Hormones: a plain-language reference
Hormones are signaling molecules released by glands of the endocrine system into the bloodstream, where they travel to tissues and organs and regulate processes such as metabolism, growth, reproduction, mood, and the stress response. This library explains each major hormone: what it is, where it is produced, what it does, and how it is measured in blood.
How hormones work
Most hormones operate through feedback loops. A gland (often the pituitary, directed by the hypothalamus in the brain) releases a stimulating hormone that tells a target gland to produce its own hormone; rising levels of that hormone then signal back to reduce further stimulation. Understanding these loops is the key to interpreting many hormone blood tests, because a result rarely means much in isolation.
Browse hormones
Testosterone: Functions, Levels & Testing
Plain-language guide to testosterone — what it is, where it is made, what it does, how levels are regulated, and how a blood test measures it.
Estradiol (Estrogen): Roles & Testing
Plain-language guide to estradiol — what it is, where it is made, what it does, how levels are regulated across the cycle, and how a blood test measures it.
Progesterone: Functions & Testing
Plain-language guide to progesterone — what it is, where it is made, what it does in the menstrual cycle and pregnancy, and how a blood test measures it.
Cortisol: The Stress Hormone Explained
Plain-language guide to cortisol — what it is, where it is made, what it does, how the daily rhythm and feedback loop work, and how a blood test measures it.
Thyroid Hormones: TSH, T4 & T3
Plain-language guide to thyroid hormones — what TSH, T4 and T3 are, where they are made, what they do, the feedback loop that controls them, and testing.
Insulin: Function & Blood Sugar Control
Plain-language guide to insulin — what it is, where it is made, how it controls blood sugar, how its release is regulated, and how it is measured in blood.
DHEA & DHEA-S: What They Do
Plain-language guide to DHEA and DHEA-S — what they are, where they are made, their role as hormone precursors, how they are regulated, and how they are tested.
Growth Hormone (GH) & IGF-1
Plain-language guide to growth hormone and IGF-1 — what they are, where they are made, what they do, how the feedback loop works, and how they are measured.
Prolactin: Functions & Testing
Plain-language guide to prolactin — what it is, where it is made, its role in milk production and beyond, how it is regulated, and how it is measured in blood.
Melatonin: The Sleep Hormone
Plain-language guide to melatonin — what it is, where it is made, how it signals night to the body, how light regulates it, and how it is measured.
Aldosterone: Blood Pressure & Salt Balance
Plain-language guide to aldosterone — what it is, where it is made, how it controls sodium, potassium, and blood pressure, how it is regulated, and measured.
Parathyroid Hormone (PTH) & Calcium Balance
Plain-language guide to parathyroid hormone (PTH) — what it is, where it is made, how it controls calcium and phosphate, how it is regulated, and measured.
ACTH (Adrenocorticotropic Hormone) Explained
Plain-language guide to ACTH — what adrenocorticotropic hormone is, where it is made, how it drives cortisol, how it is regulated, and how it is measured.
Oxytocin: Functions Explained Clearly
Plain-language guide to oxytocin — what it is, where it is made, its roles in labor, breastfeeding, and social bonding, how it is regulated, and measured.
Vitamin D: The Hormone-Like Vitamin
Plain-language guide to vitamin D — what it is, how the body makes and activates it, its role in calcium and bone, how it is regulated, and measured.
Calcitonin: Calcium Regulation Explained
Plain-language guide to calcitonin — what it is, where it is made, its role in calcium and bone, how it is regulated, and how a blood test measures it.
Glucagon: The Blood-Sugar-Raising Hormone
Plain-language guide to glucagon — what it is, where it is made, how it raises blood sugar, how its release is regulated, and how it is measured in blood.
Leptin: The Satiety Hormone Explained
Plain-language guide to leptin — what it is, where it is made, how it signals fullness and energy stores, how it is regulated, and how it is measured in blood.
Ghrelin: The Hunger Hormone Explained
Plain-language guide to ghrelin — what it is, where it is made, how it stimulates appetite, how its release is regulated, and how it is measured in blood.
Adrenaline (Epinephrine): Function Explained
Plain-language guide to adrenaline (epinephrine) — what it is, where it is made, its fight-or-flight role, how it is regulated, and how it is measured.
Norepinephrine: Function and Role Explained
Plain-language guide to norepinephrine — what it is, where it is made, its role in alertness and blood pressure, how it is regulated, and how it is measured.
Vasopressin (ADH): Water Balance Explained
Plain-language guide to vasopressin (antidiuretic hormone, ADH) — what it is, where it is made, how it controls water balance, regulation and testing.
Erythropoietin (EPO) Explained Clearly
Plain-language guide to erythropoietin (EPO) — what it is, where the kidneys make it, how it drives red blood cell production, regulation and testing.
Somatostatin Explained: The Off Switch
Plain-language guide to somatostatin — what it is, where it is made, how it acts as a braking hormone for the body, how it is regulated and measured.
GnRH (Gonadotropin-Releasing Hormone) Guide
Plain-language guide to GnRH — what it is, where it is made, how its pulses control reproductive hormones, how it is regulated and why it is rarely measured.
TRH (Thyrotropin-Releasing Hormone) Guide
Plain-language guide to TRH — what it is, where it is made, how it starts the thyroid hormone chain, how it is regulated and why it is rarely measured.
Sources
- MedlinePlus (U.S. National Library of Medicine). Hormones. https://medlineplus.gov/hormones.html
- Endocrine Society / Hormone Health Network. https://www.hormone.org/