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A hormone (from the
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
participle , "setting in motion") is any member of a class of
signaling molecules In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (biology), cells and coordinates multiple-cell actions. A signal is an entity that codes or conveys information. Biolo ...
in
multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biol ...
s, that are transported to distant organs to regulate
physiology Physiology (; ) is the scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, know ...
and
behavior Behavior (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English ...
. Hormones are required for the correct development of
animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been —of which around 1 million are —b ...

animal
s,
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s and
fungi A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as ...

fungi
. The lax definition of a hormone (as a signalling molecule that acts distant from its site of production) means that many different classes of molecule can be defined as hormones. Among the substances that can be considered hormones, are
eicosanoid Eicosanoids are lipid signaling, signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, 20 carbon units in length. Eicosanoids are ...
s (e.g.
prostaglandin The prostaglandins (PG) are a group of physiologically active lipid In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecul ...
s and
thromboxane Thromboxane is a member of the family of lipids In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular ...
s),
steroid A steroid is a biologically active organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the prope ...

steroid
s (e.g.
oestrogen Estrogens or oestrogens, are a class of natural or synthetic sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hor ...

oestrogen
and
brassinosteroid Brassinosteroids (BRs) are a class of polyhydroxysteroids that have been recognized as a sixth class of plant hormones Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or ce ...
),
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
derivatives (e.g.
epinephrine Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in ...

epinephrine
and
auxin Auxins (plural of auxin ) are a class of plant hormone Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (bio ...

auxin
),
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
/ peptides (e.g.
insulin Insulin (, from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republi ...

insulin
and
CLE peptideCLE peptides (CLAVATA3/Embryo Surrounding Region-Related) are a group of peptide Peptides (from Greek language πεπτός, ''peptós'' "digested"; derived from πέσσειν, ''péssein'' "to digest") are short chains of amino acids linked by pe ...
s) and
gas Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

gas
es (e.g
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science C ...

ethylene
and
nitrous oxide Nitrous oxide, commonly known as laughing gas or nitrous, is a chemical compound, an Nitrogen oxide, oxide of nitrogen with the Chemical formula, formula . At room temperature, it is a colourless Flammability#Definitions, non-flammable gas, ...
). Hormones are used to communicate between
organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
and tissues. In
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s, hormones are responsible for the regulation of many
physiological Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
processes and
behavioral Behavior (American English) or behaviour (British English; American and British English spelling differences#-our, -or, see spelling differences) is the Action (philosophy), actions and mannerisms made by individuals, organisms, systems or Arti ...
activities such as
digestion Digestion is the breakdown of large insoluble food Food is any substance consumed to provide nutritional Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to liv ...
,
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining ...

metabolism
,
respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellular ...
,
sensory perception Perception (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the powe ...
,
sleep Sleep is a naturally recurring state of mind and body, characterized by altered consciousness Consciousness, at its simplest, is or of internal and external existence. Despite millennia of analyses, definitions, explanations and deba ...

sleep
,
excretion Excretion is a process in which metabolic waste Metabolic wastes or excrements are Chemical substance, substances left over from metabolism, metabolic processes (such as cellular respiration) which cannot be used by the organism (they are surplus ...
,
lactation Lactation describes the secretion of milk Milk is a nutrient-rich liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they a ...

lactation
, stress induction, growth and development,
movement Movement may refer to: Common uses * Movement (clockwork), the internal mechanism of a timepiece * Motion (physics), commonly referred to as movement Arts, entertainment, and media Literature * Movement (short story), "Movement", a shor ...
,
reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

reproduction
, and mood manipulation. In plants, hormones modulate almost all aspects of development, from
germination seedlings, three days after germination Germination is the process by which an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell t ...

germination
to
senescence Ann Pouder American supercentenarians are citizens or residents of the United States who have attained or surpassed 110 years of age. , the Gerontology Research Group The Gerontology Research Group (GRG) is a global group of researchers in v ...

senescence
. Hormones affect distant cells by binding to specific
receptor
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 Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation residue Protein phosphorylation is a reversible post-translational ...
pathway that typically activates gene transcription, resulting in increased
expression
expression
of target proteins. Hormones can also act in rapid, non-genomic pathways that can be
synergistic Synergy is an interaction or cooperation giving rise to a whole that is greater than the simple sum of its parts. The term ''synergy'' comes from the Attic Greek Attic Greek is the Greek language, Greek dialect of the regions of ancient Greec ...
with genomic effects. Water-soluble hormones (such as peptides and amines) generally act on the surface of target cells via
second messengers Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules—the first messengers. (Intracellular signals, a non-local form or cell signaling, encompassing both first mes ...
. Lipid soluble hormones, (such as steroids) generally pass through the plasma membranes of target cells (both
cytoplasmic In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...

cytoplasmic
and
nuclear
nuclear
) to act within their
nuclei ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nuclei
. A notable exception to this are brassinosteroids in plants, which despite being lipid soluble, still bind to their receptor at the cell surface. In vertebrates,
endocrine gland Endocrine glands are ductless glands of the endocrine system The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating dista ...
s are specialized organs that
secreteSecretion is the movement of material from one point to another, such as a secreted chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up sp ...
hormones into the
endocrine signaling system
endocrine signaling system
. Hormone secretion occurs in response to specific biochemical signals and is often subject to negative feedback regulation. For instance, high
blood sugar The blood sugar level, blood sugar concentration, or blood glucose level is the concentration of glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water ...
(serum glucose concentration) promotes
insulin Insulin (, from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republi ...

insulin
synthesis. Insulin then acts to reduce glucose levels and maintain
homeostasis In , homeostasis is the state of steady internal, , and conditions maintained by . This is the condition of optimal functioning for the organism and includes many variables, such as and , being kept within certain pre-set limits (homeostatic r ...
, leading to reduced insulin levels. Upon secretion, water soluble hormones are readily transported through the circulatory system. Lipid-soluble hormones must bond to carrier plasma glycoproteins (e.g.,
thyroxine-binding globulin Thyroxine-binding globulin (TBG) is a globulin The globulins are a family of globular protein 300px, 3-dimensional structure of hemoglobin, a globular protein. Globular proteins or spheroproteins are spherical ("globe-like") protein Protei ...
(TBG)) to form
ligand In coordination chemistry A coordination complex consists of a central atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...
-protein complexes. Completely active hormones can be released into the bloodstream (as seen in insulin and growth hormones), but some travel as prohormones that must be activated in specific cells through a series of activation steps that are commonly highly regulated. The
endocrine system The endocrine system is a messenger system comprising feedback loops of the hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported ...

endocrine system
secreteSecretion is the movement of material from one point to another, such as a secreted chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up sp ...
s hormones directly into the
bloodstream The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex biological network, network which connects several biologically ...
, typically via
fenestrated capillaries
fenestrated capillaries
, whereas the
exocrine system Exocrine glands are gland A gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellu ...
secretes its hormones indirectly using ducts. Hormones with
paracrineParacrine signaling is form of cell signaling or cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. Signaling molecules known as paracrine factors diffuse over a rel ...
function diffuse through the
interstitial space An interstitial space or interstice is a space between structures or objects. In particular, interstitial may refer to: Biology * Interstitial cell tumor * Interstitial cell, any cell that lies between other cells * Interstitial collagenase, e ...
s to nearby target tissue. Plants lack specialized organs for the secretion of hormones, although there is spacial distribution of hormone production. For example, the hormone auxin is produced mainly at the tips of young
leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

leaves
and in the
shoot apical meristem The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division Cell division is the process by which a parent Cell (biology), cell divides into two or more daughter cells. C ...
. The lack of specialised glands means that the main site of hormone production can change throughout the life of a plant, and the site of production is dependent on the plant's age and environment.


Introduction and overview

Hormonal signaling involves the following steps: #
Biosynthesis Biosynthesis is a multi-step, enzyme-Catalysis, catalyzed process where substrate (chemistry), substrates are converted into more complex Product (chemistry), products in living organisms. In biosynthesis, simple Chemical compound, compounds are mod ...

Biosynthesis
of a particular hormone in a particular tissue. # Storage and
secretion Secretion is the movement of material from one point to another, such as a secreted from a or . In contrast, , is the removal of certain substances or waste products from a cell or organism. The classical mechanism of cell secretion is via secret ...
of the hormone. # Transport of the hormone to the target cell(s). # Recognition of the hormone by an
associated cell membrane
associated cell membrane
or
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemic ...
receptor
receptor
protein. # Relay and amplification of the received hormonal signal via a
signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation residue Protein phosphorylation is a reversible post-translational ...
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 downregulation in hormone production. This is an example of a
homeostatic In biology, homeostasis is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning for the organism and includes many variables, such ...
negative feedback loop AB is negative. Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, wh ...

negative feedback loop
. # Breakdown of the hormone. Hormone producing cells are found in the
endocrine glands Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, Ovary, ovaries, Testicle, tes ...

endocrine glands
, such as the
thyroid gland The thyroid, or thyroid gland, is an endocrine gland Endocrine glands are ductless glands of the endocrine system The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organis ...

thyroid gland
,
ovaries The ovary is an organ found in the female reproductive system 300px, 1. Labia_majora.html"_;"title="Vulva: 2. Labia_majora">Vulva: 2. Labia_majora; 3. Labia_minora; 4. Vulval_vestibule.html" "title="Labia_minora.html ...

ovaries
, and
testes Testicle or testis (plural testes) is the or in all animals, including humans. It is to the female . The functions of the testes are to produce both and , primarily . Testosterone release is controlled by the anterior pituitary , whereas ...

testes
.
Exocytosis Image:Synapse diag1.svg, 300px, Exocytosis of neurotransmitters into a synapse from neuron A to neuron B. Exocytosis () is a form of active transport and solvent drag, bulk transport in which a cell transports molecules (e.g., neurotransmitters an ...
and other methods of
membrane transport In cellular biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...

membrane transport
are used to secrete hormones when the endocrine glands are signaled. The hierarchical model is an
oversimplification The fallacy of the single cause, also known as complex cause, causal oversimplification, causal reductionism, and reduction fallacy, is an informal fallacy Informal fallacies are a type of incorrect argument In logic Logic (from Ancient Gre ...
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 Insulin (, from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republi ...

insulin
, which triggers a diverse range of systemic physiological effects. Different tissue types may also respond differently to the same hormonal signal.


Discovery


Arnold Adolph Berthold (1849)

Arnold Adolph Berthold Arnold Adolph Berthold (also Arnold Adolf Berthold) (26 February 1803, in Soest – 3 January 1861, in Göttingen) was a German Science, scientist, most notably a Physiology, physiologist and Zoology, zoologist . He is best known in modern scienc ...

Arnold Adolph Berthold
was a German
physiologist Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
and
zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological class ...
, who, in 1849, had a question about the function of the
testes Testicle or testis (plural testes) is the or in all animals, including humans. It is to the female . The functions of the testes are to produce both and , primarily . Testosterone release is controlled by the anterior pituitary , whereas ...

testes
. He noticed in castrated roosters that they did not have the same sexual behaviors as
rooster The chicken (''Gallus gallus domesticus'') is a domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another ...

rooster
s with their testes intact. He decided to run an experiment on male roosters to examine this phenomenon. He kept a group of roosters with their testes intact, and saw that they had normal sized wattles and combs (secondary sexual organs), a normal crow, and normal sexual and aggressive behaviors. He also had a group with their testes surgically removed, and noticed that their secondary sexual organs were decreased in size, had a weak crow, did not have sexual attraction towards females, and were not aggressive. He realized that this organ was essential for these behaviors, but he did not know how. To test this further, he removed one testis and placed it in the abdominal cavity. The roosters acted and had normal physical
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...

anatomy
. He was able to see that location of the testes does not matter. He then wanted to see if it was a
genetic
genetic
factor that was involved in the testes that provided these functions. He transplanted a testis from another rooster to a rooster with one testis removed, and saw that they had normal behavior and physical anatomy as well. Berthold determined that the location or genetic factors of the testes do not matter in relation to sexual organs and behaviors, but that some
chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which ...

chemical
in the testes being secreted is causing this phenomenon. It was later identified that this factor was the hormone
testosterone Testosterone is the primary sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two cl ...
.


Charles and Francis Darwin (1880)

Although known primarily for his work on the
Theory of Evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are passed on from parent to offsp ...

Theory of Evolution
,
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all sp ...

Charles Darwin
was also keenly interested in plants. Through the 1870s, he and his son
Francis Francis may refer to: People *Pope Francis Pope Francis ( la, Franciscus; it, Francesco; es, link=no, Francisco; born Jorge Mario Bergoglio, 17 December 1936) is the head of the Catholic Church The Catholic Church, often referred to ...
studied the movement of plants towards light. They were able to show that light is perceived at the tip of a young stem (the
coleoptile Schematic image of wheat coleoptile (above) and flag leaf (below). Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclo ...

coleoptile
), whereas the bending occurs lower down the stem. They proposed that a 'transmissible substance' communicated the direction of light from the tip down to the stem. The idea of a 'transmissible substance' was initially dismissed by other plant biologists, but their work later led to the discovery of the first plant hormone. In the 1920s Dutch scientist
Frits Warmolt Went:''For his father, also a botanist, see Frits the father Went.'' Frits Warmolt Went (May 18, 1903 – May 1, 1990) was a Dutch biologist whose 1928 experiment demonstrated the existence of auxin Auxins (plural of auxin ) are a class of plant horm ...
and Russian scientist Nikolai Cholodny (working independently of each other) conclusively showed that asymmetric accumulation of a growth hormone was responsible for this bending. In 1933 this hormone was finally isolated by Kögl, Haagen-Smit and Erxleben and given the name '
auxin Auxins (plural of auxin ) are a class of plant hormone Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (bio ...

auxin
'.


Bayliss and Starling (1902)

William Bayliss Sir William Maddock Bayliss (2 May 1860 – 27 August 1924) was an English physiologist Physiology (; ) is the scientific study of Function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a Branches o ...

William Bayliss
and
Ernest Starling Ernest Henry Starling (17 April 1866 – 2 May 1927) was a British physiologist Physiology (; ) is the scientific study of Function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a Branches of science, sub ...

Ernest Starling
, a
physiologist Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
and
biologist A biologist is a professional who has specialized knowledge in the field of biology, understanding the underlying mechanisms that govern the functioning of biological systems within fields such as health, technology and the Biophysical environm ...
, respectively, wanted to see if the
nervous system In biology, the classical doctrine of the nervous system determines that it is a Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting action potential, signals ...

nervous system
had an impact on the
digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus which includes all the organs of th ...
. They knew that the
pancreas The pancreas is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ ...

pancreas
was involved in the secretion of digestive fluids after the passage of food from the
stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilated structure and functions as a vital organ. In the digestive system the stomach is involved in the second phase of digestion, ...

stomach
to the
intestines The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syst ...
, which they believed to be due to the nervous system. They cut the nerves to the pancreas in an animal model and discovered that it was not nerve impulses that controlled secretion from the pancreas. It was determined that a factor secreted from the intestines into the
bloodstream The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex biological network, network which connects several biologically ...
was stimulating the pancreas to secrete digestive fluids. This factor was named
secretin Secretin is a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior. Hor ...
: a hormone, although the term hormone was not coined until 1905 by Starling.


Types of signaling

Hormonal effects are dependent on where they are released, as they can be released in different manners. Not all hormones are released from a cell and into the blood until it binds to a receptor on a target. The major types of hormone signaling are:


Chemical classes

As hormones are defined functionally, not structurally, they may have diverse chemical structures. Hormones occur in
multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biol ...
s (
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s,
animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been —of which around 1 million are —b ...

animal
s,
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
,
brown algae The brown algae (singular: alga), comprising the class (biology), class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Most brown algae live in marine enviro ...
, and
red algae Red algae, or Rhodophyta ( , ; ), are one of the oldest groups of eukaryotic algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organism ...

red algae
). These compounds occur also in
unicellular organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Org ...
s, and may act as
signaling molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cells and coordinates multiple-cell actions. A signal is an entity that codes or conveys information Information ...
s however there is no agreement that these molecules can be called hormones.


Vertebrates


Invertebrates

Compared with vertebrates,
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s and
crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, amphipoda, amphipods and mantis shrimp. The ...
s possess a number of structurally unusual hormones such as the
juvenile hormoneJuvenile hormones (JHs) are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. The first discovery of a JH was by Vincent Wigglesworth. JHs regulate development, reproduction, diapause, and polyphenisms. In in ...
, a
sesquiterpenoid '' Phallus indusiatus'', in Cooktown, Queensland, Australia, which produces two novel sesquiterpenes">Cooktown,_Queensland.html" ;"title="Phallus indusiatus'', in Cooktown, Queensland">Phallus indusiatus'', in Cooktown, Queensland, Australia, which ...
.


Plants

Examples include
abscisic acid Abscisic acid (ABA) is a plant hormone Plant hormones (also known as phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, fr ...

abscisic acid
,
auxin Auxins (plural of auxin ) are a class of plant hormone Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (bio ...

auxin
,
cytokinin Image:Zeatin.png, 122px, The cytokinin zeatin is named after the genus of corn, ''Teosinte, Zea''. Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in ...
,
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science C ...
, and
gibberellin Gibberellins (GAs) are plant hormone Plant hormones (also known as phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from ...
.


Receptors

Most hormones initiate a cellular response by initially binding to either or
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemic ...
s. A cell may have several different receptor types that recognize the same hormone but activate different
signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation residue Protein phosphorylation is a reversible post-translational ...
pathways, or a cell may have several different receptors that recognize different hormones and activate the same biochemical pathway. Receptors for most
peptide Peptides (from Greek language Greek (modern , romanized: ''Elliniká'', Ancient Greek, ancient , ''Hellēnikḗ'') is an independent branch of the Indo-European languages, Indo-European family of languages, native to Greece, Cyprus, Albania, ...
as well as many
eicosanoid Eicosanoids are lipid signaling, signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, 20 carbon units in length. Eicosanoids are ...
hormones are embedded in the
plasma membrane cell membrane vs. Prokaryotes A prokaryote () is a single-celled organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organ ...
at the surface of the cell and the majority of these receptors belong to the
G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily-related prot ...
(GPCR) class of seven
alpha helix The alpha helix (α-helix) is a common motif Motif may refer to: General concepts * Motif (chess composition), an element of a move in the consideration of its purpose * Motif (folkloristics), a recurring element that creates recognizable patte ...

alpha helix
transmembrane Image:Polytopic membrane protein.png, 400px, Schematic representation of transmembrane proteins: 1) a single transmembrane α-helix (bitopic membrane protein). 2) a polytopic transmembrane α-helical protein. 3) a polytopic transmembrane β-sheet pr ...

transmembrane
proteins. The interaction of hormone and receptor typically triggers a cascade of secondary effects within the
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
of the cell, described as
signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation residue Protein phosphorylation is a reversible post-translational ...
, often involving
phosphorylation In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, ...

phosphorylation
or dephosphorylation of various other cytoplasmic proteins, changes in
ion channel Ion channels are pore-forming membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane ...

ion channel
permeability, or increased concentrations of intracellular molecules that may act as
secondary messengers Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules—the first messengers. (Intracellular signals, a non-local form or cell signaling, encompassing both first mes ...
(e.g.,
cyclic AMP Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes. cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transd ...
). Some protein hormones also interact with
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemic ...
receptors located in the
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
or
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nucleus
by an
intracrine Intracrine refers to a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavi ...
mechanism. For
steroid A steroid is a biologically active organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the prope ...
or
thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connected by a thin band of Connective tissue, tissue cal ...
hormones, their
receptors Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ne ...
are located inside the cell within the
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
of the target cell. These receptors belong to the
nuclear receptor In the field of molecular biology, nuclear receptors are a class of proteins found within cells that are responsible for sensing Steroid hormone, steroid and Thyroid hormone, thyroid hormones and certain other molecules. In response, these recep ...
family of ligand-activated
transcription factor In molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, m ...
s. To bind their receptors, these hormones must first cross the cell membrane. They can do so because they are lipid-soluble. The combined hormone-receptor
complex The UCL Faculty of Mathematical and Physical Sciences is one of the 11 constituent faculties of University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public university, Public rese ...
then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific
DNA sequences A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, ...
, regulating the expression of certain
genes In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
, and thereby increasing the levels of the proteins encoded by these genes. However, it has been shown that not all steroid receptors are located inside the cell. Some are associated with the
plasma membrane cell membrane vs. Prokaryotes A prokaryote () is a single-celled organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organ ...
.


Effects in humans

Hormones have the following effects on the body: *stimulation or inhibition of growth *wake-sleep cycle and other
circadian rhythm A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogenou ...

circadian rhythm
s *
mood swing A mood swing is an extreme or rapid change in mood. Such mood swings can play a positive part in promoting problem solving and in producing flexible forward planning. However, when mood swings are so strong that they are disruptive, they may be ...
s *induction or suppression of
apoptosis Apoptosis (from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ) ...

apoptosis
(programmed cell death) *activation or inhibition of the
immune system The immune system is a network of biological processes that protects an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biolog ...
*regulation of
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining ...

metabolism
*preparation of the body for
mating In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

mating
,
fighting Combat (French language, French for ''fight'') is a purposeful violence, violent conflict meant to physically harm or kill the opposition. Combat may be armed (using weapons) or unarmed (Hand-to-hand combat, not using weapons). Combat is sometime ...

fighting
, fleeing, and other activity *preparation of the body for a new phase of life, such as
puberty Puberty is the process of physical changes through which a child Biologically, a child (plural children) is a human Humans (''Homo sapiens'') are the most abundant and widespread species In biology Biology is the natur ...

puberty
,
parenting Parenting or child rearing promotes and supports the physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia ...
, and
menopause Menopause, also known as the climacteric, is the time in women's lives when menstrual periods stop permanently, and they are no longer able to bear children. Menopause usually occurs between the age of 48 and 52. Medical professionals often ...
*control of the reproductive cycle *hunger cravings A hormone may also regulate the production and release of other hormones. Hormone signals control the internal environment of the body through
homeostasis In , homeostasis is the state of steady internal, , and conditions maintained by . This is the condition of optimal functioning for the organism and includes many variables, such as and , being kept within certain pre-set limits (homeostatic r ...
.


Regulation

The rate of hormone biosynthesis and secretion is often regulated by a
homeostatic In biology, homeostasis is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning for the organism and includes many variables, such ...
negative feedback AB is negative. Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether cau ...
control mechanism. Such a mechanism depends on factors that influence the
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining ...

metabolism
and
excretion Excretion is a process in which metabolic waste Metabolic wastes or excrements are Chemical substance, substances left over from metabolism, metabolic processes (such as cellular respiration) which cannot be used by the organism (they are surplus ...
of hormones. Thus, higher hormone concentration alone cannot trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an "effect" of the hormone. Hormone secretion can be stimulated and inhibited by: *Other hormones (''stimulating''- or ''releasing'' -hormones) *Plasma concentrations of ions or nutrients, as well as binding
globulin The globulins are a family of globular protein 300px, 3-dimensional structure of hemoglobin, a globular protein. Globular proteins or spheroproteins are spherical ("globe-like") protein Proteins are large biomolecules or macromolecules that ...
s *
Neuron A neuron or nerve cell is an electrically excitable cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or re ...

Neuron
s and mental activity *Environmental changes, e.g., of light or temperature One special group of hormones is the
tropic hormone Tropic hormones are hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior ...
s that stimulate the hormone production of other
endocrine glands Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, Ovary, ovaries, Testicle, tes ...

endocrine glands
. For example,
thyroid-stimulating hormone Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the nec ...
(TSH) causes growth and increased activity of another endocrine gland, the
thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connected by a thin band of Connective tissue, tissue cal ...

thyroid
, which increases output of
thyroid hormone File:Thyroid_system.svg, upright=1.5, The thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connec ...
s. To release active hormones quickly into the
circulation Circulation may refer to: Science and technology * Atmospheric circulation, the large-scale movement of air * Circulation (physics), the path integral of the fluid velocity around a closed curve in a fluid flow field * Circulatory system, a biolo ...
, hormone biosynthetic cells may produce and store biologically inactive hormones in the form of pre- or
prohormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior Behavior (American Eng ...
s. These can then be quickly converted into their active hormone form in response to a particular stimulus.
Eicosanoid Eicosanoids are lipid signaling, signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, 20 carbon units in length. Eicosanoids are ...
s are considered to act as local hormones. They are considered to be "local" because they possess specific effects on target cells close to their site of formation. They also have a rapid degradation cycle, making sure they do not reach distant sites within the body. Hormones are also regulated by receptor agonists. Hormones are ligands, which are any kinds of molecules that produce a signal by binding to a receptor site on a protein. Hormone effects can be inhibited, thus regulated, by competing ligands that bind to the same target receptor as the hormone in question. When a competing ligand is bound to the receptor site, the hormone is unable to bind to that site and is unable to elicit a response from the target cell. These competing ligands are called antagonists of the hormone.


Therapeutic use

Many hormones and their
structural A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A sy ...
and functional analogs are used as
medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, therapy, treat, or preventive medicine, prevent disease. Drug therapy (pharmacotherapy) ...

medication
. The most commonly prescribed hormones are
estrogen Estrogens or oestrogens, are a class of natural or synthetic s responsible for the development and regulation of the female and s. There are three major estrogens that have estrogenic hormonal activity: (E1), (E2), and (E3). Estradiol, an ...

estrogen
s and
progestogen Progestogens, also sometimes written progestagens or gestagens, are a class of natural or synthetic steroid hormone A steroid hormone is a steroid , hypothetical a steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 c ...
s (as methods of
hormonal contraception Hormonal contraception refers to birth control methods that act on the endocrine system. Almost all methods are composed of steroid hormones, although in India one selective estrogen receptor modulator is marketed as a contraceptive. The original h ...
and as HRT),
thyroxine File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones triiodothyronine, T3 and T4 rect 376 268 820 433 Thyroid-stimulating hormone rect 411 200 849 266 Thyrotropin-releasing hormone rect 297 168 502 200 Hypothalamus rec ...

thyroxine
(as
levothyroxine Levothyroxine, also known as -thyroxine, is a manufactured form of the thyroid hormone File:Thyroid_system.svg, upright=1.5, The thyroid The thyroid, or thyroid gland, is an endocrine gland in the neck consisting of two connected lobes. ...
, for
hypothyroidism Hypothyroidism (also called ''underactive thyroid'', ''low thyroid'' or ''hypothyreosis'') is a disorder of the endocrine system in which the thyroid gland The thyroid, or thyroid gland, is an endocrine gland in the neck consisting of two ...

hypothyroidism
) and
steroid A steroid is a biologically active organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the prope ...

steroid
s (for
autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of differe ...

autoimmune disease
s and several respiratory disorders).
Insulin Insulin (, from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republi ...

Insulin
is used by many
diabetics Diabetes mellitus (DM), commonly known as diabetes, is a group of metabolic disorders characterized by a hyperglycemia, high blood sugar level over a prolonged period of time. Symptoms often include frequent urination, Polydipsia, increased thirs ...
. Local preparations for use in
otolaryngology Otorhinolaryngology ( ; abbreviated ORL; also called otolaryngology; other terms include otolaryngology–head and neck surgery (ORL–H&N, OHNS) and ear, nose, and throat, often called ENT) is a surgical subspecialty within medicine that de ...
often contain
pharmacologic Pharmacology is a branch of medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment or Palliative ...
equivalents of
adrenaline Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate p ...

adrenaline
, while
steroid A steroid is a biologically active organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the prope ...

steroid
and
vitamin D Vitamin D is a group of fat-soluble secosteroid 250px, The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield D vitamins. A secosteroid () is a type of steroid , hypothetical a steroid with ...
creams are used extensively in
dermatological Dermatology is the branch of medicine dealing with the skin.''Random House Webster's Unabridged Dictionary.'' Random House, Inc. 2001. Page 537. . It is a speciality with both medical and surgical aspects. A List of dermatologists, dermatologist ...
practice. A "pharmacologic dose" or "supraphysiological dose" of a hormone is a medical usage referring to an amount of a hormone far greater than naturally occurs in a healthy body. The effects of pharmacologic doses of hormones may be different from responses to naturally occurring amounts and may be therapeutically useful, though not without potentially adverse side effects. An example is the ability of pharmacologic doses of
glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroid Corticosteroids are a class of steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: cor ...
s to suppress
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
.


Hormone-behavior interactions

At the neurological level, behavior can be inferred based on hormone concentration, which in turn are influenced by hormone-release patterns; the numbers and locations of hormone receptors; and the efficiency of hormone receptors for those involved in gene transcription. Hormone concentration does not incite behavior, as that would undermine other external stimuli; however, it influences the system by increasing the probability of a certain event to occur. Not only can hormones influence behavior, but also behavior and the environment can influence hormone concentration. Thus, a feedback loop is formed, meaning behavior can affect hormone concentration, which in turn can affect behavior, which in turn can affect hormone concentration, and so on. For example, hormone-behavior feedback loops are essential in providing constancy to episodic hormone secretion, as the behaviors affected by episodically secreted hormones directly prevent the continuous release of said hormones. Three broad stages of reasoning may be used to determine if a specific hormone-behavior interaction is present within a system: *The frequency of occurrence of a hormonally dependent behavior should correspond to that of its hormonal source. *A hormonally dependent behavior is not expected if the hormonal source (or its types of action) is non-existent. *The reintroduction of a missing behaviorally dependent hormonal source (or its types of action) is expected to bring back the absent behavior.


Comparison with neurotransmitters

There are various clear distinctions between hormones and
neurotransmitter A neurotransmitter is a signaling molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cells and coordinates multiple-cell actions. A signal is an entity that ...
s: *A hormone can perform functions over a larger spatial and temporal scale than can a neurotransmitter, which often acts in micrometer-scale distances. *Hormonal signals can travel virtually anywhere in the circulatory system, whereas neural signals are restricted to pre-existing nerve tracts. *Assuming the travel distance is equivalent, neural signals can be transmitted much more quickly (in the range of milliseconds) than can hormonal signals (in the range of seconds, minutes, or hours). Neural signals can be sent at speeds up to 100 meters per second. *Neural signalling is an all-or-nothing (digital) action, whereas hormonal signalling is an action that can be continuously variable as it is dependent upon hormone concentration. Neurohormones are a type of hormone that share a commonality with neurotransmitters. They are produced by endocrine cells that receive input from neurons, or neuroendocrine cells. Both classic hormones and neurohormones are secreted by endocrine tissue; however, neurohormones are the result of a combination between endocrine reflexes and neural reflexes, creating a neuroendocrine pathway. While endocrine pathways produce chemical signals in the form of hormones, the neuroendocrine pathway involves the electrical signals of neurons. In this pathway, the result of the electrical signal produced by a neuron is the release of a chemical, which is the neurohormone. Finally, like a classic hormone, the neurohormone is released into the bloodstream to reach its target.


Binding proteins

Hormone transport and the involvement of binding proteins is an essential aspect when considering the function of hormones. The formation of a complex with a binding protein has several benefits: the effective half-life of the bound hormone is increased, and a reservoir of bound hormones is created, which evens the variations in concentration of unbound hormones (bound hormones will replace the unbound hormones when these are eliminated). An example of the usage of hormone-binding proteins is in the thyroxine-binding protein which carries up to 80% of all thyroxine in the body, a crucial element in regulating the metabolic rate.


See also

*
Autocrine signalingAutocrine signaling is a form of cell signaling In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inter ...
*
Cytokine Cytokines are a broad and loose category of small s (~5–25 ) important in . Cytokines are s and cannot cross the of cells to enter the . Cytokines have been shown to be involved in , and as . Their definite distinction from is still part o ...

Cytokine
*
Endocrine disease Endocrine diseases are disorders of the endocrine system The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant ta ...
*
Endocrine system The endocrine system is a messenger system comprising feedback loops of the hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported ...

Endocrine system
*
Endocrinology Endocrinology (from ''endocrine system, endocrine'' + ''wikt:-logy#Suffix, -ology'') is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. It is also concerned with the ...
* Environmental hormones *
Growth factor A growth factor is a naturally occurring substance capable of stimulating cell proliferation Cell proliferation is the process by which ''a cell grows and divides to produce two daughter cells''. Cell proliferation leads to an exponential gro ...
*
Intracrine Intracrine refers to a hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavi ...
* List of investigational sex-hormonal agents *
Metabolomics Metabolomics is the scientific study of chemical processes involving metabolites, the small molecule substrates, intermediates and products of cell metabolism. Specifically, metabolomics is the "systematic study of the unique chemical fingerprint ...
*
Neuroendocrinology Neuroendocrinology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physi ...
*
Paracrine signalingParacrine signaling is form of cell signaling or cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. Signaling molecules known as paracrine factors diffuse over a rel ...
*
Plant hormone Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (biology), cells and coordinates multiple-cell actions. A sig ...
s, a.k.a. plant growth regulators *
Semiochemical A semiochemical, from the Greek wiktionary:σημεῖον, σημεῖον (''semeion''), meaning "signal", is a chemical substance or mixture released by an organism that affects the behaviors of other individuals. Semiochemical communication c ...
*
Sex-hormonal agent__NOTOC__ A sex-hormonal agent, also known as a sex-hormone receptor modulator, is a type of hormonal agent which specifically modulates the effects of sex hormones and of their biological targets, the sex hormone receptors. The sex hormones includ ...
*
Sexual motivation and hormonesSexual motivation is influenced by hormones such as testosterone, estrogen, progesterone, oxytocin, and vasopressin. In most mammalian species, sex hormones control the ability and motivation to engage in sexual behaviours. Measuring sexual motiva ...
*
XenohormoneXenohormones or environmental hormones are a group of compounds showing endocrine hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transport ...


References


External links


HMRbase: A database of hormones and their receptors
* {{Authority control * Physiology Endocrinology Cell signaling Signal transduction Human female endocrine system