Different types of hormones are secreted in the body, with different biological roles and functions.

A hormone (from the Greek participle “ὁρμῶ”, "to set in motion, urge on") is any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour. Hormones have diverse chemical structures, mainly of 3 classes: eicosanoids, steroids, and amino acid/protein derivatives (amines, peptides, and proteins). The glands that secrete hormones comprise the endocrine signaling system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell (autocrine or intracrine signalling) or nearby cells (paracrine signalling).

Hormones are used to communicate between organs and tissues for physiological regulation and behavioral activities, such as digestion, metabolism, respiration, tissue function, sensory perception, sleep, excretion, lactation, stress, growth and development, movement, reproduction, and mood.[1][2] Hormones affect distant cells by binding to specific receptor proteins in the target cell resulting in a change in cell function. When a hormone binds to the receptor, it results in the activation of a signal transduction pathway that typically activates gene transcription resulting in increased expression of target proteins; non-genomic effects are more rapid, and can be synergistic with genomic effects.[3] Amino acid–based hormones (amines and peptide or protein hormones) are water-soluble and act on the surface of target cells via second messengers; steroid hormones, being lipid-soluble, move through the plasma membranes of target cells (both cytoplasmic and nuclear) to act within their nuclei.

Hormone secretion may occur in many tissues. Endocrine glands are the cardinal example, but specialized cells in various other organs also secrete hormones. Hormone secretion occurs in response to specific biochemical signals from a wide range of regulatory systems. For instance, serum calcium concentration affects parathyroid hormone synthesis; blood sugar (serum glucose concentration) affects insulin synthesis; and because the outputs of the stomach and exocrine pancreas (the amounts of gastric juice and pancreatic juice) become the input of the small intestine, the small intestine secretes hormones to stimulate or inhibit the stomach and pancreas based on how busy it is. Regulation of hormone synthesis of gonadal hormones, adrenocortical hormones, and thyroid hormones is often dependent on complex sets of direct influence and feedback interactions involving the hypothalamic-pituitary-adrenal (HPA), -gonadal (HPG), and -thyroid (HPT) axes.

Upon secretion, certain hormones, including protein hormones and catecholamines, are water-soluble and are thus readily transported through the circulatory system. Other hormones, including steroid and thyroid hormones, are lipid-soluble; to allow for their widespread distribution, these hormones must bond to carrier plasma glycoproteins (e.g., thyroxine-binding globulin (TBG)) to form ligand-protein complexes. Some hormones are completely active when released into the bloodstream (as is the case for insulin and growth hormones), while others are prohormones that must be activated in specific cells through a series of activation steps that are commonly highly regulated. The endocrine system secretes hormones directly into the bloodstream, typically via fenestrated capillaries, whereas the exocrine system secretes its hormones indirectly using ducts. Hormones with paracrine function diffuse through the interstitial spaces to nearby target tissue.


Hormonal signaling involves the following steps:[4]

  1. Biosynthesis of a particular hormone in a particular tissue
  2. Storage and secretion of the hormone
  3. Transport of the hormone to the target cell(s)
  4. Recognition of the hormone by an associated cell membrane or intracellular receptor protein
  5. Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production. This is an example of a homeostatic negative feedback loop.
  6. Breakdown of the hormone.

Hormone producing cells are typically of a specialized cell type, residing within a particular endocrine gland, such as the thyroid gland, ovaries, and testes. Hormones exit their cell of origin via exocytosis or another means of membrane transport. The hierarchical model is an oversimplification of the hormonal signaling process. Cellular recipients of a particular hormonal signal may be one of several cell types that reside within a number of different tissues, as is the case for insulin, which triggers a diverse range of systemic physiological effects. Different tissue types may also respond differently to the same hormonal signal.

Other Languages
Afrikaans: Hormoon
Alemannisch: Hormon
العربية: هرمون
aragonés: Hormona
অসমীয়া: হ'ৰমন
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azərbaycanca: Hormonlar
বাংলা: হরমোন
Bân-lâm-gú: Ho͘-lú-bóng
башҡортса: Гормондар
беларуская: Гармоны
беларуская (тарашкевіца)‎: Гармоны
български: Хормон
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فارسی: هورمون
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मराठी: संप्रेरक
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မြန်မာဘာသာ: ဟော်မုန်း
Nederlands: Hormoon
नेपाली: हर्मोन
नेपाल भाषा: हर्मोन
日本語: ホルモン
Nordfriisk: Hormoon
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oʻzbekcha/ўзбекча: Gormonlar
ਪੰਜਾਬੀ: ਹਾਰਮੋਨ
پنجابی: ہارمون
پښتو: هورمون
português: Hormona
română: Hormon
русиньскый: Гормон
русский: Гормоны
Scots: Hormone
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sicilianu: Urmoni
Simple English: Hormone
سنڌي: هارمون
slovenčina: Hormón
slovenščina: Hormon
کوردی: ھۆرمۆن
српски / srpski: Хормони
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тыва дыл: Гормоннар
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اردو: ہارمون
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Tiếng Việt: Nội tiết tố
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吴语: 激素
ייִדיש: הארמאן
粵語: 賀爾蒙
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