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[Endocrine](/glossary?system=Endocrine)

# Hormone

hor·mone - HOR-mohn

## Definition

A hormone is a [chemical messenger](/glossary/neurotransmitter) produced by glands in the endocrine system that travels through the bloodstream to target organs and tissues, where it regulates specific physiological processes. Hormones control an enormous range of body functions including growth, metabolism, reproduction, mood, sleep, appetite, immune function, and [stress response](/glossary/stress-response). Even tiny amounts of hormones can produce profound effects on body function.

The major hormone-producing glands include the hypothalamus and pituitary (the master regulators in the brain), [thyroid](/glossary/thyroid), parathyroids, adrenals, pancreas, ovaries, and testes. These glands form an interconnected network where hormones from one gland influence the activity of others through complex feedback loops. The hypothalamic-pituitary axis coordinates much of this communication, acting as the body's central hormonal control system.

Hormones can be classified by their chemical structure into three main categories: steroid hormones (derived from cholesterol, including [cortisol](/glossary/cortisol), estrogen, testosterone, and progesterone), peptide/protein hormones (including insulin, growth hormone, and thyroid-stimulating hormone), and amino acid derivatives (including thyroid hormones, epinephrine, and [melatonin](/glossary/melatonin)). Each type [has](/glossary/hyaluronic-acid) different mechanisms of action, rates of clearance, and methods of transport in the blood.

## Also Known As

Chemical messenger Endocrine signaling molecule 

## Key Facts

-   • The endocrine system produces over 50 different hormones that regulate virtually every body function. 
-   • Hormone levels fluctuate throughout the day, across the menstrual cycle, and over the lifespan. 
-   • Endocrine disruptors - chemicals found in plastics, pesticides, and personal care products - can interfere with hormone function. 
-   • Blood tests for hormone levels must account for timing, as many hormones have circadian patterns. 
-   • Hormonal imbalances can affect every system in the body, producing symptoms that are often vague and easily misattributed. 

## How It Relates To Your Health

Hormonal health is foundational to overall well-being. Conditions like hypothyroidism, diabetes, [PCOS](/glossary/pcos), adrenal insufficiency, and [growth hormone](/glossary/growth-hormone) deficiency all result from hormonal imbalances. If you're experiencing symptoms like unexplained fatigue, weight changes, mood shifts, menstrual irregularities, or changes in libido, hormonal testing may be appropriate.

Hormone testing typically involves blood draws timed to specific points in the day or menstrual cycle. Treatment options range from hormone replacement therapy to medications that modulate hormone production or activity, to lifestyle changes that support healthy hormone balance.

## Related Terms

[Cortisol](/glossary/cortisol)[Insulin](/glossary/insulin)[Estrogen](/glossary/estrogen)[Testosterone](/glossary/testosterone)[Progesterone](/glossary/progesterone)[Melatonin](/glossary/melatonin)[Thyroid-Stimulating Hormone](/glossary/thyroid-stimulating-hormone)[Growth Hormone](/glossary/growth-hormone)[DHEA](/glossary/dhea)

## Sources

1.  [Hormones](https://my.clevelandclinic.org/health/articles/22464-hormones) - Cleveland Clinic
2.  [Endocrine System](https://www.ncbi.nlm.nih.gov/books/NBK538498/) - StatPearls / PubMed
3.  [The Endocrine System](https://www.hopkinsmedicine.org/health/conditions-and-diseases/anatomy-of-the-endocrine-system) - Johns Hopkins Medicine

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In This Entry

[Definition](#definition)[Also Known As](#also-known-as)[Key Facts](#key-facts)[How It Relates To Your Health](#health-relevance)[Related Terms](#related-terms)[Sources](#sources)

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[Insulin Resistance](/glossary/insulin-resistance)[Thyroid-Stimulating Hormone](/glossary/thyroid-stimulating-hormone)[Metabolic Syndrome](/glossary/metabolic-syndrome)[HbA1c](/glossary/hba1c)[Adrenal Fatigue](/glossary/adrenal-fatigue)[Blood Glucose](/glossary/blood-glucose)

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