View source for Endocrinology

{{Short description|Branch of medicine pertaining to the endocrine system}}
{{For|the academic journal|Endocrinology (journal)}}
{{Infobox medical speciality
| title        = Endocrinology
| subdivisions =
| image        = [[File:Blausen 0345 EndocrineSystem Female2.png|225px]]
| caption      = Illustration depicting the primary endocrine organs of a female
| system       = [[Endocrine system|Endocrine]]
| diseases     = [[Diabetes]], [[Thyroid disease]], [[Androgen excess]]
| tests        = [[Thyroid function tests]], [[Blood sugar level]]s
| specialist   = [[Endocrinologist]]
| glossary     = [[Glossary of medicine]]
}}
'''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 [[secretion]]s known as [[hormone]]s. It is also concerned with the integration of developmental events proliferation, growth, and differentiation, and the psychological or behavioral activities of [[metabolism]], [[human development (biology)|growth and development]], [[tissue (biology)|tissue]] function, [[sleep]], [[digestion]], [[Respiration (physiology)|respiration]], [[excretion]], [[mood (psychology)|mood]], [[Stress (physiology)|stress]], [[lactation]], [[Motor coordination|movement]], [[reproduction]], and [[sensory perception]] caused by [[hormone]]s. Specializations include behavioral endocrinology and [[comparative endocrinology]].<ref>{{Cite journal |last1=Al-hussaniy |first1=Hany |last2=AL-Biati |first2=Haedar A |date=2022-10-12 |title=The Role of Leptin Hormone, Neuropeptide Y, Ghrelin and Leptin/Ghrelin ratio in Obesogenesis |url=http://pharmacoj.com/ojs/index.php/Medph/article/view/10 |journal=Medical and Pharmaceutical Journal |language=en |volume=1 |issue=2 |pages=12–23 |doi=10.55940/medphar20227 |issn=2957-6067|doi-access=free }}</ref>

The endocrine system consists of several [[glands]], all in different parts of the body, that secrete hormones directly into the blood rather than into a [[Duct (anatomy)|duct]] system. Therefore, [[endocrine gland]]s are regarded as ductless glands. Hormones have many different functions and modes of action; one hormone may have several effects on different target organs, and, conversely, one target organ may be affected by more than one hormone.

==The endocrine system==
{{Main|Endocrine system}} Endocrinology is the study of the endocrine system in the [[human body]].<ref>{{cite web | title = Endocrinology, Diabetes and Metabolism Specialty Description | publisher = American Medical Association | url = https://www.ama-assn.org/specialty/endocrinology-diabetes-and-metabolism-specialty-description | access-date = 14 September 2020}}</ref> This is a system of [[gland]]s which secrete hormones. Hormones are chemicals that affect the actions of different organ systems in the body. Examples include [[thyroid hormone]], [[growth hormone]], and [[insulin]]. The endocrine system involves a number of feedback mechanisms, so that often one hormone (such as [[Thyroid-stimulating hormone|thyroid stimulating hormone]]) will control the action or release of another secondary hormone (such as [[thyroid hormone]]). If there is too much of the secondary hormone, it may provide negative feedback to the primary hormone, maintaining [[homeostasis]].<ref>{{Citation |last=Carroll |first=Robert G. |title=13 - Endocrine System |date=2007-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780323043182500194 |work=Elsevier's Integrated Physiology |pages=157–176 |editor-last=Carroll |editor-first=Robert G. |access-date=2023-11-15 |place=Philadelphia |publisher=Mosby |isbn=978-0-323-04318-2}}</ref><ref>{{Cite journal |last1=Molnar |first1=Charles |last2=Gair |first2=Jane |date=2015-05-14 |title=11.4 Endocrine System |url=https://opentextbc.ca/biology/chapter/11-4-endocrine-system/ |language=en}}</ref><ref>{{Cite web |title=How the Pill Works {{!}} American Experience {{!}} PBS |url=https://www.pbs.org/wgbh/americanexperience/features/pill-how-pill-works/ |access-date=2023-11-15 |website=www.pbs.org |language=en}}</ref>

In the original 1902 definition by Bayliss and Starling (see below), they specified that, to be classified as a hormone, a chemical must be produced by an organ, be released (in small amounts) into the blood, and be transported by the blood to a distant organ to exert its specific function. This definition holds for most "classical" hormones, but there are also [[paracrine]] mechanisms (chemical communication between cells within a tissue or organ), [[autocrine signaling|autocrine]] signals (a chemical that acts on the same cell), and [[intracrine]] signals (a chemical that acts within the same cell).<ref>{{cite book |author=Nussey S|author2=Whitehead S |title=Endocrinology: An Integrated Approach  |date=2001 |isbn=978-1-85996-252-7 |publisher=Bios Scientific Publ. |location=Oxford}}</ref> A [[neuroendocrine]] signal is a "classical" hormone that is released into the blood by a neurosecretory neuron (see article on [[neuroendocrinology]]).{{cn|date=March 2024}}

=== Hormones ===
Griffin and Ojeda identify three different classes of hormones based on their chemical composition:<ref>{{cite book |author=Ojeda, Sergio R.|author2=Griffin, James Bennett |title=Textbook of endocrine physiology |url=https://archive.org/details/textbookofendocr00oxfo|url-access=registration|publisher=Oxford University Press |location=Oxford [Oxfordshire] |date=2000 |edition=4th |isbn=978-0-19-513541-1 }}</ref>

====Amines====
{{multiple image
| footer = Examples of '''amine hormones'''
| total_width = 270
| image1 = Norepinephrine structure with descriptor.svg
| caption1 = [[Norepinephrine]]
| image2 = Triiodothyronine.svg
| caption2 = [[Triiodothyronine]]
}}
Amines, such as [[norepinephrine]], [[epinephrine]], and [[dopamine]] ([[catecholamines]]), are derived from single [[amino acid]]s, in this case tyrosine. [[Thyroid]] hormones such as [[Triiodothyronine|3,5,3'-triiodothyronine]] (T3) and [[Levothyroxine|3,5,3',5'-tetraiodothyronine]] (thyroxine, T4) make up a subset of this class because they derive from the combination of two iodinated tyrosine amino acid residues.<ref>{{Cite journal |last1=Carvalho |first1=Denise P. |last2=Dupuy |first2=Corinne |date=2017-12-15 |title=Thyroid hormone biosynthesis and release |url=https://www.sciencedirect.com/science/article/pii/S0303720717300515 |journal=Molecular and Cellular Endocrinology |series=A century of thyroid hormone research - Vol. I: The expanded thyroid hormone network: novel metabolites and modes of action |volume=458 |pages=6–15 |doi=10.1016/j.mce.2017.01.038 |pmid=28153798 |s2cid=31150531 |issn=0303-7207|url-access=subscription }}</ref>

====Peptide and protein====
[[Peptide hormones]] and protein hormones consist of three (in the case of [[thyrotropin-releasing hormone]]) to more than 200 (in the case of [[follicle-stimulating hormone]]) amino acid residues and can have a molecular mass as large as 31,000 grams per mole. All hormones secreted by the pituitary gland are peptide hormones, as are [[leptin]] from adipocytes, [[ghrelin]] from the stomach, and [[insulin]] from the [[pancreas]].{{cn|date=May 2022}}

====Steroid====
{{multiple image
| footer = Examples of '''steroid hormones'''
| total_width = 270
| image1 = Cortisol2.svg
| caption1 = [[Cortisol]]
| image2 = Cholecalciferol.svg
| caption2 = [[Cholecalciferol|Vitamin D<sub>3</sub>]]
}}
[[Steroid hormones]] are converted from their parent compound, [[cholesterol]]. [[Mammal]]ian steroid hormones can be grouped into five groups by the receptors to which they bind: [[glucocorticoid]]s, [[mineralocorticoid]]s, [[androgen]]s, [[estrogen]]s, and [[progestogen]]s. Some forms of [[vitamin D]], such as [[calcitriol]], are steroid-like and bind to homologous receptors, but lack the characteristic fused ring structure of true steroids.

==As a profession==

{{Infobox Occupation
| name= Endocrinologist
| image=
| caption= manjoi
| official_names= Doctor, Medical specialist
<!------------Details------------------->
| type= [[Specialty (medicine)|Specialty]]
| activity_sector= [[Medicine]]
| competencies=
| formation= *[[Doctor of Medicine]] (M.D.)
* [[Doctor of Osteopathic Medicine]] (D.O.)
* [[Bachelor of Medicine, Bachelor of Surgery]] (M.B.B.S.)
| employment_field= [[Hospital]]s, [[Clinic]]s
| related_occupation=
}}

Although every organ system secretes and responds to hormones (including the [[Human brain|brain]], [[Human lungs|lungs]], [[Human heart|heart]], [[intestine]], [[human skin|skin]], and the [[kidneys]]), the clinical specialty of endocrinology focuses primarily on the ''endocrine organs'', meaning the organs whose primary function is hormone secretion.  These organs include the [[pituitary]], [[thyroid]], [[adrenal]]s, [[ovary|ovaries]], [[testes]], and  [[pancreas]].

An ''endocrinologist'' is a [[physician]] who specializes in treating disorders of the endocrine system, such as [[diabetes]], [[hyperthyroidism]], and many others (see [[Endocrine disease|list of diseases]]).

===Work===
The medical specialty of endocrinology involves the diagnostic evaluation of a wide variety of symptoms and variations and the long-term management of disorders of deficiency or excess of one or more hormones.<ref>{{Cite web |title=What Is an Endocrinologist? |url=https://www.aace.com/all-about-endocrinology/what-endocrinologist |access-date=2024-06-21 |website=American Association of Clinical Endocrinology |language=en}}</ref>

The diagnosis and treatment of endocrine diseases are guided by [[laboratory]] tests to a greater extent than for most specialties. Many diseases are investigated through ''excitation/stimulation'' or ''inhibition/suppression'' testing. This might involve injection with a stimulating agent to test the function of an endocrine organ. Blood is then sampled to assess the changes of the relevant hormones or metabolites. An endocrinologist needs extensive knowledge of [[clinical chemistry]] and [[biochemistry]] to understand the uses and limitations of the investigations.

A second important aspect of the practice of endocrinology is distinguishing human variation from disease. Atypical patterns of physical development and abnormal test results must be assessed as indicative of disease or not. [[Diagnostic imaging]] of endocrine organs may reveal incidental findings called [[incidentaloma]]s, which may or may not represent disease.<ref>{{Cite journal |last1=Grumbach |first1=Melvin M. |last2=Biller |first2=Beverly M. K. |last3=Braunstein |first3=Glenn D. |last4=Campbell |first4=Karen K. |last5=Carney |first5=J. Aidan |last6=Godley |first6=Paul A. |last7=Harris |first7=Emily L. |last8=Lee |first8=Joseph K. T. |last9=Oertel |first9=Yolanda C. |last10=Posner |first10=Mitchell C. |last11=Schlechte |first11=Janet A. |last12=Wieand |first12=H. Samuel |date=2003-03-04 |title=Management of the clinically inapparent adrenal mass ("incidentaloma") |url=https://pubmed.ncbi.nlm.nih.gov/12614096/ |journal=Annals of Internal Medicine |volume=138 |issue=5 |pages=424–429 |doi=10.7326/0003-4819-138-5-200303040-00013 |issn=1539-3704 |pmid=12614096|s2cid=23454526 }}</ref>

Endocrinology involves caring for the person as well as the disease. Most endocrine disorders are [[chronic disease]]s that need lifelong care. Some of the most common endocrine diseases include [[diabetes]] mellitus, [[hypothyroidism]] and the [[metabolic syndrome]]. Care of diabetes, obesity and other chronic diseases necessitates understanding the patient at the personal and social level as well as the molecular, and the physician–patient relationship can be an important therapeutic process.

Apart from treating patients, many endocrinologists are involved in [[clinical science]] and [[medical research]], [[teaching]], and [[hospital management]].

===Training===
Endocrinologists are specialists of [[internal medicine]] or [[pediatrics]]. Reproductive endocrinologists deal primarily with problems of [[fertility]] and menstrual function—often training first in obstetrics. Most qualify as an [[internist]], [[pediatrician]], or [[gynecologist]] for a few years before specializing, depending on the local training system. In the U.S. and Canada, training for board certification in internal medicine, [[pediatrics]], or [[gynecology]] after medical school is called residency. Further formal training to subspecialize in adult, [[pediatric endocrinology|pediatric]], or reproductive endocrinology is called a fellowship. Typical training for a North American endocrinologist involves 4 years of college, 4 years of medical school, 3 years of residency, and 2 years of fellowship. In the US, adult endocrinologists are board certified by the [[American Board of Internal Medicine]] (ABIM) or the [[American Osteopathic Board of Internal Medicine]] (AOBIM) in Endocrinology, Diabetes and Metabolism.{{cn|date=May 2022}}

== Diseases treated by endocrinologists ==

* '''[[Diabetes management|Diabetes]] mellitus:''' This is a chronic condition that affects how your body regulates [[Blood sugar level|blood sugar]]. There are two main types: [[type 1 diabetes]], which is an autoimmune disease that occurs when the body attacks the cells that produce insulin, and [[type 2 diabetes]], which is a condition in which the body either doesn't produce enough insulin or doesn't use it effectively.<ref>{{Cite web |last=CDC |date=2024-07-19 |title=Diabetes Basics |url=https://www.cdc.gov/diabetes/about/index.html#:~:text=Diabetes%20is%20a%20chronic%20(long,diabetes%20(diabetes%20while%20pregnant). |access-date=2025-03-28 |website=Diabetes |language=en-us}}</ref>
* '''[[Thyroid disease|Thyroid disorders]]:''' These are conditions that affect the thyroid gland, a butterfly-shaped gland located in the front of your neck. The thyroid gland produces [[Hormone|hormones]] that regulate your metabolism, heart rate, and [[Thermoregulation|body temperature]]. Common thyroid disorders include hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid).
* '''[[Adrenal gland disorder|Adrenal disorders]]:''' The adrenal glands are located on top of your [[Kidney|kidneys]]. They produce hormones that help regulate blood pressure, blood sugar, and the body's response to stress. Common [[Adrenal gland disorder|adrenal disorders]] include Cushing syndrome (excess cortisol production) and Addison's disease (adrenal insufficiency).
* '''[[Pituitary disease|Pituitary disorders]]:''' The pituitary gland is a pea-sized gland located at the base of the brain. It produces hormones that control many other hormone-producing glands in the body. Common [[Pituitary disease|pituitary disorders]] include acromegaly (excess growth hormone production) and Cushing's disease (excess ACTH production).
* '''[[Metabolic disorder|Metabolic disorders]]:''' These are conditions that affect how your body processes food into energy. Common [[Metabolism|metabolic]] disorders include obesity, high [[cholesterol]], and gout.
* '''[[Calcium]] and bone disorders:'''  [[Endocrinologist (magazine)|Endocrinologists]] also treat conditions that affect calcium levels in the blood, such as hyperparathyroidism (too much parathyroid hormone) and osteoporosis (weak bones).
* '''Sexual and [[Reproductive disorder|reproductive disorders]]:''' Endocrinologists can also help diagnose and treat hormonal problems that affect [[sexual development]] and function, such as polycystic ovary syndrome (PCOS) and erectile dysfunction.
* '''[[Endocrine surgery|Endocrine]] cancers:''' These are cancers that develop in the endocrine glands.  Endocrinologists can help diagnose and treat these [[Cancer|cancers]].

== Diseases and medicine ==

===Diseases===
:See main article at ''[[Endocrine diseases]]''
Endocrinology also involves the study of the diseases of the endocrine system. These diseases may relate to too little or too much secretion of a hormone, too little or too much action of a hormone, or problems with receiving the hormone.

=== Societies and Organizations ===
Because endocrinology encompasses so many conditions and diseases, there are many organizations that provide education to patients and the public. [[The Hormone Foundation]] is the public education affiliate of [[The Endocrine Society]] and provides information on all endocrine-related conditions.  Other educational organizations that focus on one or more endocrine-related conditions include the [[American Diabetes Association]], [[Human Growth Foundation]], American Menopause Foundation, Inc., and American Thyroid Association.<ref>{{Cite web |title=North American Menopause Society (NAMS) - Focused on Providing Physicians, Practitioners & Women Menopause Information, Help & Treatment Insights |url=https://www.menopause.org/ |access-date=2024-08-02 |website=www.menopause.org}}</ref><ref>{{Cite web |title=Homepage |url=https://www.thyroid.org/ |access-date=2024-08-02 |website=American Thyroid Association |language=en-US}}</ref>

In North America the principal professional organizations of endocrinologists include The Endocrine Society,<ref>{{cite web|url=http://www.endo-society.org|title=Home - Endocrine Society|website=www.endo-society.org}}</ref> the [[American Association of Clinical Endocrinologists (AACE)|American Association of Clinical Endocrinologists]],<ref>{{cite web| url = http://www.aace.com| title = American Association of Clinical Endocrinologists}}</ref> the American Diabetes Association,<ref>{{cite web|url=http://www.diabetes.org|title=American Diabetes Association|website=American Diabetes Association}}</ref> the Lawson Wilkins Pediatric Endocrine Society,<ref>{{cite web|url=http://www.lwpes.org|title=Pediatric Endocrine Society|website=www.lwpes.org}}</ref> and the American Thyroid Association.<ref>{{cite web|url=http://www.thyroid.org|title=American Thyroid Association - ATA|website=www.thyroid.org}}</ref>

In Europe, the European Society of Endocrinology (ESE) and the European Society for Paediatric Endocrinology (ESPE) are the main organisations representing professionals in the fields of adult and paediatric endocrinology, respectively.

In the United Kingdom, the [[Society for Endocrinology]]<ref>{{cite web|url=http://www.endocrinology.org|title=Society for Endocrinology - A world-leading authority on hormones|website=www.endocrinology.org}}</ref> and the British Society for Paediatric Endocrinology and Diabetes<ref>{{cite web|url=http://www.bsped.org.uk|title=BSPED - Home|website=www.bsped.org.uk}}</ref> are the main professional organisations.

The European Society for Paediatric Endocrinology<ref>{{cite web|url=http://www.eurospe.org|title=ESPE - European Society of Paediatric Endocrinology - Improving the clinical care of children and adolescents with endocrine conditions|website=www.eurospe.org}}</ref> is the largest international professional association dedicated solely to paediatric endocrinology. There are numerous similar associations around the world.

== History ==
[[File:Arnold Adolph Berthold.gif|thumb|150px|[[Arnold Adolph Berthold|Arnold Berthold]] is known as a pioneer in endocrinology.]]
The earliest study of endocrinology began in China.<ref name="genius" /> The Chinese were isolating sex and pituitary hormones from human [[urine]] and using them for medicinal purposes by 200 BC.<ref name="genius">{{cite book|last=Temple|first=Robert|title=The genius of China: 3,000 years of science, discovery & invention|date=2007|orig-year=1986|publisher=Andre Deutsch|location=London|isbn=978-0-233-00202-6|pages=141–145|edition=3rd}}</ref> They used many complex methods, such as sublimation of steroid hormones.<ref name="genius" /> Another method specified by Chinese texts—the earliest dating to 1110—specified the use of [[saponin]] (from the beans of ''[[Gleditsia sinensis]]'') to extract hormones, but [[gypsum]] (containing [[calcium sulfate]]) was also known to have been used.<ref name="genius" />

Although most of the relevant tissues and endocrine glands had been identified by early anatomists, a more humoral approach to understanding biological function and disease was favoured by the [[Ancient Greece|ancient Greek]] and [[Ancient Rome|Roman]] thinkers such as [[Aristotle]], [[Hippocrates]], [[Lucretius]], [[Aulus Cornelius Celsus|Celsus]], and [[Galen]], according to Freeman et al.,<ref>{{cite journal |author=Freeman ER|author2=Bloom DA|author3=McGuire EJ |title=A brief history of testosterone |journal=Journal of Urology |volume=165 |issue=2 |pages=371–3 |date=2001 |pmid=11176375 |doi=10.1097/00005392-200102000-00004 }}</ref> and these theories held sway until the advent of [[germ theory of disease|germ theory]], physiology, and organ basis of pathology in the 19th century.

In 1849, [[Arnold Adolph Berthold|Arnold Berthold]] noted that castrated cockerels did not develop combs and wattles or exhibit overtly male behaviour.<ref>{{cite journal | author = Berthold AA | date = 1849 | title = Transplantation der Hoden | journal = Arch. Anat. Physiol. Wiss. Med. | volume = 16 | pages = 42–6 }}</ref> He found that replacement of testes back into the abdominal cavity of the same bird or another castrated bird resulted in normal behavioural and morphological development, and he concluded (erroneously) that the testes secreted a substance that "conditioned" the blood that, in turn, acted on the body of the cockerel. In fact, one of two other things could have been true: that the testes modified or activated a constituent of the blood or that the testes removed an inhibitory factor from the blood. It was not proven that the testes released a substance that engenders male characteristics until it was shown that the extract of testes could replace their function in castrated animals. Pure, crystalline [[testosterone]] was isolated in 1935.<ref>{{cite journal | author = David K| author2 = Dingemanse E| author3 = Freud J| date = 1935 | title = Uber krystallinisches mannliches Hormon aus Hoden (Testosteron) wirksamer als aus harn oder aus Cholesterin bereitetes Androsteron | journal = Hoppe-Seyler's Z Physiol Chem | volume = 233 | issue = 5–6| pages = 281–283 | doi = 10.1515/bchm2.1935.233.5-6.281 |display-authors=etal}}</ref>

[[Graves' disease]] was named after Irish doctor [[Robert James Graves]],<ref>{{WhoNamedIt|doctor|695|Robert James Graves}}</ref> who described a case of [[goiter]] with [[exophthalmos]] in 1835. The German [[Karl Adolph von Basedow]] also independently reported the same constellation of symptoms in 1840, while earlier reports of the disease were also published by the Italians Giuseppe Flajani and Antonio Giuseppe Testa, in 1802 and 1810 respectively,<ref>{{WhoNamedIt|doctor|1471|Giuseppe Flajani}}</ref> and by the English physician [[Caleb Hillier Parry]] (a friend of [[Edward Jenner]]) in the late 18th century.<ref>{{cite journal |author=Hull G |title=Caleb Hillier Parry 1755–1822: a notable provincial physician |journal=Journal of the Royal Society of Medicine |volume=91 |issue=6 |pages=335–8 |date=1998 |pmid=9771526 |pmc=1296785 |doi=10.1177/014107689809100618}}</ref> [[Thomas Addison]] was first to describe [[Addison's disease]] in 1849.<ref>{{cite journal |author=Ten S|author2= New M|author3=Maclaren N |title=Clinical review 130: Addison's disease 2001 |journal=Journal of Clinical Endocrinology & Metabolism |volume=86 |issue=7 |pages=2909–22 |date=2001 |doi= 10.1210/jcem.86.7.7636|pmid=11443143 |url=http://jcem.endojournals.org/cgi/content/full/86/7/2909 |doi-access=free |url-access=subscription }}</ref>
[[File:ThomasAddison.jpg|thumb|150px|[[Thomas Addison]]]]
In 1902 [[William Bayliss]] and [[Ernest Starling]] performed an experiment in which they observed that acid instilled into the [[duodenum]] caused the [[pancreas]] to begin secretion, even after they had removed all nervous connections between the two.<ref>{{cite journal | last1=Bayliss | first1=W. M. | last2=Starling | first2=E. H. | title=The mechanism of pancreatic secretion | journal=The Journal of Physiology | publisher=Wiley | volume=28 | issue=5 | date=1902-09-12 | issn=0022-3751 | pmid=16992627|  pmc=1540572| doi=10.1113/jphysiol.1902.sp000920 | pages=325–353}}</ref> The same response could be produced by injecting extract of jejunum mucosa into the jugular vein, showing that some factor in the mucosa was responsible. They named this substance "[[secretin]]" and coined the term ''hormone'' for chemicals that act in this way.

[[Joseph von Mering]] and [[Oskar Minkowski]] made the observation in 1889 that removing the [[pancreas]] surgically led to an increase in [[blood sugar]], followed by a coma and eventual death—symptoms of [[diabetes mellitus]]. In 1922, Banting and Best realized that homogenizing the pancreas and injecting the derived extract reversed this condition.<ref>{{cite journal |author=Bliss M |title=J. J. R. Macleod and the discovery of insulin |journal=Quarterly Journal of Experimental Physiology |volume=74 |issue=2 |pages=87–96 |date=1989 |pmid=2657840 |doi=10.1113/expphysiol.1989.sp003266 |doi-access=free }}</ref>

[[Neurohormone]]s were first identified by [[Otto Loewi]] in 1921.<ref>Loewi, O. ''Uebertragbarkeit der Herznervenwirkung.'' Pfluger's Arch. ges Physiol. 1921;189:239-42.</ref>  He incubated a frog's heart (innervated with its [[vagus nerve]] attached) in a saline bath, and left in the solution for some time. The solution was then used to bathe a non-innervated second heart. If the vagus nerve on the first heart was stimulated, negative [[inotropic]] (beat amplitude) and [[chronotropic]] (beat rate) activity were seen in both hearts. This did not occur in either heart if the vagus nerve was not stimulated. The vagus nerve was adding something to the saline solution. The effect could be blocked using [[atropine]], a known [[Enzyme inhibitor|inhibitor]] to [[heart]] vagal nerve stimulation. Clearly, something was being secreted by the [[vagus nerve]] and affecting the heart. The "vagusstuff" (as Loewi called it) causing the myotropic (muscle enhancing) effects was later identified to be [[acetylcholine]] and [[norepinephrine]]. Loewi won the Nobel Prize for his discovery.

Recent work in endocrinology focuses on the molecular mechanisms responsible for triggering the effects of [[hormone]]s. The first example of such work being done was in 1962 by [[Earl Wilbur Sutherland Jr.|Earl Sutherland]]. Sutherland investigated whether hormones enter cells to evoke action, or stayed outside of cells. He studied [[norepinephrine]], which acts on the liver to convert [[glycogen]] into [[glucose]] via the activation of the [[phosphorylase]] enzyme. He homogenized the liver into a membrane fraction and soluble fraction (phosphorylase is soluble), added norepinephrine to the membrane fraction, extracted its soluble products, and added them to the first soluble fraction. Phosphorylase activated, indicating that norepinephrine's target receptor was on the cell membrane, not located intracellularly. He later identified the compound as cyclic AMP ([[Cyclic adenosine monophosphate|cAMP]]) and with his discovery created the concept of second-messenger-mediated pathways. He, like Loewi, won the Nobel Prize for his groundbreaking work in endocrinology.<ref>{{cite journal |author=Sutherland EW |title=Studies on the mechanism of hormone action |journal=Science |volume=177 |issue=4047 |pages=401–8 |date=1972 |pmid=4339614 |doi= 10.1126/science.177.4047.401|bibcode = 1972Sci...177..401S }}</ref>

==See also==
* [[Comparative endocrinology]]
* [[Endocrine disease]]
* [[Hormone]]
* [[Hormone replacement therapy]]
* [[Neuroendocrinology]]
* [[Pediatric endocrinology]]
* [[Reproductive endocrinology and infertility]]
* [[Wildlife endocrinology]]
* [[List of instruments used in endocrinology]]

== References ==
{{Reflist}}

{{Clear}}
{{Medicine}}
{{endocrine system}}
{{Endocrinology}}
{{Endocrine system procedures}}
{{Disease of the pancreas and glucose metabolism}}
{{Lipid metabolism disorders}}
{{Hypothalamic disease}}
{{Pituitary disease}}
{{Thyroid disease}}
{{Parathyroid disease}}
{{Adrenal gland disorder}}
{{Gonadal disorder}}
{{Growth disorder}}
{{Disorders involving multiple endocrine glands}}
{{Nutritional pathology}}
{{Authority control}}

[[Category:Endocrinology| ]]
[[Category:Endocrine system]]
[[Category:Hormones]]