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Encyclopedia > Thyroid
Thyroid
Endocrine system
Thyroid and parathyroid.
Latin glandula thyroidea
Gray's subject #272 1269
System endocinal jubachina system
Artery superior thyroid artery, inferior thyroid artery,
Vein superior thyroid vein, middle thyroid vein, inferior thyroid vein, thyreoidea ima
Nerve middle cervical ganglion, inferior cervical ganglion
Precursor 4th Branchial pouch
MeSH Thyroid+Gland
Dorlands/Elsevier g_06/12392768

The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck just below the Adam's apple. The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones. Image File history File links Illu_endocrine_system. ... Image File history File links Illu_thyroid_parathyroid. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... In biology, an organ is a group of tissues which perform some function. ... Section of an artery For other uses, see Artery (disambiguation). ... The superior thyroid artery arises from the external carotid artery just below the level of the greater cornu of the hyoid bone and ends in the thyroid gland. ... The inferior thyroid artery passes upward, in front of the vertebral artery and Longus colli; then turns medialward behind the carotid sheath and its contents, and also behind the sympathetic trunk, the middle cervical ganglion resting upon the vessel. ... In the circulatory system, a vein is a blood vessel that carries blood toward the heart. ... The Superior Thyroid Vein begins in the substance and on the surface of the thyroid gland, by tributaries corresponding with the branches of the superior thyroid artery, and ends in the upper part of the internal jugular vein. ... This article or section is in need of attention from an expert on the subject. ... The inferior thyroid veins two, frequently three or four, in number, arise in the venous plexus on the thyroid gland, communicating with the middle and superior thyroid veins. ... The thyreoidea ima ascends in front of the trachea to the lower part of the thyroid gland, which it supplies. ... Nerves (yellow) Nerves redirects here. ... The middle cervical ganglion is the smallest of the three cervical ganglia, and is occasionally absent. ... It has been suggested that this article or section be merged into cervical ganglia. ... This article or section is in need of attention from an expert on the subject. ... Pharyngeal or branchial pouches form on the endodermal side between the branchial arches, and pharyngeal grooves (or clefts) form from the lateral ectodermal surface of the neck region to separate the arches. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Elseviers logo. ... The cartilages of the larynx. ... This article or section does not cite any references or sources. ... A human neck. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Hormone is also the NATO reporting name for the Soviet/Russian Kamov Ka-25 military helicopter. ...


The thyroid participates in these processes by producing thyroid hormones, principally thyroxine (T4) and triiodothyronine (T3). These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Iodine is an essential component of both T3 and T4. The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis. Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... A few of the metabolic pathways in a cell. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Standard atomic weight 126. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. ...


The thyroid is controlled by the hypothalamus and pituitary. The gland gets its name from the Greek word for "shield", after its shape, a double-lobed structure. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland. Specialists are called Thyroidologists. The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). ... Located at the base of the skull, the pituitary gland is protected by a bony structure called the sella turcica. ... Hyperthyroidism (or overactive thyroid gland) is the clinical syndrome caused by an excess of circulating free thyroxine (T4) or free triiodothyronine (T3), or both. ... This article or section does not cite its references or sources. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ...

Contents

Anatomy

The thyroid is situated on the anterior side of the neck, starting at the oblique line on the thyroid cartilage (just below the laryngeal prominence or Adam's apple), and extending to the 6th Tracheal ring (C-shaped cartilagenous ring of the trachea). Vertebral levels are inappropriate to demarcate the gland's upper and lower border with vertebral levels as it moves position in relation to these during swallowing. It lies over the trachea and is covered by layers of pretracheal fascia (allowing it to move), muscle and skin. The cartilages of the larynx. ... For other uses, see Adams apple (disambiguation). ... The trachea, or windpipe, is a tube that has an inner diameter of about 12mm and a length of about 10-16cm. ... Fascia is specialized connective tissue layer which surrounds muscles, bones, and joints, providing support and protection and giving structure to the body. ...


The thyroid is one of the larger endocrine glands - 10-20 grams in adults and butterfly-shaped. The wings correspond to the lobes and the body to the isthmus of the thyroid. The isthmus overlies tracheal rings 2, 3 and 4. The thyroid may enlarge substantially during pregnancy and when affected by a variety of diseases.


Embryologic development

Floor of pharynx of embryo between 18 and 21 days.
Floor of pharynx of embryo between 18 and 21 days.

The thyroid is derived from the third pharyngeal pouch. In the fetus, at 3-4 weeks of gestation, 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 at a point latter indicated by the foramen cecum. Subsequently the thyroid descends in front of the pharyngeal gut as a bilobed diverticulum through the thyroglossal duct. Over the next few weeks, it migrates to the base of the neck. During migration, the thyroid remains connected to the tongue by a narrow canal, the thyroglossal duct. Image File history File links Gray42. ... Image File history File links Gray42. ... A pharyngeal pouch is a pulsion diverticulum of the pharyngeal mucosa through Killians dehiscence. ... Pattern of the branchial arches. ... The furcula is at first separated from the tuberculum impar by a depression, but later by a ridge, the copula, formed by the forward growth and fusion of the ventral ends of the second and third branchial arches. ... Foramen cecum can refer to: Foramen cecum (frontal bone) Foramen cecum (tongue) Foramen cecum (medulla oblongata) Category: ... The thyroglossal duct is an embryological anatomical structure which forms the connection between the initial area of development of the thyroid gland and its final position. ... The thyroglossal duct is an embryological anatomical structure which forms the connection between the initial area of development of the thyroid gland and its final position. ...


Follicles of the thyroid begin to make colloid in the 11th week and thyroxine by the 18th week.


Histology of the thyroid

At a histological level, there are three primary features of the thyroid:

Feature Description
Follicles The thyroid is composed of spherical follicles that selectively absorb iodine (as iodide ions, I-) from the blood for production of thyroid hormones. Twenty-five percent of all the body's iodide ions are in the thyroid gland. Inside the follicles, colloids rich in a protein called thyroglobulin serve as a reservoir of materials for thyroid hormone production and, to a lesser extent, act as a reservoir for the hormones themselves.
Thyroid epithelial cells
(or "follicular cells")
The follicles are surrounded by a single layer of thyroid epithelial cells, which secrete T3 and T4.
Parafollicular cells
(or "C cells")
Scattered among follicular cells and in spaces between the spherical follicles are another type of thyroid cell, parafollicular cells, which secrete calcitonin.

General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Standard atomic weight 126. ... In general, a colloid or colloidal dispersion is a substance with components of one or two phases, a type of mixture intermediate between a homogeneous mixture (also called a solution) and a heterogeneous mixture with properties also intermediate between the two. ... Thyroglobulin is a protein secreted by the thyroid gland. ... Thyroid epithelial cells are cells in the thyroid gland which produce and secrete thyroxine and triiodothyronine. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... Parafollicular cells also called C cells, are cells in the thyroid which produce and secrete calcitonin. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ...

Physiology

The primary function of the thyroid is production of the hormones thyroxine (T4), triiodothyronine (T3), and calcitonin. Up to 80% of the T4 is converted to T3 by peripheral organs such as the liver, kidney and spleen. T3 is about ten times more active than T4[1]. Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... The liver is an organ present in vertebrates and some other animals. ... The kidneys are organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. ... The spleen is an organ located the abdomen, where it functions in the destruction of old white blood cells and holding a reservoir of blood. ...


T3 and T4 production and action

Thyroxine is synthesised by the follicular cells from free tyrosine and on the tyrosine residues of the protein called thyroglobulin (TG). Iodine, captured with the "iodine trap" by the hydrogen peroxide generated by the enzyme thyroid peroxidase (TPO)[2] and linked to the 3' and 5' sites of the benzene ring of the tyrosine residues on TG, and on free tyrosine. Upon stimulation by the thyroid-stimulating hormone (TSH), the follicular cells reabsorb TG and proteolytically cleave the iodinated tyrosines from TG, forming T4 and T3 (in T3, one iodine is absent compared to T4), and releasing them into the blood. Deiodinase enzymes convert T4 to T3[3]. Thyroid hormone that is secreted from the gland is about 90% T4 and about 10% T3[1]. The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... Tyrosine (from the Greek tyros, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in cheese[1][2]), 4-hydroxyphenylalanine, or 2-amino-3(4-hydroxyphenyl)-propanoic acid, is one of the 20 amino acids that are used by cells to synthesize proteins. ... Tyrosine (from the Greek tyros, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in cheese[1][2]), 4-hydroxyphenylalanine, or 2-amino-3(4-hydroxyphenyl)-propanoic acid, is one of the 20 amino acids that are used by cells to synthesize proteins. ... Thyroglobulin is a protein secreted by the thyroid gland. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Standard atomic weight 126. ... Hydrogen peroxide (H2O2) is a very pale blue liquid which appears colourless in a dilute solution, slightly more viscous than water. ... Thyroid peroxidase is an enzyme (EC 1. ... Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. ... Proteases (proteinases, peptidases, or proteolytic enzymes) are enzymes that break peptide bonds between amino acids of proteins. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ...


Cells of the brain are a major target for the thyroid hormones T3 and T4. Thyroid hormones play a particularly crucial role in brain development during pregnancy[4]. A transport protein (OATP1C1) has been identified that seems to be important for T4 transport across the blood brain barrier[5]. A second transport protein (MCT8) is important for T3 transport across brain cell membranes[5]. The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The blood-brain barrier is a physical barrier between the blood vessels in the central nervous system, and the central nervous system itself. ...


In the blood, T4 and T3 are partially bound to thyroxine-binding globulin, transthyretin and albumin. Only a very small fraction of the circulating hormone is free (unbound) - T4 0.03% and T3 0.3%. Only the free fraction has hormonal activity. As with the steroid hormones and retinoic acid, thyroid hormones cross the cell membrane and bind to intracellular receptors1, α2, β1 and β2), which act alone, in pairs or together with the retinoid X-receptor as transcription factors to modulate DNA transcription[1]. Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroxine-binding globulin (TBG) or transthyretin is the major binding protein of thyroid hormones in the bloodstream. ... Transthyretin (TTR) is a serum and cerebrospinal fluid carrier of the thyroid hormone thyroxine (T4). ... You may be looking for albumen, or egg white. ... Steroid hormones are steroids which act as hormones. ... Retinoic acid, or Retin-A or vitamin A acid, is a carotenoid organic compound that is a component of visual pigments. ... The cell membrane (also called the plasma membrane, plasmalemma or phospholipid bilayer) is a semipermeable lipid bilayer common to all living cells. ... Intracellular receptors or nuclear receptors are a class of receptor located inside the cell rather than on its cell membrane. ... There are three forms of retinoid X receptor (RXR), RXR-alpha, RXR-beta, and RXR-gamma. ... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... In genetics, transcription is the first of the two-step protein biosynthesis process. ...


T3 and T4 regulation

The production of thyroxine and triiodothyronine is regulated by thyroid-stimulating hormone (TSH), released by the anterior pituitary. The thyroid and thyrotropes form a negative feedback loop: TSH production is suppressed when the T4 levels are high, and vice versa. The TSH production itself is modulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus and secreted at an increased rate in situations such as cold (in which an accelerated metabolism would generate more heat). TSH production is blunted by somatostatin (SRIH), rising levels of glucocorticoids and sex hormones (estrogen and testosterone), and excessively high blood iodide concentration. The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. ... The anterior pituitary (also called the adenohypophysis) comprises the anterior lobe of the pituitary gland and is part of the endocrine system. ... Thyrotropes are cells in the anterior pituitary which produce thyroid stimulating hormone. ... This article does not cite any references or sources. ... Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. ... Thyrotropin-releasing hormone (TRH), also called thyrotropin-releasing factor (TRF) or protirelin, is a tripeptide hormone that stimulates the release of thyroid-stimulating hormone and prolactin by the anterior pituitary. ... The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). ... Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. ... Somatostatin is a hormone. ... Glucocorticoids are a class of steroid hormones characterised by an ability to bind with the cortisol receptor and trigger similar effects. ... Sex hormones are hormones that affect the reproductive system. ... Estriol. ... Testosterone is a steroid hormone from the androgen group. ...


Calcitonin

An additional hormone produced by the thyroid contributes to the regulation of blood calcium levels. Parafollicular cells produce calcitonin in response to hypercalcemia. Calcitonin stimulates movement of calcium into bone, in opposition to the effects of parathyroid hormone (PTH). However, calcitonin seems far less essential than PTH, as calcium metabolism remains clinically normal after removal of the thyroid, but not the parathyroids. Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. ... Parafollicular cells (also called C cells) are cells in the thyroid which produce and secrete calcitonin. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... Hypercalcaemia is an elevated calcium level in the blood. ... Grays Anatomy illustration of a human femur. ... Parathyroid hormone (PTH) is secreted by the parathyroid glands as a polypeptide containing 84 amino acids. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... Parathyroid hormone (PTH) is secreted by the parathyroid glands as a polypeptide containing 84 amino acids. ... Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. ... The parathyroid glands are small endocrine glands in the neck, usually located behind the thyroid gland, which produce parathyroid hormone. ...


It may be used diagnostically as a tumor marker for a form of thyroid cancer (medullary thyroid adenocarcinoma), in which high calcitonin levels may be present and elevated levels after surgery may indicate recurrence. It may even be used on biopsy samples from suspicious lesions (e.g. swollen lymph nodes) to establish whether they are metastasis of the original cancer. Tumor markers are substances found in the blood, urine or body tissues that can be elevated in cancer. ... Thyroid cancer is malignant growth of the thyroid gland. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... Brain biopsy A biopsy (in Greek: bios = life and opsy = look/appearance) is a medical test involving the removal of cells or tissues for examination. ... Lymph nodes are components of the lymphatic system. ... Metastasis (Greek: change of the state) is the spread of cancer from its primary site to other places in the body. ...


Calcitonin can be used therapeutically for the treatment of hypercalcemia or osteoporosis. Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... Hypercalcaemia is an elevated calcium level in the blood. ... Osteoporosis is a disease of bone in which the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. ...


The significance of iodine

In areas of the world where iodine (essential for the production of thyroxine, which contains four iodine atoms) is lacking in the diet, the thyroid gland can be considerably enlarged, resulting in the swollen necks of endemic goitre. Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... A goitre (or goiter) (Latin struma), also called a bronchocele, is a swelling in the neck (just below Adams apple or larynx) due to an enlarged thyroid gland. ...


Thyroxine is critical to the regulation of metabolism and growth throughout the animal kingdom. Among amphibians, for example, administering a thyroid-blocking agent such as propylthiouracil (PTU) can prevent tadpoles from metamorphosing into frogs; conversely, administering thyroxine will trigger metamorphosis. Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ... A few of the metabolic pathways in a cell. ... For other uses, see Amphibian (disambiguation). ... Propylthiouracil is a thioamide drug used to treat hyperthyroidism. ... Thyroxine, or 3:5,3:5 tetra­iodothyronine (often abbreviated as T4) is the major hormone secreted by the follicular cells of the thyroid gland. ...


In humans, children born with thyroid hormone deficiency will have physical growth and development problems, and brain development can also be severely impaired, in the condition referred to as cretinism. Newborn children in many developed countries are now routinely tested for thyroid hormone deficiency as part of newborn screening by analysis of a drop of blood. Children with thyroid hormone deficiency are treated by supplementation with synthetic thyroxine, which enables them to grow and develop normally. The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Cretinism (most likely from the Latin Christiānum, Christian) is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones (hypothyroidism). ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Newborn screening is the process of testing newborn babies for treatable genetic, endocrinologic, metabolic and hematologic diseases. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Levothyroxine, also known as L-thyroxine, synthetic T4 or simply 3,5,3,5-tetraiodo-L-thyronine, is a synthetic form of thyroxine (thyroid hormone). ...


Because of the thyroid's selective uptake and concentration of what is a fairly rare element, it is sensitive to the effects of various radioactive isotopes of iodine produced by nuclear fission. In the event of large accidental releases of such material into the environment, the uptake of radioactive iodine isotopes by the thyroid can, in theory, be blocked by saturating the uptake mechanism with a large surplus of non-radioactive iodine, taken in the form of potassium iodide tablets. While biological researchers making compounds labelled with iodine isotopes do this, in the wider world such preventive measures are usually not stockpiled before an accident, nor are they distributed adequately afterward. One consequence of the Chernobyl disaster was an increase in thyroid cancers in children in the years following the accident. [2] Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... For the generation of electrical power by fission, see Nuclear power plant An induced nuclear fission event. ... Potassium iodide is a white crystalline salt with chemical formula KI, used in photography and radiation treatment. ... Chernobyl area. ... Thyroid cancer is malignant growth of the thyroid gland. ...


The use of iodised salt is an efficient way to add iodine to the diet. It has eliminated endemic cretinism in most developed countries, and some governments have made the iodination of flour mandatory. Potassium iodide and Sodium iodide are the most active forms of supplemental iodine. Iodized table salt (left) and non-iodized table salt (right) The Morton Salt company began iodizing salt for Americans in the fall of 1924. ... Cretinism (most likely from the Latin Christiānum, Christian) is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones (hypothyroidism). ...


Diseases of the thyroid gland

Hyper- and hypofunction (affects about 2% of the population)

This article or section does not cite its references or sources. ... This disease was discovered by Mr. ... Thyroiditis is an inflammation of the thyroid gland. ... Postpartum thyroiditis is usually a transient phenomenon observed following pregnancy and may involve hyperthyroidism, hypothyroidism or the two sequentially. ... Silent thyroiditis, also known as painless thyroiditis or more specifically and scientifically as subacute lymphocytic thyroiditis, is a member of the group of thyroiditis conditions known as resolving thyroiditis. ... Hyperthyroidism (or overactive thyroid gland) is the clinical syndrome caused by an excess of circulating free thyroxine (T4) or free triiodothyronine (T3), or both. ... Graves-Basedow disease or known simply as Graves disease is a medical disorder that may manifest several different conditions including goitre and hyperthyroidism (over-activity of thyroid hormone production), infiltrative exophthalmos (protruberance of one or both eyes and associated problems) and infiltrative dermopathy (a skin condition usually of the lower... A thyroid adenoma, or solitary thyroid nodule is a benign tumor of the thyroid gland. ... Toxic multinodular goitre (or Toxic nodular goitre, or Toxic nodular struma, or Plummers disease) is a form of goitre that after Graves disease is the next most common cause of hyperthyroidism. ... An abscess on the skin, showing the redness and swelling characteristic of inflammation. ...

Anatomical problems

A goitre (or goiter) (Latin struma), also called a bronchocele, is a swelling in the neck (just below Adams apple or larynx) due to an enlarged thyroid gland. ... Endemic goitre is a type of goitre that is associated with dietary iodine deficiency. ... Wikipedia does not have an article with this exact name. ... A thyroglossal cyst is a fibrous cyst that forms from a persistent thyroglossal duct. ...

Tumors

A thyroid adenoma, or solitary thyroid nodule is a benign tumor of the thyroid gland. ... Thyroid cancer is malignant growth of the thyroid gland. ... This article is about lymphoma in humans. ... Metastasis (Greek: change of the state) is the spread of cancer from its primary site to other places in the body. ...

Deficiencies

Medication linked to thyroid disease includes amiodarone, lithium salts, some types of interferon and IL-2. Cretinism (most likely from the Latin Christiānum, Christian) is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones (hypothyroidism). ... Amiodarone belongs to a class of drugs called Vaughan-Williams Class III antiarrhythmic agent. ... Lithium salts are chemical salts of lithium used primarily in the treatment of bipolar disorder as mood stabilizing drugs. ... Interferons (IFNs) are natural proteins produced by the cells of the immune system of most vertebrates in response to challenges by foreign agents such as viruses, bacteria, parasites and tumor cells. ... Interleukin-2 (IL-2) is an interleukin, a type of biological response modifier, a substance that can improve the bodys natural response to disease. ...


Diagnosis

Blood tests

  • The measurement of thyroid-stimulating hormone (TSH) levels is often used by doctors as a screening test. Elevated TSH levels can signify an inadequate hormone production, while suppressed levels can point at excessive unregulated production of hormone.
  • If TSH is abnormal, decreased levels of thyroid hormones T4 and T3 may be present; these may be determined to confirm this.
  • Autoantibodies may be detected in various disease states (anti-TG, anti-TPO, TSH receptor stimulating antibodies).
  • There are two cancer markers for thyroid derived cancers. Thyroglobulin (TG) for well differentiated papillary or follcular adenocarcinoma, and the rare medullary thyroid cancer has calcitonin as the marker.
  • Very infrequently, TBG and transthyretin levels may be abnormal; these are not routinely tested.

The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... An autoantibody is an antibody (a type of protein) manufactured by the immune system that is directed against one or more of the individuals own proteins. ... Thyroglobulin is a protein secreted by the thyroid gland. ... Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. ... Thyroxine-binding globulin (TBG) or transthyretin is the major binding protein of thyroid hormones in the bloodstream. ... Transthyretin (TTR) is a serum and cerebrospinal fluid carrier of the thyroid hormone thyroxine (T4). ...

Ultrasound

Nodules of the thyroid may or may not be cancer. Medical ultrasonography can help determine their nature because some of the characteristics of benign and malignant nodules differ. The main characteristics of a thyroid nodule on high frequency thyroid ultrasound are as follows: Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... Medical ultrasonography (sonography) is an ultrasound-based diagnostic imaging technique used to visualize muscles and internal organs, their size, structures and possible pathologies or lesions. ...

Possible cancer Benign characteristics
irregular border smooth borders
hypoechoic (less echogenic than the surrounding tissue) hyperechoic
microcalcifications -
taller than wide shape on transverse study -
significant intranodular blood flow by power Doppler -
- "comet tail" artifact as sound waves bounce off intranodular colloid

Ultrasonography is not always able to separate benign from malignant nodules with complete certainty. In suspicious cases, a tissue sample is often obtained by biopsy for microscopic examination.


Radioiodine scanning and uptake

Thyroid scintigraphy, imaging of the thyroid with the aid of radioactive iodine, usually iodine-123 (123I), is performed in the nuclear medicine department of a hospital or clinic. Radioiodine collects in the thyroid gland before being excreted in the urine. While in the thyroid the radioactive emissions can be detected by a camera, producing a rough image of the shape (a radiodine scan) and tissue activity (a radioiodine uptake) of the thyroid gland. Nuclear medicine is the branch of medicine that uses unsealed radioactive substances in diagnosis and therapy. ... Iodine-123 is often used as a radioactive substance used in whole-body nuclear scanning. ... Shown above is the bone scintigraphy of a young woman. ...


A normal radioiodine scan shows even uptake and activity throughout the gland. Irregularity can reflect an abnormally shaped or abnormally located gland, or it can indicate that a portion of the gland is overactive or underactive, different from the rest. For example, a nodule that is overactive ("hot") to the point of suppressing the activity of the rest of the gland is usually a thyrotoxic adenoma, a surgically curable form of hyperthyroidism that is hardly ever malignant. In contrast, finding that a substantial section of the thyroid is inactive ("cold") may indicate an area of non-functioning tissue such as thyroid cancer.


The amount of radioactivity can be counted as an indicator of the metabolic activity of the gland. A normal quantitation of radioiodine uptake demonstrates that about 8 to 35% of the administered dose can be detected in the thyroid 24 hours later. Overactivity or underactivity of the gland as may occur with hypothyroidism or hyperthyroidism is usually reflected in decreased or increased radioiondine uptake. Different patterns may occur with different causes of hypo- or hyperthyroidism.


Biopsy

A medical biopsy refers to the obtaining of a tissue sample for examination under the microscope or other testing, usually to distinguish cancer from noncancerous conditions. Thyroid tissue may be obtained for biopsy by fine needle aspiration or by surgery. Brain biopsy A biopsy (in Greek: bios = life and opsy = look/appearance) is a medical test involving the removal of cells or tissues for examination. ... Needle aspiration biopsy is a procedure performed to diagnose and treat certain kind of illnesses. ... “Surgeon” redirects here. ...


Needle aspiration has the advantage of being a brief, safe, outpatient procedure that is safer and less expensive than surgery and does not leave a visible scar. Needle biopsies became widely used in the 1980s, but it was recognized that accuracy of identification of cancer was good but not perfect. The accuracy of the diagnosis depends on obtaining tissue from all of the suspicious areas of an abnormal thyroid gland. The reliability of needle aspiration is increased when sampling can be guided by ultrasound, and over the last 15 years, this has become the preferred method for thyroid biopsy in North America.


Treatment

Medical treatment

Levothyroxine is a stereoisomer of thyroxine which is degraded much slower and can be administered once daily in patients with hypothyroidism. Levothyroxine, also known as L-thyroxine, synthetic T4 or simply 3,5,3,5-tetraiodo-L-thyronine, is a synthetic form of thyroxine (thyroid hormone). ... Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ...


Graves' disease may be treated with the thioamide drugs propylthiouracil, carbimazole or methimazole, or rarely with Lugol's solution. Hyperthyroidism as well as thyroid tumors may be treated with radioactive iodine. General structure of a thioamide. ... Propylthiouracil is a thioamide drug used to treat hyperthyroidism. ... Carbimazole is used to treat hyperthyroidism. ... Methimazole is an antithyroid drug similar in action to propylthiouracil. ... Lugols iodine, also known as Lugols solution, is a solution of iodine named after the French physician J.G.A. Lugol. ... Iodine-131, also called radioiodine, is a radioisotope of iodine. ...


Percutaneous Ethanol Injections, PEI, for therapy of recurrent thyroid cysts, and metastatic thyroid cancer lymph nodes, as an alternative to the usual surgical method.


Thyroid surgery

Thyroid surgery is performed for a variety of reasons. A nodule or lobe of the thyroid is sometimes removed for biopsy or for the presence of an autonomously functioning adenoma causing hyperthyroidism. A large majority of the thyroid may be removed, a subtotal thyroidectomy, to treat the hyperthyroidism of Graves' disease, or to remove a goitre that is unsightly or impinges on vital structures. A complete thyroidectomy of the entire thyroid, including associated lymph nodes, is the preferred treatment for thyroid cancer. Removal of the bulk of the thyroid gland usually produces hypothyroidism, unless the person takes thyroid hormone replacement. Brain biopsy A biopsy (in Greek: bios = life and opsy = look/appearance) is a medical test involving the removal of cells or tissues for examination. ... A thyroid adenoma, or solitary thyroid nodule is a benign tumor of the thyroid gland. ... Hyperthyroidism (or overactive thyroid gland) is the clinical syndrome caused by an excess of circulating free thyroxine (T4) or free triiodothyronine (T3), or both. ... Graves-Basedow disease is a form of thyroiditis, an autoimmune disorder that stimulates the thyroid gland, being the most common cause of hyperthyroidism (overactivity of the thyroid). ... A goitre (or goiter) (Latin struma), also called a bronchocele, is a swelling in the neck (just below Adams apple or larynx) due to an enlarged thyroid gland. ... A thyroidectomy involves the surgical removal all or part of the thyroid gland. ... Lymph nodes are components of the lymphatic system. ... Thyroid cancer is malignant growth of the thyroid gland. ... This article or section does not cite its references or sources. ... The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ...


If the thyroid gland must be removed surgically, care must be taken to avoid damage to adjacent structures, the parathyroid glands and the recurrent laryngeal nerve. Both are susceptible to accidental removal and/or injury during thyroid surgery. The parathyroid glands produce parathyroid hormone (PTH), a hormone needed to maintain adequate amounts of calcium in the blood. Removal results in hypoparathyroidism and a need for supplemental calcium and vitamin D each day. The recurrent laryngeal nerves provide motor control for all external muscles of the larynx except for the cricothyroid muscle, also runs along the posterior thyroid. Accidental laceration of either of the two or both recurrent laryngeal nerves may cause paralysis of the vocal cords and their associated muscles, changing the voice quality. The four human parathyroid glands are adjacent to the thyroid. ... The recurrent laryngeal nerve is a branch of the vagus nerve (the tenth cranial nerve) that supplies motor function and sensation to the larynx (voice box). ... Parathyroid hormone (PTH) is secreted by the parathyroid glands as a polypeptide containing 84 amino acids. ... In medicine (endocrinology), hypoparathyroidism is decreased function of the parathyroid glands, leading to decreased levels of parathyroid hormone (PTH). ... Vitamin D is a fat soluble vitamin that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. ... The larynx (plural larynges), colloquially known as the voicebox, is an organ in the neck of mammals involved in protection of the trachea and sound production. ... The cricothyroid muscle attaches to the anterolateral aspect of the cricoid and the inferior cornu and lower lamina of the thyroid cartilage, tilting the thyroid forwards and lengthening the vocal cords. ... Laryngoscopic view of the vocal folds. ...


Radioiodine therapy

Large goiters that cause symptoms, but do not harbor cancer, after evaluation, and biopsy of suspicious nodules can be treated by an alternative therapy with radioiodine. The iodine uptake can be high in countries with iodine deficiency, but low in iodine sufficient countries. The 1999 release of rhTSH thyrogen in the USA, can boost the uptakes to 50-60% allowing the therapy with iodine 131. The gland shrinks by 50-60%, but can cause hypothyroidism, and rarely pain syndrome cause by radiation thyroiditis that is short lived and treated by steroids.


History

There are several findings that evidence a great interest for thyroid disorders just in the Medieval Medical School of Salerno (XII Century). Rogerius Salernitanus, the Salernitan surgeon and author of "Post mundi fabricam" (around 1180) was considered at that time the surgical text par excellence all over Europe. In the chapter "De bocio" of his magnus opum he describes several pharmacological and surgical cures, some of which nowadays are reappraised quite scientifically effective.[6] Salerno is a town in Campania, south-western Italy, the capital of the province of the same name. ... Detail from Rogerius treatise (Amiens, ca. ...


In modern times, the thyroid was first identified by the anatomist Thomas Wharton (whose name is also eponymised in Wharton's duct of the submandibular gland) in 1656.[7] Human heart and lungs, from an older edition of Grays Anatomy. ... An eponym is the name of a person, whether real or fictitious, who has (or is thought to have) given rise to the name of a particular place, tribe, discovery, or other item. ... The submaxillary duct (Whartons duct, Submandibular duct) is about 5 cm. ...


Thyroid hormone (or thyroxin) was only identified in the 19th century. The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are tyrosine-based hormones produced by the thyroid gland. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ...


Additional images

See also

Thymus, see Thyme. ... This article or section does not cite its references or sources. ...

References

  1. ^ a b The thyroid gland in Endocrinology: An Integrated Approach by Stephen Nussey and Saffron Whitehead (2001) Published by BIOS Scientific Publishers Ltd. ISBN 1-85996-252-1 .
  2. ^ Ekholm R, Bjorkman U (1997). "Glutathione peroxidase degrades intracellular hydrogen peroxide and thereby inhibits intracellular protein iodination in thyroid epithelium". Endocrinology 138 (7): 2871-2878. PMID 9202230. 
  3. ^ Bianco AC, Salvatore D, Gereben B, Berry MJ, Larsen PR (2002). "Biochemistry, cellular and molecular biology, and physiological roles of the iodothyronine selenodeiodinases". Endocr Rev 23 (1): 38-89. PMID 11844744. 
  4. ^ Kester MH, Martinez de Mena R, Obregon MJ, Marinkovic D, Howatson A, Visser TJ, Hume R, Morreale de Escobar G (2004). "Iodothyronine levels in the human developing brain: major regulatory roles of iodothyronine deiodinases in different areas". J Clin Endocrinol Metab 89 (7): 3117-3128. PMID 15240580. 
  5. ^ a b Jansen J, Friesema ECH, Milici C, Visser TJ (2005). Thyroid hormone transporters in health and disease. Thyroid 15;757-768. PMID 16131319.
  6. ^ Bifulco M, Cavallo P. Thyroidology in the medieval medical school of salerno. Thyroid 2007;17:39-40. PMID 17274747.
  7. ^ Thomas Wharton at Who Named It

Who Named It is a Norwegian database of several thousand eponymous medical signs and the doctors associated with their identification. ...

External links


  Results from FactBites:
 
Thyroid - Wikipedia, the free encyclopedia (1732 words)
The thyroid is one of the larger endocrine glands - 10-20 grams in adults- and butterfly-shaped: the wings correspond to the lobes and the body to the isthmus of the thyroid.
The superior thyroid artery is the first branch of the external carotid, and supplies mostly the upper half of the thyroid gland, while the inferior thyroid artery is the major branch of the thyrocervical trunk, which comes off of the subclavian artery.
A nodule or lobe of the thyroid is sometimes removed for biopsy or for the presence of an autonomously functioning adenoma causing hyperthyroidism.
Thyroid cancer - Wikipedia, the free encyclopedia (2383 words)
Thyroid cancer is cancer of the thyroid gland.
As the thyroid concentrates iodine, radioactive iodine is a commonly used modality in thyroid carcinomas.
"Usefulness of fine-needle aspiration in the diagnosis of thyroid carcinoma".
  More results at FactBites »

 
 

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