Hormones in our body
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NIDDK endocrine system hormones overview
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Hormones are chemical messengers made by glands and tissues in the body. They travel through the blood and act only on cells that have the matching receptor. They help regulate growth, energy use, stress, sleep, reproduction, mood, blood sugar, and fluid balance. NIDDK notes that endocrine glands influence growth and development, metabolism, sexual function, and mood.
| Gland or tissue | Main hormones | Main role |
|---|---|---|
| Hypothalamus | Releasing hormones, ADH, oxytocin | Connects the brain and hormone system; regulates pituitary |
| Pituitary gland | Growth hormone, TSH, ACTH, LH, FSH, prolactin | Often called the “master gland”; controls other glands |
| Thyroid | T3, T4, calcitonin | Controls metabolic rate, heat production, growth |
| Parathyroid glands | Parathyroid hormone (PTH) | Controls calcium and phosphate balance |
| Pancreas | Insulin, glucagon | Maintains blood glucose level |
| Adrenal glands | Cortisol, aldosterone, adrenaline | Stress response, blood pressure, salt-water balance |
| Ovaries | Estrogen, progesterone | Menstrual cycle, pregnancy, female sexual development |
| Testes | Testosterone | Male sexual development and sperm production |
| Pineal gland | Melatonin | Sleep-wake rhythm |
| Kidneys | Erythropoietin, renin | Red blood cell production and blood-pressure regulation |
| Fat tissue and gut | Leptin, ghrelin, incretins | Appetite, body-weight and digestion signals |
How hormones work
- A gland releases a hormone into the bloodstream.
- The hormone reaches many tissues.
- Only target cells with the appropriate receptor respond.
- Feedback loops keep hormone levels balanced. For example, when thyroid hormone is high, the brain reduces signals that stimulate the thyroid.
Hormonal effects can be rapid, such as adrenaline increasing heart rate, or slower, such as growth hormone influencing protein production and growth. Hormone problems can occur when too much hormone is made, too little is made, or cells do not respond normally to it.
Medical Physiology describes endocrine signaling as blood-borne chemical communication to distant receptor-bearing target tissues.
Medical Physiology describes endocrine signaling as blood-borne chemical communication to distant receptor-bearing target tissues.
Explain the major hormones and their functions
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"Endocrine System"[MeSH Terms] AND hormones
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NIDDK endocrine glands hormones body functions overview
Major hormones and their functions
Hormones are chemical messengers released into the blood. They act on target cells with the correct receptors and help regulate metabolism, growth, reproduction, stress responses, sleep, and the balance of water and minerals. The endocrine system includes the pituitary, thyroid, adrenal glands, pancreas, and other hormone-producing tissues. NIDDK overview
1. Hypothalamus
Located in the brain, the hypothalamus links the nervous and endocrine systems. It controls the pituitary gland.
| Hormone | Main function |
|---|---|
| TRH, or thyrotropin-releasing hormone | Stimulates release of TSH, which controls the thyroid |
| CRH, or corticotropin-releasing hormone | Stimulates ACTH release, leading to cortisol production |
| GnRH, or gonadotropin-releasing hormone | Stimulates LH and FSH release for reproductive function |
| GHRH | Stimulates growth hormone release |
| Somatostatin | Inhibits growth hormone and TSH release |
| Dopamine | Inhibits prolactin release |
The hypothalamus also produces ADH and oxytocin, which are released from the posterior pituitary.
2. Pituitary gland
The pituitary is below the brain. It is often called the master gland because several of its hormones regulate other glands.
| Hormone | Main function |
|---|---|
| Growth hormone, GH | Promotes growth of bone and muscle; affects protein, fat, and glucose metabolism |
| Thyroid-stimulating hormone, TSH | Stimulates the thyroid gland to make T3 and T4 |
| Adrenocorticotropic hormone, ACTH | Stimulates the adrenal cortex to produce cortisol |
| Follicle-stimulating hormone, FSH | Supports egg development in ovaries and sperm production in testes |
| Luteinizing hormone, LH | Triggers ovulation and progesterone production; stimulates testosterone production in testes |
| Prolactin | Stimulates milk production after childbirth |
| Antidiuretic hormone, ADH or vasopressin | Reduces urine production by increasing water reabsorption in kidneys; helps maintain blood pressure |
| Oxytocin | Causes uterine contractions during labor and milk ejection during breastfeeding |
3. Thyroid and parathyroid glands
| Hormone | Produced by | Main function |
|---|---|---|
| T4, thyroxine, and T3, triiodothyronine | Thyroid gland | Increase metabolic rate, heat production, growth, brain development, and heart activity |
| Calcitonin | Thyroid gland | Helps lower blood calcium, although its role in adults is limited |
| Parathyroid hormone, PTH | Parathyroid glands | Raises blood calcium by acting on bone, kidneys, and indirectly the intestine |
Thyroid hormones affect how nearly every organ uses energy, including the heart. NIDDK thyroid information
4. Pancreatic hormones
The pancreas contains endocrine cell clusters called islets.
| Hormone | Main function |
|---|---|
| Insulin | Lowers blood glucose by helping cells take up glucose and promoting storage as glycogen and fat |
| Glucagon | Raises blood glucose by stimulating the liver to release glucose |
| Somatostatin | Reduces release of insulin, glucagon, and several digestive hormones |
Insulin and glucagon work in opposite directions to keep blood glucose within a healthy range.
5. Adrenal gland hormones
Each adrenal gland sits above a kidney. It has an outer cortex and an inner medulla.
| Hormone | Part of adrenal | Main function |
|---|---|---|
| Cortisol | Cortex | Helps the body respond to stress; supports blood glucose, blood pressure, and metabolism; also reduces inflammation |
| Aldosterone | Cortex | Increases sodium and water retention by kidneys and promotes potassium excretion, helping maintain blood pressure |
| Adrenal androgens, such as DHEA | Cortex | Contribute to pubic and underarm hair and can contribute to sex-hormone effects |
| Adrenaline, epinephrine | Medulla | Rapid “fight-or-flight” response: raises heart rate, blood pressure, and blood glucose |
| Noradrenaline, norepinephrine | Medulla | Mainly constricts blood vessels and raises blood pressure during stress |
6. Reproductive hormones
| Hormone | Main source | Main function |
|---|---|---|
| Estrogen | Ovaries, placenta | Female sexual development; menstrual-cycle regulation; bone health |
| Progesterone | Ovary after ovulation, placenta | Prepares and maintains the uterine lining for pregnancy |
| Testosterone | Testes, smaller amounts from ovaries/adrenals | Male sexual development, sperm production, muscle and bone maintenance |
| Inhibin | Ovaries and testes | Reduces FSH release |
| Human chorionic gonadotropin, hCG | Placenta in pregnancy | Maintains the ovarian corpus luteum early in pregnancy; detected by pregnancy tests |
7. Pineal hormone
| Hormone | Main function |
|---|---|
| Melatonin | Helps regulate the sleep-wake cycle and circadian rhythm; secretion generally rises in darkness |
8. Kidney, heart, liver, and fat-tissue hormones
| Hormone | Main source | Main function |
|---|---|---|
| Erythropoietin, EPO | Kidneys | Stimulates bone marrow to make red blood cells |
| Renin | Kidneys | Begins a hormone system that helps regulate blood pressure and fluid balance |
| Calcitriol, active vitamin D | Kidneys | Increases intestinal calcium and phosphate absorption |
| Atrial natriuretic peptide, ANP | Heart | Encourages sodium and water loss, helping lower blood volume and pressure |
| Insulin-like growth factor 1, IGF-1 | Liver | Mediates many growth-promoting effects of growth hormone |
| Leptin | Fat tissue | Signals energy stores to the brain and contributes to appetite regulation |
| Ghrelin | Stomach | Stimulates hunger, especially before meals |
Key idea: negative feedback
Most hormone systems use negative feedback. When the body has enough of a hormone, it reduces the signals that stimulate further production.
For example:
Hypothalamus → TRH → Pituitary → TSH → Thyroid → T3/T4
When T3 and T4 levels rise sufficiently, they reduce TRH and TSH release. This prevents excessive thyroid-hormone production. Problems arise when hormone production is too high, too low, or target cells become resistant to the hormone.
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