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89-447: 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 system. Therefore, endocrine glands 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. Endocrinology

178-415: A peptide hormone , calcitonin . The thyroid hormones influence the metabolic rate and protein synthesis and growth and development in children. Calcitonin plays a role in calcium homeostasis . Secretion of the two thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is secreted from the anterior pituitary gland. TSH is regulated by thyrotropin-releasing hormone (TRH), which

267-555: A bilobed diverticulum through the thyroglossal duct . Over the next few weeks, it migrates to the base of the neck, passing in front of the hyoid bone. During migration, the thyroid remains connected to the tongue by a narrow canal, the thyroglossal duct. At the end of the fifth week the thyroglossal duct degenerates, and over the following two weeks the detached thyroid migrates to its final position. The fetal hypothalamus and pituitary start to secrete thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH). TSH

356-417: A different method of secretion. Endocrine glands are ductless and secrete their products, hormones , directly into interstitial spaces to be taken up into the bloodstream. Exocrine glands secrete their products through a duct into a body cavity or outer surface. Glands are mostly composed of epithelial tissue , and typically have a supporting framework of connective tissue, and a capsule. Every gland

445-503: 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

534-472: A gland. The diseased gland has abnormal formation or development of glandular tissue which is sometimes tumorous . Thyroid The thyroid , or thyroid gland , is an endocrine gland in vertebrates . In humans, it is a butterfly-shaped gland located in the neck below the Adam's apple . It consists of two connected lobes . The lower two thirds of the lobes are connected by a thin band of tissue called

623-429: 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

712-443: 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

801-484: 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

890-611: A less modified type of epithelial cell. Glands are classified according to their shape. Glands are divided based on their function into two groups: Endocrine glands secrete substances that circulate through the bloodstream. The glands secrete their products through basal lamina into the bloodstream. Basal lamina typically can be seen as a layer around the glands to which more than a million tiny blood vessels are attached. These glands often secrete hormones which play an important role in maintaining homeostasis . The pineal gland , thymus gland , pituitary gland , thyroid gland , and

979-476: A narrow tissue band, called an "isthmus". It weighs 25 grams in adults, with each lobe being about 5 cm long, 3 cm wide, and 2 cm thick and the isthmus about 1.25 cm in height and width. The gland is usually larger in women than in men, and increases in size during pregnancy. The thyroid is near the front of the neck, lying against and around the front of the larynx and trachea . The thyroid cartilage and cricoid cartilage lie just above

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1068-454: A nodule is present, thyroid function tests determine whether the nodule is secreting excess thyroid hormones, causing hyperthyroidism. When the thyroid function tests are normal, an ultrasound is often used to investigate the nodule, and provide information such as whether the nodule is fluid-filled or a solid mass, and whether the appearance is suggestive of a benign or malignant cancer. A needle aspiration biopsy may then be performed, and

1157-449: A painless mass in the neck. Thyroid cancers are most often carcinomas , although cancer can occur in any tissue that the thyroid consists of, including cancer of C-cells and lymphomas. Cancers from other sites also rarely lodge in the thyroid. Radiation of the head and neck presents a risk factor for thyroid cancer, and cancer is more common in women than men, occurring at a rate of about 2:1. In most cases, thyroid cancer presents as

1246-484: A painless mass in the neck. It is very unusual for thyroid cancers to present with other symptoms, although in some cases cancer may cause hyperthyroidism. Most thyroid cancers are papillary , followed by follicular , medullary , and thyroid lymphoma . Because of the prominence of the thyroid gland, cancer is often detected earlier in the course of disease as the cause of a nodule, which may undergo fine-needle aspiration . Thyroid function tests will help reveal whether

1335-430: A return to normal function. The course of the illness takes place over several months, and is characterised by a painless goitre. Antibodies against thyroid peroxidase can be found on testing. The inflammation usually resolves without treatment, although thyroid hormone replacement may be needed during the period of hypothyroidism. The most common tumor affecting the thyroid is a benign adenoma , usually presenting as

1424-460: 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 ,

1513-445: A spherical arrangement of follicular cells . The follicular lumen is filled with colloid , a concentrated solution of thyroglobulin and is the site of synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Scattered among follicular cells and in spaces between the spherical follicles are another type of thyroid cell, parafollicular cells. These cells secrete calcitonin and so are also called C cells. In

1602-483: A subset of this class because they derive from the combination of two iodinated tyrosine amino acid residues. 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

1691-403: A very large structure is finally formed by repeated growth and sub-division. As a rule, the branches do not unite with one another. One exception to this rule is the liver ; this occurs when a reticulated compound gland is produced. In compound glands the more typical or secretory epithelium is found forming the terminal portion of each branch, and the uniting portions form ducts and are lined with

1780-487: A wide range of effects on the human body. These include: After secretion, only a very small proportion of the thyroid hormones travel freely in the blood. Most are bound to thyroxine-binding globulin (about 70%), transthyretin (10%), and albumin (15%). Only the 0.03% of T 4 and 0.3% of T 3 traveling freely have hormonal activity. In addition, up to 85% of the T 3 in blood is produced following conversion from T 4 by iodothyronine deiodinases in organs around

1869-460: 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. The diagnosis and treatment of endocrine diseases are guided by laboratory tests to

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1958-423: Is a protein within the colloid in the follicular lumen that is originally created within the rough endoplasmic reticulum of follicular cells and then transported into the follicular lumen. Thyroglobulin contains 123 units of tyrosine , which reacts with iodine within the follicular lumen. Iodine is essential for the production of the thyroid hormones. Iodine (I ) travels in the blood as iodide (I ), which

2047-489: Is a "classical" hormone that is released into the blood by a neurosecretory neuron (see article on neuroendocrinology ). Griffin and Ojeda identify three different classes of hormones based on their chemical composition: 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

2136-402: Is an autoimmune disorder in which the thyroid gland is infiltrated by the lymphocytes B cell and T cells . These progressively destroy the thyroid gland. In this way, Hasimoto's thyroiditis may have occurred insidiously, and only be noticed when thyroid hormone production decreases, causing symptoms of hypothyroidism. Hashimoto's is more common in females than males, much more common after

2225-423: Is an autoimmune disorder that is the most common cause of hyperthyroidism. In Graves' disease, for an unknown reason autoantibodies develop against the thyroid stimulating hormone receptor. These antibodies activate the receptor, leading to development of a goitre and symptoms of hyperthyroidism, such as heat intolerance, weight loss, diarrhoea and palpitations. Occasionally such antibodies block but do not activate

2314-617: Is essential for healthy neurodevelopment. The neuroendocrine parafollicular cells , also known as C cells, responsible for the production of calcitonin , are derived from foregut endoderm. This part of the thyroid then first forms as the ultimopharyngeal body , which begins in the ventral fourth pharyngeal pouch and joins the primordial thyroid gland during its descent to its final location. Aberrations in prenatal development can result in various forms of thyroid dysgenesis which can cause congenital hypothyroidism , and if untreated this can lead to cretinism . The primary function of

2403-486: Is first measurable at 11 weeks. By 18–20 weeks, the production of thyroxine (T 4 ) reaches a clinically significant and self-sufficient level. Fetal triiodothyronine (T 3 ) remains low, less than 15 ng/dL until 30 weeks, and increases to 50 ng/dL at full-term . The fetus needs to be self-sufficient in thyroid hormones in order to guard against neurodevelopmental disorders that would arise from maternal hypothyroidism . The presence of sufficient iodine

2492-423: Is formed by an ingrowth from an epithelial surface. This ingrowth may in the beginning possess a tubular structure, but in other instances glands may start as a solid column of cells which subsequently becomes tubulated. As growth proceeds, the column of cells may split or give off offshoots, in which case a compound gland is formed. In many glands, the number of branches is limited, in others (salivary, pancreas)

2581-401: Is managed with replacement of the thyroid hormones . This is usually given daily as an oral supplement, and may take a few weeks to become effective. Some causes of hypothyroidism, such as Postpartum thyroiditis and Subacute thyroiditis may be transient and pass over time, and other causes such as iodine deficiency may be able to be rectified with dietary supplementation. Graves' disease

2670-438: Is produced by the hypothalamus . Thyroid disorders include hyperthyroidism , hypothyroidism , thyroid inflammation ( thyroiditis ), thyroid enlargement ( goitre ), thyroid nodules , and thyroid cancer . Hyperthyroidism is characterized by excessive secretion of thyroid hormones: the most common cause is the autoimmune disorder Graves' disease . Hypothyroidism is characterized by a deficient secretion of thyroid hormones:

2759-461: Is secreted at an increased rate in situations such as cold exposure in order to stimulate thermogenesis . In addition to being suppressed by the presence of thyroid hormones, TSH production is blunted by dopamine , somatostatin , and glucocorticoids . The thyroid gland also produces the hormone calcitonin , which helps regulate blood calcium levels. Parafollicular cells produce calcitonin in response to high blood calcium . Calcitonin decreases

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2848-428: Is selectively taken up by thyroid cells, which over time destroys them. The chosen first-line treatment will depend on the individual and on the country where being treated. Surgery to remove the thyroid can sometimes be performed as a transoral thyroidectomy , a minimally invasive procedure . Surgery does however carry a risk of damage to the parathyroid glands and the recurrent laryngeal nerve , which innervates

2937-424: 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

3026-509: Is supplied with arterial blood from the superior thyroid artery , a branch of the external carotid artery , and the inferior thyroid artery , a branch of the thyrocervical trunk , and sometimes by an anatomical variant the thyroid ima artery , which has a variable origin. The superior thyroid artery splits into anterior and posterior branches supplying the thyroid, and the inferior thyroid artery splits into superior and inferior branches. The superior and inferior thyroid arteries join behind

3115-424: Is taken up into the follicular cells by a sodium-iodide symporter . This is an ion channel on the cell membrane which in the same action transports two sodium ions and an iodide ion into the cell. Iodide then travels from within the cell into the lumen, through the action of pendrin , an iodide-chloride antiporter . In the follicular lumen, the iodide is then oxidized to iodine. This makes it more reactive, and

3204-534: Is the largest international professional association dedicated solely to paediatric endocrinology. There are numerous similar associations around the world. 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. They used many complex methods, such as sublimation of steroid hormones. Another method specified by Chinese texts—the earliest dating to 1110—specified

3293-408: Is the study of the endocrine system in the human body . 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

3382-404: Is treated with anti-thyroid drugs such as propylthiouracil, which decrease the production of thyroid hormones, but hold a high rate of relapse. If there is no involvement of the eyes, then use of radioactive isotopes to ablate the gland may be considered. Surgical removal of the gland with subsequent thyroid hormone replacement may be considered, however this will not control symptoms associated with

3471-797: The American Diabetes Association , Human Growth Foundation , American Menopause Foundation, Inc., and American Thyroid Association. In North America the principal professional organizations of endocrinologists include The Endocrine Society, the American Association of Clinical Endocrinologists , the American Diabetes Association, the Lawson Wilkins Pediatric Endocrine Society, and the American Thyroid Association. In Europe,

3560-425: The anterior pituitary gland. TSH release in turn is stimulated by thyrotropin releasing hormone (TRH), released in a pulsatile manner from the hypothalamus . The thyroid hormones provide negative feedback to the thyrotropes TSH and TRH: when the thyroid hormones are high, TSH production is suppressed. This negative feedback also occurs when levels of TSH are high, causing TRH production to be suppressed. TRH

3649-420: The development of the embryo , at 3–4 weeks gestational age , the thyroid gland appears as an epithelial proliferation in the floor of the pharynx at the base of the tongue between the tuberculum impar and the copula linguae . The copula soon becomes covered over by the hypopharyngeal eminence at a point later indicated by the foramen cecum . The thyroid then descends in front of the pharyngeal gut as

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3738-422: The isthmus ( pl. : isthmi ). Microscopically, the functional unit of the thyroid gland is the spherical thyroid follicle , lined with follicular cells (thyrocytes), and occasional parafollicular cells that surround a lumen containing colloid . The thyroid gland secretes three hormones: the two thyroid hormones  – triiodothyronine (T 3 ) and thyroxine (T 4 )  – and

3827-411: The pancreas to begin secretion, even after they had removed all nervous connections between the two. 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

3916-405: The prelaryngeal lymph nodes (located just above the isthmus) and the pretracheal and paratracheal lymph nodes . The gland receives sympathetic nerve supply from the superior, middle and inferior cervical ganglion of the sympathetic trunk . The gland receives parasympathetic nerve supply from the superior laryngeal nerve and the recurrent laryngeal nerve . There are many variants in

4005-441: The vocal cords . If the entire thyroid gland is removed, hypothyroidism will inevitably result, and thyroid hormone substitutes will be needed. An underactive thyroid gland results in hypothyroidism . Typical symptoms are abnormal weight gain, tiredness, constipation , heavy menstrual bleeding , hair loss, cold intolerance, and a slow heart rate . Iodine deficiency is the most common cause of hypothyroidism worldwide, and

4094-664: 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 and the British Society for Paediatric Endocrinology and Diabetes are the main professional organisations. The European Society for Paediatric Endocrinology

4183-525: The Italians Giuseppe Flajani and Antonio Giuseppe Testa, in 1802 and 1810 respectively, and by the English physician Caleb Hillier Parry (a friend of Edward Jenner ) in the late 18th century. Thomas Addison was first to describe Addison's disease in 1849. In 1902 William Bayliss and Ernest Starling performed an experiment in which they observed that acid instilled into the duodenum caused

4272-407: The Nobel Prize for his groundbreaking work in endocrinology. Glands A gland is a cell or an organ in an animal's body that produces and secretes different substances that the organism needs, either into the bloodstream or into a body cavity or outer surface. A gland may also function to remove unwanted substances such as urine from the body. There are two types of gland each with

4361-625: 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. 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

4450-410: 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 . 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

4539-427: 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. 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

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4628-414: The age of 60, and has known genetic risk factors. Also more common in individuals with Hashimoto's thyroiditis are Type 1 diabetes , pernicious anaemia , Addison's disease vitiligo . Postpartum thyroiditis occurs sometimes following childbirth . After delivery, the thyroid becomes inflamed and the condition initially presents with a period of hyperthyroidism followed by hypothyroidism and, usually,

4717-429: The autoimmune disease Hashimoto's thyroiditis is the most common cause in the developed world. Other causes include congenital abnormalities, diseases causing transient inflammation, surgical removal or radioablation of the thyroid, the drugs amiodarone and lithium , amyloidosis , and sarcoidosis . Some forms of hypothyroidism can result in myxedema and severe cases can result in myxedema coma . Hypothyroidism

4806-618: The back of the thyroid lobes, usually close to the recurrent laryngeal nerve and the inferior thyroid artery, is called Zuckerkandl's tubercle . Other variants include a levator muscle of thyroid gland , connecting the isthmus to the body of the hyoid bone , and the presence of the small thyroid ima artery . At the microscopic level , there are three primary features of the thyroid— thyroid follicles , thyroid follicular cells , and parafollicular cells , first discovered by Geoffery Websterson in 1664. Thyroid follicles are small spherical groupings of cells 0.02–0.9mm in diameter that play

4895-410: 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). A neuroendocrine signal

4984-430: The blood. The hormones secreted from the gland are about 80–90% T 4 and about 10–20% T 3 . Deiodinase enzymes in peripheral tissues remove the iodine from MIT and DIT and convert T 4 to T 3 and RT 3. This is a major source of both RT 3 (95%) and T 3 (87%) in peripheral tissues. The production of thyroxine and triiodothyronine is primarily regulated by thyroid-stimulating hormone (TSH), released by

5073-572: The body. Thyroid hormones act by crossing the cell membrane and binding to intracellular nuclear thyroid hormone receptors TR-α 1 , TR-α 2 , TR-β 1 , and TR-β 2 , which bind with hormone response elements and transcription factors to modulate DNA transcription . In addition to these actions on DNA, the thyroid hormones also act within the cell membrane or within cytoplasm via reactions with enzymes , including calcium ATPase , adenylyl cyclase , and glucose transporters . The thyroid hormones are created from thyroglobulin . This

5162-475: The characteristic fused ring structure of true steroids. 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

5251-426: 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

5340-430: The extract of testes could replace their function in castrated animals. Pure, crystalline testosterone was isolated in 1935. Graves' disease was named after Irish doctor 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

5429-574: The eye or skin. Thyroid nodules are often found on the gland, with a prevalence of 4–7%. The majority of nodules do not cause any symptoms, thyroid hormone secretion is normal, and they are non-cancerous. Non-cancerous cases include simple cysts , colloid nodules , and thyroid adenomas . Malignant nodules, which only occur in about 5% of nodules, include follicular , papillary , medullary carcinomas and metastasis from other sites Nodules are more likely in females, those who are exposed to radiation, and in those who are iodine deficient. When

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5518-456: The gland and forms the septa that divide the thyroid tissue into microscopic lobules. The outer layer is continuous with the pretracheal fascia , attaching the gland to the cricoid and thyroid cartilages via a thickening of the fascia to form the posterior suspensory ligament of thyroid gland , also known as Berry's ligament. This causes the thyroid to move up and down with the movement of these cartilages when swallowing occurs. The thyroid

5607-475: The gland, below the Adam's apple . The isthmus extends from the second to third rings of the trachea , with the uppermost part of the lobes extending to the thyroid cartilage and the lowermost around the fourth to sixth tracheal rings. The infrahyoid muscles lie in front of the gland and the sternocleidomastoid muscle to the side. Behind the outer wings of the thyroid lie the two carotid arteries . The trachea, larynx, lower pharynx and esophagus all lie behind

5696-523: The iodine is attached to the active tyrosine units in thyroglobulin by the enzyme thyroid peroxidase . This forms the precursors of thyroid hormones monoiodotyrosine (MIT), and diiodotyrosine (DIT). When the follicular cells are stimulated by thyroid-stimulating hormone , the follicular cells reabsorb thyroglobulin from the follicular lumen. The iodinated tyrosines are cleaved, forming the thyroid hormones T 4 , T 3 , DIT, MIT, and traces of reverse triiodothyronine . T 3 and T 4 are released into

5785-413: The left side and occasionally separated. The pyramidal lobe is also known as Lalouette's pyramid. The pyramidal lobe is a remnant of the thyroglossal duct , which usually wastes away during the thyroid gland's descent. Small accessory thyroid glands may in fact occur anywhere along the thyroglossal duct, from the foramen cecum of the tongue to the position of the thyroid in the adult. A small horn at

5874-414: The main role in thyroid function. They consist of a rim that has a rich blood supply, nerve and lymphatic presence, that surrounds a core of colloid that consists mostly of thyroid hormone precursor proteins called thyroglobulin , an iodinated glycoprotein . The core of a follicle is surrounded by a single layer of follicular cells. When stimulated by thyroid stimulating hormone (TSH), these secrete

5963-417: The most common cause is iodine deficiency . In iodine-deficient regions, hypothyroidism (due to iodine deficiency) is the leading cause of preventable intellectual disability in children. In iodine-sufficient regions, the most common cause of hypothyroidism is the autoimmune disorder Hashimoto's thyroiditis . The thyroid gland is a butterfly-shaped organ composed of two lobes, left and right, connected by

6052-422: The nodule produces excess thyroid hormones. A radioactive iodine uptake test can help reveal the activity and location of the cancer and metastases. Thyroid cancers are treated by removing the whole or part of thyroid gland . Radioactive Iodine-131 may be given to radioablate the thyroid. Thyroxine is given to replace the hormones lost and to suppress TSH production, as TSH may stimulate recurrence. With

6141-440: The normal position of the thyroid gland to below the sternum, around the airway or esophagus. Goitres may be associated with hyperthyroidism or hypothyroidism, relating to the underlying cause of the goitre. Thyroid function tests may be done to investigate the cause and effects of the goitre. The underlying cause of the goitre may be treated, however many goitres with no associated symptoms are simply monitored . Inflammation of

6230-438: 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. Neurohormones were first identified by Otto Loewi in 1921. He incubated a frog's heart (innervated with its vagus nerve attached) in

6319-449: The outer part of the thyroid lobes. The venous blood is drained via superior and middle thyroid veins , which drain to the internal jugular vein , and via the inferior thyroid veins . The inferior thyroid veins originate in a network of veins and drain into the left and right brachiocephalic veins . Both arteries and veins form a plexus between the two layers of the capsule of the thyroid gland. Lymphatic drainage frequently passes

6408-417: The parafollicular c-cells, they direct calcitonin synthesis— CALCA , and CALCB . General practitioners , and internal medicine specialists play a role in identifying and monitoring the treatment of thyroid disease. Endocrinologists and thyroidologists are thyroid specialists. Thyroid surgeons or otolaryngologists are responsible for the surgical management of thyroid disease. Excessive production of

6497-887: 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

6586-412: The receptor, leading to symptoms associated with hypothyroidism. In addition, gradual protrusion of the eyes may occur, called Graves' ophthalmopathy , as may swelling of the front of the shins. Graves' disease can be diagnosed by the presence of pathomnomonic features such as involvement of the eyes and shins, or isolation of autoantibodies, or by results of a radiolabelled uptake scan. Graves' disease

6675-491: The release of calcium from bone, by decreasing the activity of osteoclasts , cells which break down bone. Bone is constantly reabsorbed by osteoclasts and created by osteoblasts , so calcitonin effectively stimulates movement of calcium into bone . The effects of calcitonin are opposite those of the parathyroid hormone (PTH) produced in the parathyroid glands. However, calcitonin seems far less essential than PTH, since calcium metabolism remains clinically normal after removal of

6764-422: The result of a large number of causes, including iodine deficiency, autoimmune disease (both Graves' disease and Hashimoto's thyroiditis), infection, inflammation, and infiltrative disease such as sarcoidosis and amyloidosis . Sometimes no cause can be found, a state called "simple goitre". Some forms of goitre are associated with pain, whereas many do not cause any symptoms. Enlarged goitres may extend beyond

6853-415: The sample undergoes cytology , in which the appearance of cells is viewed to determine whether they resemble normal or cancerous cells. The presence of multiple nodules is called a multinodular goitre ; and if it is associated with hyperthyroidism, it is called a toxic multinodular goitre . An enlarged thyroid gland is called a goitre . Goitres are present in some form in about 5% of people, and are

6942-411: The size and shape of the thyroid gland, and in the position of the embedded parathyroid glands. Sometimes there is a third lobe present called the pyramidal lobe . When present, this lobe often stretches up to the hyoid bone from the thyroid isthmus and may be one to several divided lobes. The presence of this lobe ranges in reported studies from 18.3% to 44.6%. It was shown to more often arise from

7031-419: The stomach, and insulin from the pancreas . 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

7120-409: 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

7209-461: The thyroid ( thyroidectomy ), but not the parathyroid glands . About 20,000 protein-coding genes are expressed in human cells: 70% of these genes are expressed in thyroid cells. Two-hundred and fifty of these genes are more specifically expressed in the thyroid, and about 20 genes are highly thyroid specific. In the follicular cells, the proteins synthesized by these genes direct thyroid hormone synthesis— thyroglobulin , TPO , and IYD ; while in

7298-403: The thyroid hormones T 3 and T 4 . They do this by transporting and metabolising the thyroglobulin contained in the colloid. Follicular cells vary in shape from flat to cuboid to columnar, depending on how active they are. The follicular lumen is the fluid-filled space within a follicle of the thyroid gland. There are hundreds of follicles within the thyroid gland. A follicle is formed by

7387-977: The thyroid hormones is called hyperthyroidism . Causes include Graves' disease , toxic multinodular goitre , solitary thyroid adenoma , inflammation, and a pituitary adenoma which secretes excess TSH. Another cause is excess iodine availability, either from excess ingestion, induced by the drug amiodarone , or following iodinated contrast imaging . Hyperthyroidism often causes a variety of non-specific symptoms including weight loss, increased appetite, insomnia, decreased tolerance of heat, tremor, palpitations , anxiety and nervousness. In some cases it can cause chest pain , diarrhoea , hair loss and muscle weakness. Such symptoms may be managed temporarily with drugs such as beta blockers . Long-term management of hyperthyroidism may include drugs that suppress thyroid function such as propylthiouracil , carbimazole and methimazole . Alternatively, radioactive iodine-131 can be used to destroy thyroid tissue: radioactive iodine

7476-533: The thyroid is called thyroiditis , and may cause symptoms of hyperthyroidism or hypothyroidism. Two types of thyroiditis initially present with hyperthyroidism and are sometimes followed by a period of hypothyroidism – Hashimoto's thyroiditis and postpartum thyroiditis . There are other disorders that cause inflammation of the thyroid, and these include subacute thyroiditis , acute thyroiditis , silent thyroiditis , Riedel's thyroiditis and traumatic injury, including palpation thyroiditis . Hashimoto's thyroiditis

7565-409: The thyroid is the production of the iodine-containing thyroid hormones , triiodothyronine (T 3 ) and thyroxine or tetraiodothyronine (T 4 ) and the peptide hormone calcitonin . The thyroid hormones are created from iodine and tyrosine . T 3 is so named because it contains three atoms of iodine per molecule and T 4 contains four atoms of iodine per molecule. The thyroid hormones have

7654-411: The thyroid. In this region, the recurrent laryngeal nerve and the inferior thyroid artery pass next to or in the ligament. Typically, four parathyroid glands , two on each side, lie on each side between the two layers of the thyroid capsule, at the back of the thyroid lobes. The thyroid gland is covered by a thin fibrous capsule, which has an inner and an outer layer. The inner layer extrudes into

7743-408: The two adrenal glands are all endocrine glands. Exocrine glands secrete their products through a duct onto an outer or inner surface of the body, such as the skin or the gastrointestinal tract . Secretion is directly onto the apical surface. The glands in this group can be divided into three groups: Exocrine glands can further be categorized by their product: Adenosis is any disease of

7832-530: 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., and these theories held sway until

7921-447: 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. Endocrinology involves caring for

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