Endocrinology

{{Main|Endocrine system}} Endocrinology is the study of the endocrine system in the human body.{{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}} This is a system of glands 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) 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.{{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}}{{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}}{{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}}

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 signals (a chemical that acts on the same cell), and intracrine signals (a chemical that acts within the same cell).{{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}} 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}}

Griffin and Ojeda identify three different classes of hormones based on their chemical composition:{{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 }}

{{multiple image

| footer = Examples of amine hormones

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| image1 = Norepinephrine structure with descriptor.svg

| caption1 = Norepinephrine

| image2 = Triiodothyronine.svg

| caption2 = Triiodothyronine

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Amines, such as norepinephrine, epinephrine, and dopamine (catecholamines), are derived from single amino acids, in this case tyrosine. Thyroid hormones such as 3,5,3'-triiodothyronine (T3) and 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.{{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 }}

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}}

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| image1 = Cortisol2.svg

| caption1 = Cortisol

| image2 = Cholecalciferol.svg

| caption2 = Vitamin D₃

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Steroid hormones are converted from their parent compound, cholesterol. Mammalian steroid hormones can be grouped into five groups by the receptors to which they bind: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestogens. 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.

{{Infobox Occupation

| name= Endocrinologist

| image=

| caption= manjoi

| official_names= Doctor, Medical specialist

| type= 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= Hospitals, Clinics

| related_occupation=

}}

Although every organ system secretes and responds to hormones (including the brain, lungs, heart, intestine, 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, adrenals, 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 list of diseases).

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.{{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}}

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 incidentalomas, which may or may not represent disease.{{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 }}

Endocrinology involves caring for the person as well as the disease. Most endocrine disorders are chronic diseases 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.

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, 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}}

• Diabetes mellitus: This is a chronic condition that affects how your body regulates 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.{{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}}
• 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 hormones that regulate your metabolism, heart rate, and body temperature. Common thyroid disorders include hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid).
• Adrenal disorders: The adrenal glands are located on top of your kidneys. They produce hormones that help regulate blood pressure, blood sugar, and the body's response to stress. Common adrenal disorders include Cushing syndrome (excess cortisol production) and Addison's disease (adrenal insufficiency).
• 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 disorders include acromegaly (excess growth hormone production) and Cushing's disease (excess ACTH production).
• Metabolic disorders: These are conditions that affect how your body processes food into energy. Common metabolic disorders include obesity, high cholesterol, and gout.
• Calcium and bone disorders: 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 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 cancers: These are cancers that develop in the endocrine glands. Endocrinologists can help diagnose and treat these cancers.

: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.

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.{{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}}{{Cite web |title=Homepage |url=https://www.thyroid.org/ |access-date=2024-08-02 |website=American Thyroid Association |language=en-US}}

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

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

The European Society for Paediatric Endocrinology{{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}} is the largest international professional association dedicated solely to paediatric endocrinology. There are numerous similar associations around the world.

File:Arnold Adolph Berthold.gif is known as a pioneer in endocrinology.]]

The earliest study of endocrinology began in China. The Chinese were isolating sex and pituitary hormones from human urine and using them for medicinal purposes by 200 BC.{{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}} They used many complex methods, such as sublimation of steroid hormones. 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.

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 Greek and Roman thinkers such as Aristotle, Hippocrates, Lucretius, Celsus, and Galen, according to Freeman et al.,{{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 }} and these theories held sway until the advent of germ theory, physiology, and organ basis of pathology in the 19th century.

In 1849, Arnold Berthold noted that castrated cockerels did not develop combs and wattles or exhibit overtly male behaviour.{{cite journal | author = Berthold AA | date = 1849 | title = Transplantation der Hoden | journal = Arch. Anat. Physiol. Wiss. Med. | volume = 16 | pages = 42–6 }} 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.{{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}}

Graves' disease was named after Irish doctor Robert James Graves,{{WhoNamedIt|doctor|695|Robert James Graves}} 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,{{WhoNamedIt|doctor|1471|Giuseppe Flajani}} and by the English physician Caleb Hillier Parry (a friend of Edward Jenner) in the late 18th century.{{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}} Thomas Addison was first to describe Addison's disease in 1849.{{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 }}

File:ThomasAddison.jpg]]

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.{{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}} 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.{{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 }}

Neurohormones were first identified by Otto Loewi in 1921.Loewi, O. Uebertragbarkeit der Herznervenwirkung. Pfluger's Arch. ges Physiol. 1921;189:239-42. 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 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 hormones. The first example of such work being done was in 1962 by 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 (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.{{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 }}

• Comparative endocrinology
• Endocrine disease
• Hormone
• Hormone replacement therapy
• Neuroendocrinology
• Pediatric endocrinology
• Reproductive endocrinology and infertility
• Wildlife endocrinology
• List of instruments used in endocrinology

{{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:Endocrine system

Category:Hormones