Hormones are chemical messengers that travel in the bloodstream and give instructions to organs, skin, muscles and other tissues. They help the body keep many systems in balance, from energy use to mood and sleep.
This short guide explains what are hormones and how they work, where they are made and what it means when levels are too high or too low. It is aimed at readers in the United Kingdom seeking clear, practical information.
Scientists have identified more than 50 of these chemicals so far, so the endocrine system is large and interconnected rather than limited to sex-related signals. Understanding this network helps make sense of symptoms that may seem unrelated, such as tiredness plus weight change.
The article will also preview the main glands that produce these messengers and explain when to speak to a GP and how tests for levels are usually done in the UK. This is a beginner-friendly overview to support better choices for long‑term health.
Key Takeaways
- Chemical messengers: they travel in blood to control many body processes.
- Over 50 different substances have been identified so far.
- They affect energy, mood, sleep and blood sugar, not just reproduction.
- Imbalances can cause mixed symptoms that seem unrelated.
- Later sections cover glands, testing and when to consult a GP in the UK.
What are hormones and why do they matter for health?
Tiny signalling molecules move through blood and set timing for many body functions. These chemical messages come from glands and circulate widely, though only certain tissues respond.
Hormones as chemical messengers carried in the blood
The endocrine system sends constant messages in the bloodstream. Glands release hormones chemical signals that travel in blood to reach organs and tissues.
How tiny changes in hormone levels can have big effects
A small shift in levels can change mood, appetite or energy. Think of it as “a little bit goes a long way”: minor variation in hormone levels often causes clear symptoms.
Hormones include more than reproduction-related chemicals
Hormones include many substances that control metabolism, stress response, temperature and fluid balance. These messages help decide when to sleep, when to eat and how to react to stress, so they shape everyday health.
- Glands release signals; target tissues respond.
- The system works continuously to keep the body stable.
- Small changes produce noticeable effects like tiredness or altered appetite.
How hormones work in the endocrine system
Imagine a key travelling through the body until it meets the correct lock on a single cell. This simple image explains why chemical messages travel in blood yet affect only certain tissues.
The “lock and key” model: receptors, cells, and target tissues
A hormone acts only where target cells have receptors matching that signal. Receptors sit on the cell surface or inside the cell. Only cells with the right receptor respond, so widespread circulation causes selective action.
Gland-to-gland signalling pathways
Endocrine glands often control each other. For example, the pituitary gland releases TSH that tells the thyroid gland to release thyroid hormones. Those thyroid outputs adjust metabolic rate, so a small change can alter energy use across the body.
Gland-to-organ signalling: pancreas, insulin and blood sugar control
The pancreas releases insulin after meals. Insulin helps muscles and liver take up glucose, keeping blood sugar steady. This gland-to-organ link shows how one gland’s signal affects whole-body balance.
| Pathway | Sender | Receiver | Effect |
|---|---|---|---|
| Gland-to-gland | Pituitary gland | Thyroid gland | TSH → thyroid hormones → changed metabolic rate |
| Gland-to-organ | Pancreas | Muscle & liver | Insulin → glucose uptake → stable blood sugar |
| Network effect | Multiple glands | Various tissues | Chains of signals can cause wide-ranging symptoms |
Because endocrine glands work in chains, a problem at one point can change output elsewhere. This communication system sets the scene for the gland-by-gland guide that follows.
For practical lifestyle guidance that supports healthy signalling, see these safe weight-loss tips.
Key endocrine glands and the hormones they produce
Key glands sit in predictable places around the body and each sends specific chemical signals that shape daily function. This short tour names each site, where it sits and its headline role in signalling.
Hypothalamus — the brain’s control hub
The hypothalamus sits at the base of the brain and links directly to the pituitary via the pituitary stalk.
It releases CRH, GnRH, GHRH, TRH, dopamine and somatostatin to adjust pituitary output.
It also makes oxytocin, stored and released by the pituitary.
Pituitary centre and its outputs
The pea-sized pituitary gland sits beneath the hypothalamus.
The anterior pituitary sends ACTH, FSH, GH, LH, TSH and prolactin.
The posterior releases ADH and oxytocin. These control other glands and growth.
Pineal and sleep
The pineal gland produces melatonin to help set the sleep-wake cycle.
Disruption of light cues can alter melatonin and cause sleep complaints.
Thyroid and metabolic rate
The thyroid sits low in the neck and releases T4 and T3.
These regulate metabolic rate, so shifts often show as changes in weight or energy.
Parathyroid and calcium balance
Small parathyroid glands behind the thyroid release PTH to control blood calcium and support bone health.
Adrenal response and pressure control
The adrenal glands sit above the kidneys.
They make cortisol and adrenaline for stress responses, plus aldosterone to help regulate salt, water and blood pressure.
Pancreas and blood sugar
The pancreatic islets produce insulin and glucagon to keep blood sugar stable, a key point in diabetes care.
Gonads: ovaries and testes
The ovaries produce oestrogen, progesterone and some testosterone; the testes make sperm and testosterone.
These signals affect fertility and the menstrual cycle.
For related cosmetic recovery stories, see Fraxel laser before and after.
What do hormones do in the body day to day?
Daily life runs on a hidden timetable of chemical signals that tell each organ when to act.
Metabolism, appetite and energy use
Signals control how the body turns food into fuel. After meals, insulin rises to steady blood sugar and to help cells take up glucose.
Leptin and ghrelin influence appetite, so energy intake and perceived hunger shift during the day.
Homeostasis: pressure, fluid, temperature and sugar
Keeping internal balance is constant. Aldosterone, ADH and other messengers help manage fluid and blood pressure.
Thermoregulation and sugar control use the same system to protect organs and support steady functioning.
Growth, development and life stages
Growth signals drive childhood and puberty. Levels change in pregnancy and with ageing, affecting many body systems.
Mood, stress response and sleep
Cortisol and adrenaline boost alertness during stress. Melatonin supports the sleep–wake cycle and affects perceived energy and hunger.
Sexual function and reproductive cycles
Oestrogen, progesterone and testosterone shape libido, fertility and cycle regularity. Receptors also exist in skin and hair, so shifts can show as acne or thinning hair.
- For signs of disrupted blood sugar, see diabetes warning signs.
Hormone imbalances: symptoms, causes and when to see a doctor
Many people miss early signs of imbalance because symptoms can feel unrelated and build slowly.
A hormone imbalance means the body has too much or too little of a signalling chemical. That can affect many organs at once, so symptoms vary widely.
Common symptoms
- Unexplained tiredness and weight change
- Low libido, irregular periods or fertility problems
- Sleep disruption, mood swings and digestive changes
- Skin changes, thinning hair or temperature sensitivity
Frequent conditions linked to imbalance
Key conditions include diabetes (insulin control), thyroid disease (low or high thyroid output) and polycystic ovary syndrome (PCOS), which causes irregular cycles and raised androgens.
Why imbalances happen
Causes range from tumours, autoimmune disease and inherited changes to life-stage or lifestyle drivers such as stress, pregnancy, ageing, puberty, sleep disruption and certain medicines.
Testing and who treats it
In the UK, a GP usually orders blood tests to check hormone levels. Some cases use saliva tests or specialist panels (for example SHBG/free androgen index). Imaging such as ultrasound or MRI follows if a gland problem is suspected.
| Step | Who | Common checks | Next action |
|---|---|---|---|
| Initial review | GP | History, blood tests | Manage or refer |
| Special tests | Primary care or clinic | Saliva, SHBG, free androgen index | Targeted treatment |
| Imaging | Hospital services | Ultrasound, MRI | Detect gland lesions |
| Specialist care | Endocrinologist | Advanced panels, biopsies | Long-term plan |
If symptoms persist, affect daily life, or suggest thyroid or blood sugar problems, see a doctor promptly. For more on neck-related signs, read about signs of thyroid problems.
Conclusion
A balanced endocrine network underpins many routine aspects of health.
Hormones are chemical messengers released by glands across the body. The endocrine system links the hypothalamus, pituitary, pineal, thyroid, parathyroids, adrenals, pancreas and gonads to regulate key functions.
Small shifts in levels can be tiny but mighty, changing energy, mood, sleep, weight and fertility. These signals do more than control reproduction; they shape everyday health.
In the UK, a GP can assess symptoms, order blood tests to check levels and refer to an endocrinologist when needed. Use this guide as a foundation for spotting patterns and asking informed questions, not for self-diagnosis.
