeply or wake up exhausted. These messages are delivered by hormones – chemical substances that influence almost every process in the body.

Hormones work like an invisible coordination system, sending signals to organs, muscles, skin and other tissues so that the body can function properly. If their levels rise or fall beyond normal limits, the body's internal balance can be thrown off. To understand how hormones affect your health, however, you first need to know what hormones actually are, how they work and through which mechanisms they exert their effects.

What are hormones and how do they work in the body

Hormones are chemical substances produced by the endocrine glands. They act as the body's internal communication system, controlling vital processes at every stage of life. They are released into the blood by specialised groups of cells – the glands – and then circulate through the body, delivering instructions to target cells.

Hormones are the chemical messengers of the endocrine system

Hormones are chemical messengers produced in the endocrine glands. These glands are specialised groups of cells that make up the endocrine system and release their substances directly into the bloodstream.

Once in the blood, hormones travel to their target organs or tissues, where they bind to specific receptors and deliver precise information. Each hormone has a clearly defined job and controls a particular organ or type of cell. Insulin, for example, regulates blood sugar levels. Oestrogen and progesterone govern the menstrual cycle, pregnancy and other important processes in the female body.

Together, all these hormones coordinate the body's internal functions and maintain homeostasis, that is, the body's internal balance. In other words, they play an important role in stabilising blood sugar, blood pressure, body temperature and many other vital parameters.

Hormones and the difference between the endocrine system and the nervous system

The endocrine system and the nervous system work together to control bodily functions – though they do so through different mechanisms.

The nervous system transmits information via electrical impulses and responds almost instantly to stimuli, whereas the endocrine system releases hormones into the blood, which act more slowly and regulate long-term processes such as growth, development, metabolism and the menstrual cycle.

The type of "messenger" also differs between the two systems. The endocrine system communicates via hormones, which are transported in the blood to organs and tissues, while the nervous system uses neurotransmitters to relay rapid signals between neurons.

How do hormones act and how do they affect target cells?

Hormones are released into the blood and transported to their target organs or tissues, where they interact with specific cell receptors. Their effect on the body depends on the type of hormone and on the mechanism by which it influences cell activity.

Hormones are released and transported via the blood

The endocrine glands release hormones directly into the bloodstream. Once in the blood, they circulate throughout the entire body, yet they only affect their target organs and act exclusively on cells that have matching receptors.

Depending on the type of hormone, the way it is transported in the blood also differs. Steroid hormones such as cortisol, oestrogen and progesterone, for instance, are cholesterol derivatives and are hydrophobic – meaning they cannot circulate freely in the watery plasma. For this reason, they are transported bound to plasma proteins in order to reach their target cells safely.

Hormones act via specific cell receptors

To exert their effects on target organs, hormones must bind to specific cell receptors. These receptors are located either in the cell membrane or in the cell nucleus. Once binding has occurred, hormones deliver the message to the cell that triggers a particular response.

Hormones that cannot cross the cell membrane bind to membrane receptors and trigger biochemical reactions inside the cell that alter its activity. Hormones that can enter the cell – such as steroid hormones – bind to nuclear receptors and can activate or suppress specific genes in the DNA.

Hormones work on the lock and key principle

The way hormones work is based on a principle known as the lock and key principle. Just as a key fits only one particular lock, each hormone has a specific chemical structure that is compatible only with certain receptors.

That is why each hormone can bind only to cells with matching receptors. This explains why different hormones affect only certain tissues and organs, even though they circulate throughout the entire body.

Once binding takes place, hormones trigger a precise cellular response. This may be the stimulation of a function, the inhibition of a process, a change in the rate of cell division, or an adjustment in the production of other substances the body needs.

Hormones are regulated by negative and positive feedback

The amount of each hormone the glands produce is controlled very precisely. The human body is able to judge when a smaller or larger quantity of a particular hormone is required and controls its release through self-regulating mechanisms. The most important of these are negative and positive feedback.

Negative feedback is more common and its role is to keep hormone levels within optimal ranges. If the level of a hormone rises above a certain threshold, the body reduces its release in order to prevent an excess.

Positive feedback is rarer and involves a temporary increase in hormone release until a particular physiological goal is achieved – after which the mechanism stops.

Hormonal disorders arise when these control mechanisms are impaired and can no longer prevent the insufficient or excessive release of certain hormones. Such situations can disrupt hormonal balance and impair the normal functioning of the body.

Hormones and the endocrine system – the hormone-producing glands

Most hormones in the body are produced in specialised organs that make up the endocrine system. This system consists of a collection of glands that produce hormones and release them directly into the blood.

Each gland has a clearly defined role and secretes specific hormones that regulate essential functions such as growth, metabolism, blood sugar levels and the stress response:

• The hypothalamus: produces corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone, dopamine, oxytocin and somatostatin, which control the activity of the pituitary gland and maintain the body's internal balance.
• The pituitary gland: also known as the master gland, it secretes hormones involved in development, lactation and reproductive function – such as adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), human growth hormone (hGH), luteinising hormone (LH), prolactin, thyroid-stimulating hormone (TSH), antidiuretic hormone (ADH) and oxytocin.
• The thyroid gland: produces thyroxine (T4), triiodothyronine (T3), reverse T3 and calcitonin, which control metabolism, body temperature and energy levels.
• The adrenal glands: release hormones involved in the stress response, as well as hormones that help regulate blood pressure and electrolyte balance (adrenaline, noradrenaline, cortisol, aldosterone, DHEA and androgens).
• The endocrine portion of the pancreas: the endocrine cells of the pancreas produce insulin and glucagon, which keep blood sugar levels within the normal range.
• The ovaries and testes: release the sex hormones (oestrogen, progesterone and testosterone).
• 

Not all organs and tissues that release hormones belong to the endocrine system. Although adipose tissue, the kidneys, the liver and the placenta all secrete hormones, for example, they are not counted as part of the endocrine system.

How do hormones affect menstruation and the cycle?

The menstrual cycle is the result of hormone levels governed by the interplay between the brain and the ovaries. Monthly fluctuations in hormone levels determine ovulation, the building up of the womb lining and the onset of menstruation – and any change in this balance can affect the regularity and characteristics of the cycle.

Hormones govern the monthly menstrual cycle

The menstrual cycle is primarily regulated by the female hormones oestrogen and progesterone. They cause the womb lining to thicken and prepare the body month after month for a possible pregnancy.

The pituitary gland secretes FSH (follicle-stimulating hormone) and LH (luteinising hormone), which coordinate the maturation of the follicle and trigger ovulation. If pregnancy does not occur, the womb lining is shed during menstruation and the cycle begins anew.

The balance between these hormones is the foundation of a regular menstrual cycle with predictable intervals between periods. On your period days, use hypoallergenic menstrual products made from 100% organic cotton so that you feel as comfortable as possible.

Hormones and cycle disorders

Hormonal imbalances can lead to cycle disorders. Irregular periods, absent ovulation and abnormal bleeding may point to an imbalance at the level of the ovaries, the pituitary gland or the thyroid, and are associated with conditions such as polycystic ovary syndrome (PCOS) or thyroid problems.

In women, these imbalances may manifest as severe period pain, menorrhagia (heavy bleeding) or very long or very short cycles – symptoms that should be assessed by a doctor.

What types of hormones are there and how do they work?

There are many types of hormones, which can be classified not only by the gland that produces them but also by their chemical structure and the way they act on target cells. Depending on their composition, they are either water-soluble or fat-soluble – an aspect that in turn determines how quickly they act, how long their effects last and the mechanism by which they influence bodily functions.

Peptide hormones and their metabolic function

Peptide hormones are made up of chains of amino acids and are water-soluble, meaning they dissolve easily in the blood. They therefore circulate freely in the plasma and require no transport proteins. They cannot cross the cell membrane and so bind to receptors on the cell surface, where they trigger rapid reactions inside the cell – which means their effects set in quickly.

The role of peptide hormones is to regulate metabolism and growth. Growth hormone, for instance, is involved in the development of tissues and body mass. Insulin, another peptide hormone, regulates blood sugar levels.

Steroid hormones – cholesterol derivatives

Steroid hormones are derived from cholesterol and are fat-soluble, meaning they dissolve in fats. This allows them to cross the cell membrane with ease. Unlike peptide hormones, however, they must be bound to transport proteins in order to circulate in the blood.

Once inside the cell, steroid hormones bind to intracellular receptors and can directly influence gene expression, thereby producing longer-lasting effects on the body. This group includes cortisol, which is involved in the stress response, as well as testosterone, oestrogen and progesterone.

Amino acid-derived hormones

Amino acid-derived hormones are generally formed through the modification of amino acids such as tyrosine or tryptophan. This category includes adrenaline, thyroxine and melatonin.

Depending on the type, amino acid-derived hormones may have rapid effects similar to peptide hormones, or longer-lasting effects on complex metabolic processes and physiological functions.

What functions do hormones have in the body?

Hormones coordinate numerous processes and functions that enable the body to adapt to its internal and external environment and to function optimally:

• They regulate metabolism
• They influence growth and development
• They control reproductive function
• They govern the stress response
• They regulate sleep and the circadian rhythm
• They influence appetite and body weight

For this reason, even a small change in hormone levels can bring about major changes in the body and give rise to various conditions that require medical treatment.

What are hormonal disorders and how do hormonal imbalances arise?

Hormonal disorders occur when the level of one or more hormones rises above or falls below normal limits – or when target cells fail to respond appropriately to the hormonal signal. These imbalances can affect the functioning of several bodily systems and manifest differently depending on the hormones involved.

Hormonal disorders – common causes

Each type of hormonal imbalance and the conditions associated with it can have different causes. Among the main situations that lead to disturbances in hormone levels are:

• Endocrine conditions or damage to an endocrine gland
• Autoimmune conditions that affect the endocrine glands
• Chronic stress, which causes raised cortisol levels
• An unbalanced diet, which can affect hormonal balance
• Inherited genetic conditions that can impair the structure or function of an endocrine gland

Hormonal disorders – common symptoms

The symptoms of hormonal disorders differ depending on the hormones involved, but chronic fatigue is one of the most common signs. Hormonal imbalances can also cause weight fluctuations – either through changes in appetite or through a change in the way the body uses energy.

In women, the symptoms of a hormonal imbalance may include cycle disorders, more intense period pain or changes in the heaviness of bleeding. In men, a hormonal imbalance such as low testosterone can lead to reduced libido, mood swings and a decline in muscle mass.

Hormonal disorders and endocrine conditions

Hormonal disorders are often linked to various endocrine conditions.

Diabetes, for example, arises as a result of a disturbance in insulin, the hormone responsible for regulating blood sugar. Hypothyroidism and hyperthyroidism are conditions of the thyroid gland that affect metabolism and energy levels.

Prolonged exposure of the body to excessive cortisol levels can cause Cushing's syndrome – a serious endocrine condition that can lead to weight gain, high blood pressure and skin changes.

In women, polycystic ovary syndrome (PCOS) affects the female hormones and can influence ovulation, fertility and the regularity of the menstrual cycle.

How are hormones tested and when are hormone tests recommended?

There are several testing methods that can measure hormone levels. They are recommended according to symptoms and clinical suspicion, and are intended to help identify imbalances and establish an accurate diagnosis.

Blood tests for hormones

Hormonal blood tests measure the concentration of particular hormones in the serum or plasma and provide information about the functioning of the endocrine glands. The most common of these include TSH to assess thyroid function, as well as cortisol, oestrogen and testosterone. Their purpose is to assist in diagnosing hormonal imbalances and in monitoring specific treatments.

Hormone tests in saliva and urine

Saliva testing is often used to assess cortisol levels, particularly to track fluctuations over the course of the day and to understand the natural rhythm of its release.

Urine tests can analyse hormone metabolites, that is, the substances produced when hormones are processed by the body. These tests are sometimes used for a more detailed assessment of endocrine function.

When are hormone tests recommended?

Your doctor may recommend a series of hormone tests if you notice persistent symptoms of hormonal disorders such as chronic fatigue or cycle disorders. Hormone tests are also indicated for both women and men in order to assess reproductive function in cases of fertility problems.

Other common situations in which hormone tests are recommended to confirm a diagnosis include suspected hypothyroidism, hyperthyroidism and diabetes.

How do you maintain your hormonal balance and regulate hormones naturally?

A balanced hormonal system requires habits that support the optimal functioning of the endocrine system day after day. The most important steps you can take are:

• Eat a balanced, nutrient-rich diet.
• Exercise regularly.
• Make time for rest and for stress-management techniques.

Frequently asked questions about hormones

Hormones influence almost every process in the body – which can make it all the harder to understand the role they play, how they work and why their levels can have such a strong effect on your mood and your health. To help you make sense of it all, here are answers to the most frequently asked questions about how the endocrine system works.

What are hormones, briefly explained?

Hormones are chemical messengers produced by the endocrine glands and released into the blood in order to convey information between different organs and tissues. They regulate essential bodily functions such as metabolism, growth, reproduction, sleep and the stress response.

Which is the most important hormone?

There is no single hormone that counts as "the most important". Each hormone has a specific role and contributes to maintaining the body's internal balance. Hormones act interdependently within the endocrine system – the body's optimal functioning depends on the balance between them, not on any single hormone.

How can you tell whether you have a hormonal disorder?

The symptoms of hormonal disorders may include persistent fatigue, weight fluctuations, cycle disorders and unexplained mood swings. To confirm a hormonal imbalance, your doctor may recommend a series of hormone tests depending on the symptoms present.

Can hormones be regulated naturally?

The body naturally has a self-regulating system that keeps hormone levels within optimal ranges. This system can be supported through lifestyle – with a nutrient-rich diet and regular exercise, which help maintain the body's natural hormonal balance. If imbalances do arise, however, medical treatment is usually required.

What is the connection between hormones and menstruation?

The female hormones oestrogen and progesterone govern the menstrual cycle and the way the body prepares each month for a possible pregnancy. A hormonal imbalance can therefore lead to irregular bleeding, absent ovulation or changes in the heaviness of bleeding.

Which hormone tests are the most common?

The most common hormone tests include:

• Thyroid hormone tests to assess thyroid function.
• Hormone tests for cortisol – in cases of persistent stress or suspected adrenal conditions.
• Oestrogen and testosterone tests to assess reproductive function.

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