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, thyreoidea ima
Vein	superior thyroid vein, middle thyroid vein, inferior thyroid vein
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. Endocrine glands are Glands that secrete their product ( Hormones, directly into the blood rather than through a duct This gland is found in the neck inferior to (below) the thyroid cartilage (also known as the Adam's apple in men) and at approximately the same level as the cricoid cartilage. The neck is the part of the Body on many limbed Vertebrates that distinguishes the head from the Torso or trunk The thyroid cartilage is the largest of the nine Cartilages that make up the laryngeal skeleton, the cartilage structure in and around the trachea that contains The cricoid cartilage, or simply cricoid (from the Greek krikoeides meaning "ring-shaped" is the only complete ring of Cartilage around the The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body

The thyroid participates in these processes by producing thyroid hormones, principally thyroxine (T₄) and triiodothyronine (T₃). Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Iodine is an essential component of both T₃ and T₄. Iodine (ˈaɪədaɪn ˈaɪədɪn or /ˈaɪədiːn/ from ιώδης iodes "violet" is a Chemical element that has the symbol I and Atomic The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis. Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the 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 hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis The pituitary gland, or hypophysis, is an Endocrine gland about the size of a Pea. The gland gets its name from the Greek word for "shield", after the shape of the related thyroid cartilage. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland. Hyperthyroidism is the term for overactive tissue within the Thyroid gland resulting in overproduction and thus an excess of circulating free thyroid hormones Thyroxine Hypothyroidism is the disease state in humans and animals caused by insufficient production of Thyroid hormone by the Thyroid gland.

Anatomy

The thyroid gland is a butterfly-shaped organ and is composed of two cone-like lobes or wings: lobus dexter (right lobe) and lobus sinister (left lobe), connected with the isthmus. The Thyroid isthmus connects together the lower thirds of the lobes it measures about 1 The organ is situated on the anterior side of the neck, lying against and around the larynx and trachea, reaching posteriorly the oesophagus and carotid sheath. The larynx (plural larynges) colloquially known as the voicebox, is an organ in the Neck of Mammals involved in protection of the The traceartes, or windpipe, is a tube that has an inner diameter of about 20-25 mm and a length of about 10-16 cm in humans The esophagus or oesophagus (see American and British English spelling differences) sometimes known as the gullet, is an organ in The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the Internal carotid artery and related structures in the neck It starts cranially at the oblique line on the thyroid cartilage (just below the laryngeal prominence or Adam's apple) and extends inferiorly to the fourth to sixth tracheal ring. The thyroid cartilage is the largest of the nine Cartilages that make up the laryngeal skeleton, the cartilage structure in and around the trachea that contains The cartilages of the trachea (or tracheal rings) vary from sixteen to twenty in number each forms an imperfect ring which occupies the anterior two-thirds or so of the circumference It is difficult to demarcate the gland's upper and lower border with vertebral levels as it moves position in relation to these during swallowing.

The thyroid gland is covered by a fibrous sheath, the capsula glandulae thyroidea, composed of an internal and external layer. The external layer is anteriorly continuous with the lamina pretrachealis fasciae cervicalis and posteriorolaterally continuous with the carotid sheath. The pretracheal fascia extends medially in front of the Carotid vessels, and assists in forming the Carotid sheath. The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the Internal carotid artery and related structures in the neck The gland is covered anteriorly with infrahyoid muscles and laterally with the sternocleidomastoid muscle. The infrahyoid muscles are a group of four pairs of Muscles in the anterior part of the Neck. In Human Anatomy, the sternocleidomastoid (pronounced /ˌstɚ Posteriorly, the gland is fixed to the cricoid and tracheal cartilage and cricopharyngeus muscle by a thickening of the fascia to form the posterior suspensory ligament of Berry^[1][2]. The cricoid cartilage, or simply cricoid (from the Greek krikoeides meaning "ring-shaped" is the only complete ring of Cartilage around the The traceartes, or windpipe, is a tube that has an inner diameter of about 20-25 mm and a length of about 10-16 cm in humans The Inferior pharyngeal constrictor, the thickest of the three constrictors arises from the sides of the Cricoid and Thyroid cartilage. In variable extent, Zuckerkandl's tubercle, a pyramidal extension of the thyroid lobe, is present at the most posterior side of the lobe^[3][4]. Zuckerkandl's tubercle is a pyramidal extension of the Thyroid gland, present at the most posterior side of each lobe In this region the recurrent laryngeal nerve and the inferior thyroid artery pass next to or in the ligament and tubercle. The recurrent (inferior laryngeal nerve is a branch of the vagus nerve (tenth Cranial nerve) that supplies motor function and sensation to the Larynx (voice box Between the two layers of the capsule and on the posterior side of the lobes there are on each side two parathyroid glands. The parathyroid glands are small endocrine Glands in the neck usually located behind the Thyroid gland, which produce Parathyroid hormone.

The thyroid isthmus is variable in presence and size, and can encompass a cranially extending pyramid lobe (lobus pyramidalis or processus pyramidalis), remnant of the thyroglossal duct. The Thyroid isthmus connects together the lower thirds of the lobes it measures about 1 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 The thyroid is one of the larger endocrine glands, weighing 2-3 grams in neonates and 18-60 grams in adults, and is increased in pregnancy.

The thyroid 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 the thyroid ima artery, branching directly from the aortic arch. 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 In Human anatomy, the external carotid artery is a major Artery of the head and neck 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 The thyrocervical trunk is a branch of the Subclavian artery arising from the first portion of this vessel i The thyroidea ima ascends in front of the trachea to the lower part of the Thyroid gland, which it supplies The venous blood is drained via superior thyroid veins, draining in the internal jugular vein, and via inferior thyroid veins, draining via the plexus thyroideus impar in the left brachiocephalic vein. 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 The internal jugular vein collects the blood from the Brain, the superficial parts of the Face, and the Neck. 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 The left and right brachiocephalic veins (or Innominate veins) in the upper chest are formed by the union of each corresponding Internal jugular vein and Lymphatic drainage passes frequently the lateral deep cervical lymph nodes and the pre- and parathracheal lymph nodes. Cervical lymph nodes are Lymph nodes found in the neck Classification There are approximately 300 lymph nodes in the neck and they can be classified in many Cervical lymph nodes are Lymph nodes found in the neck Classification There are approximately 300 lymph nodes in the neck and they can be classified in many The gland is supplied by sympathetic nerve input from the superior cervical ganglion and the cervicothoracic ganglion of the sympathetic trunk, and by parasympathetic nerve input from the superior laryngeal nerve and the recurrent laryngeal nerve. The superior cervical ganglion (SCG the largest of the cervical ganglia is placed opposite the second and third Cervical vertebræ. The stellate ganglion (or cervicothoracic ganglion) is a Sympathetic ganglion formed by the fusion of the Inferior cervical ganglion and the first thoracic The sympathetic trunks ( sympathetic chain, gangliated cord) are a paired bundle of nerve fibers that run from the base of the Skull to the Coccyx The parasympathetic Nervous system ( PSNS) is a division of the Autonomic nervous system (ANS along with the Sympathetic nervous system The superior laryngeal nerve is a branch of the Vagus nerve. It arises from the middle of the Ganglion nodosum and in its course receives a branch from the Superior The recurrent (inferior laryngeal nerve is a branch of the vagus nerve (tenth Cranial nerve) that supplies motor function and sensation to the Larynx (voice box

Embryological development

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. During the third week of embryological development there appears immediately behind the ventral ends of the two halves of the Mandibular arch, a rounded swelling named the tuberculum Also known as the Hypobranchial eminence. The Furcula is at first separated from the Tuberculum impar by a depression but later by a ridge the copula The dorsum of the Tongue is convex and marked by a median sulcus which divides it into symmetrical halves this sulcus ends behind about 2 Subsequently the thyroid descends in front of the pharyngeal gut as a bilobed diverticulum through the thyroglossal duct. 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 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. 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 Follicles of the thyroid begin to make colloid in the 11th week and thyroxine by the 18th week.

Histology

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

Physiology

The primary function of the thyroid is production of the hormones thyroxine (T4), triiodothyronine (T3), and calcitonin. Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the Up to 80% of the T4 is converted to T3 by peripheral organs such as the liver, kidney and spleen. The liver is a vital organ in the human body and is present in Vertebrates and some other animals The kidneys are complicated organs that have numerous biological roles The spleen is an organ found in all Vertebrate animals In humans the spleen is located in the abdomen of the body where it functions in the destruction of redundant Red T3 is about ten times more active than T4. ^[5]

T3 and T4 production and action

Thyroxine (T4) is synthesised by the follicular cells from free tyrosine and on the tyrosine residues of the protein called thyroglobulin (TG). Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 Amino acids that are used by cells to synthesize Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 Amino acids that are used by cells to synthesize Thyroglobulin (Tg is a 660 kDa dimeric Protein produced by and used entirely within the Thyroid gland Iodine is captured with the "iodine trap" by the hydrogen peroxide generated by the enzyme thyroid peroxidase (TPO)^[6] and linked to the 3' and 5' sites of the benzene ring of the tyrosine residues on TG, and on free tyrosine. Iodine (ˈaɪədaɪn ˈaɪədɪn or /ˈaɪədiːn/ from ιώδης iodes "violet" is a Chemical element that has the symbol I and Atomic Hydrogen peroxide (H2O2 is a very pale blue liquid which appears colorless in a dilute solution slightly more Viscous than water Thyroid peroxidase or Thyroperoxidase (TPO is an Enzyme mainly expressed in the Thyroid that liberates Iodine for addition onto 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. Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a Peptide hormone synthesized and secreted by Thyrotrope cells in the A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products Deiodinase enzymes convert T4 to T3. Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid ^[7] Thyroid hormone that is secreted from the gland is about 90% T4 and about 10% T3. ^[5]

Cells of the brain are a major target for the thyroid hormones T3 and T4. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Thyroid hormones play a particularly crucial role in brain development during pregnancy. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced ^[8] A transport protein (OATP1C1) has been identified that seems to be important for T4 transport across the blood brain barrier. Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the The blood-brain barrier (BBB is a metabolic or cellular structure in the Central nervous system (CNS that restricts the passage of various chemical substances and microscopic ^[9] A second transport protein (MCT8) is important for T3 transport across brain cell membranes. ^[9]

In the blood, T4 and T3 are partially bound to thyroxine-binding globulin, transthyretin and albumin. Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid Thyroxine-binding globulin (TBG binds Thyroid hormone in circulation Transthyretin (TTR is a serum and Cerebrospinal fluid carrier of the Thyroid Hormone Thyroxine (T4 Serum albumin, often referred to simply as albumin, is the most abundant Plasma protein in humans and other Mammals Albumin is essential for maintaining 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 receptors (α₁, α₂, β₁ and β₂), which act alone, in pairs or together with the retinoid X-receptor as transcription factors to modulate DNA transcription[2]. Steroid hormones are Steroids which act as Hormones Mammalian steroid hormones can be grouped into five groups by the receptors to which they bind Retinol (Afaxin, the animal form of Vitamin A, is a fat-soluble vitamin important in vision and Bone growth The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer Intracellular receptors are receptors located inside the cell rather than on its Cell membrane. The retinoid X receptor ( RXR) is a type of Nuclear receptor which is activated by 9-cis retinoic acid. In the field of Molecular biology, a transcription factor (sometimes called a sequence-specific DNA binding factor is a Protein that binds to specific sequences Transcription is the synthesis of RNA under the direction of DNA

T3 and T4 regulation

The production of thyroxine and triiodothyronine is regulated by thyroid-stimulating hormone (TSH), released by the anterior pituitary (that is in turn released as a result of TRH release by the hypothalamus). Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Triiodothyronine, C15[[hydrogen H12]] I3[[nitrogen N]] O4, also known as T3, is a Thyroid Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a Peptide hormone synthesized and secreted by Thyrotrope cells in the The anterior pituitary (also called the adenohypophysis, from Greek adeno, "gland" hypo, "under" physis, "growth" The thyroid and thyrotropes form a negative feedback loop: TSH production is suppressed when the T4 levels are high, and vice versa. Thyrotropes are cells in the Anterior pituitary which produce Thyroid stimulating hormone. Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a Peptide hormone synthesized and secreted by Thyrotrope cells in the Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the 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). Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a Peptide hormone synthesized and secreted by Thyrotrope cells in the Thyrotropin-releasing hormone ( TRH) also called thyrotropin-releasing factor ( TRF) thyroliberin or protirelin, is a tropic The hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis TSH production is blunted by somatostatin (SRIH), rising levels of glucocorticoids and sex hormones (estrogen and testosterone), and excessively high blood iodide concentration. Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a Peptide hormone synthesized and secreted by Thyrotrope cells in the Somatostatin (also known as growth hormone inhibiting hormone ( GHIH) or somatotropin release-inhibiting factor ( SRIF) is a Peptide hormone Glucocorticoids (GC are a class of Steroid hormones characterised by an ability to bind with the glucocorticoid receptor ( GR) and trigger similar effects Sex steroids, also known as gonadal steroids, are Steroid hormones that interact with Vertebrate Androgen or Estrogen receptors Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, Testosterone is a Steroid hormone from the Androgen group In mammals testosterone is primarily secreted in the testes of males and the Ovaries

Calcitonin

An additional hormone produced by the thyroid contributes to the regulation of blood calcium levels. Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate Calcium levels Parafollicular cells produce calcitonin in response to hypercalcemia. Parafollicular cells (also called C cells) are cells in the Thyroid which produce and secrete Calcitonin. Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the Hypercalcaemia (in American English '''Hypercalcemia''' is an elevated calcium level in the Blood. Calcitonin stimulates movement of calcium into bone, in opposition to the effects of parathyroid hormone (PTH). Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce Parathyroid hormone (PTH, or parathormone, is secreted by the Parathyroid glands as a Polypeptide containing 84 Amino acids. 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 linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the Parathyroid hormone (PTH, or parathormone, 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. A tumor marker is a substance found in the Blood, Urine, or body tissues that can be elevated in Cancer, among other tissue types Thyroid cancer refers to any of four kinds of malignant Tumors of the Thyroid gland papillary, follicular, medullary or Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the It may even be used on biopsy samples from suspicious lesions (e. A biopsy (in Greek: βίος life and όψη look/appearance is a Medical test involving the removal of cells or tissues g. swollen lymph nodes) to establish whether they are metastasis of the original cancer. A Lymph node ( lɪmf noʊd is an organ consisting of many types of cells and is a part of the Lymphatic system. Metastasis ( Greek: displacement μετά=next + στάσις=placement, plural metastases) sometimes abbreviated mets,

Calcitonin can be used therapeutically for the treatment of hypercalcemia or osteoporosis. Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the Hypercalcaemia (in American English '''Hypercalcemia''' is an elevated calcium level in the Blood. Osteoporosis is a Disease of Bone that leads to an increased risk of fracture.

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. Iodine (ˈaɪədaɪn ˈaɪədɪn or /ˈaɪədiːn/ from ιώδης iodes "violet" is a Chemical element that has the symbol I and Atomic Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the A goitre ( BrE) or goiter ( AmE) ( Latin struma) also called a bronchocele, is a swelling in the neck (just below the

Thyroxine is critical to the regulation of metabolism and growth throughout the animal kingdom. Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. 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. Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and Propylthiouracil ( PTU) or 6-N-Propylthiouracil (PROP is a Thioamide drug used to treat Hyperthyroidism by decreasing the amount of A tadpole or polliwog (also pollywog, polliwig, polewig, or polwig) is the wholly aquatic larval stage in the life cycle of Thyroxine, or 353'5'-tetra­iodothyronine (often abbreviated as T4) a form of Thyroid hormones is the major Hormone secreted by the

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. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced This article is about the medical term For the Marxist political concept see Parliamentary 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. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced Newborn screening is the process of testing newborn babies for treatable genetic, endocrinologic, metabolic and hematologic diseases 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 Levothyroxine, also known as L-thyroxine, synthetic T4, or 353'5'-tetraiodo-L-thyronine, is a synthetic form

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. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may 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. Potassium iodide is an Inorganic compound with formula K[[iodide I]] 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. Chernobyl (as transliterated from the Чернобыль) or Chornobyl (as transliterated from Чорнобиль tʃɔrˈnɔbɪlʲ was a city in northern Thyroid cancer refers to any of four kinds of malignant Tumors of the Thyroid gland papillary, follicular, medullary or [3]

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. This article is about the medical term For the Marxist political concept see Parliamentary cretinism. Potassium iodide and Sodium iodide are the most active forms of supplemental iodine.

Diseases

Hyper- and hypofunction

Depending on the prescribed school of thought, affects between 2% and 20% of the population. ^[10]

• Hypothyroidism (underactivity)
  • Hashimoto's thyroiditis / thyroiditis
  • Ord's thyroiditis
  • Postoperative hypothyroidism
  • Postpartum thyroiditis
  • Silent thyroiditis
  • Acute thyroiditis
  • Iatrogenic hypothyroidism
• Hyperthyroidism (overactivity)
  • Thyroid storm
  • Graves-Basedow disease
  • Toxic thyroid nodule
  • Toxic nodular struma (Plummer's disease)
  • Hashitoxicosis
  • Iatrogenic hyperthyroidism
  • De Quervain thyroiditis (inflammation starting as hyperthyroidism, can end as hypothyroidism)

Anatomical problems

• Goitre
  • Endemic goitre
  • Diffuse goitre
  • Multinodular goitre
• Lingual thyroid
• Thyroglossal duct cyst

Tumors

• Thyroid adenoma
• Thyroid cancer
  • Papillary
  • Follicular
  • Medullary
  • Anaplastic
• Lymphomas and metastasis from elsewhere (rare)

Deficiencies

• Cretinism

Medication linked to thyroid disease includes amiodarone, lithium salts, some types of interferon and IL-2. Hypothyroidism is the disease state in humans and animals caused by insufficient production of Thyroid hormone by the Thyroid gland. Hashimoto's thyroiditis or chronic lymphocytic thyroiditis is an Autoimmune disease where the body's own T-cells attack the cells of the Thyroid Thyroiditis is the inflammation of the thyroid gland The thyroid gland is located on the front of the neck below the Laryngeal prominence, and makes hormones that Thyroiditis is the inflammation of the thyroid gland The thyroid gland is located on the front of the neck below the Laryngeal prominence, and makes hormones that 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 Hyperthyroidism is the term for overactive tissue within the Thyroid gland resulting in overproduction and thus an excess of circulating free thyroid hormones Thyroxine Graves' disease is a Thyroid disorder characterized by goiter, Exophthalmos, "orange-peel" skin and Hyperthyroidism. A thyroid adenoma, or solitary thyroid nodule is a Benign tumor of the Thyroid gland Toxic multinodular goitre (also known as toxic nodular goitre, toxic nodular struma) is a form of Hyperthyroidism - where there is excess production of Inflammation ( Latin, inflamatio, to set on fire is the complex biological response of vascular tissues to harmful stimuli such as Pathogens A goitre ( BrE) or goiter ( AmE) ( Latin struma) also called a bronchocele, is a swelling in the neck (just below the A goitre ( BrE) or goiter ( AmE) ( Latin struma) also called a bronchocele, is a swelling in the neck (just below the A goitre ( BrE) or goiter ( AmE) ( Latin struma) also called a bronchocele, is a swelling in the neck (just below the A thyroglossal cyst is a Fibrous cyst that forms from a persistent Thyroglossal duct. A thyroid adenoma, or solitary thyroid nodule is a Benign tumor of the Thyroid gland Thyroid cancer refers to any of four kinds of malignant Tumors of the Thyroid gland papillary, follicular, medullary or Lymphoma a type of Neoplasm that originates in Lymphocytes (a type of White blood cell in the vertebrate Immune system) Metastasis ( Greek: displacement μετά=next + στάσις=placement, plural metastases) sometimes abbreviated mets, This article is about the medical term For the Marxist political concept see Parliamentary cretinism. Amiodarone is an Antiarrhythmic agent (medication used for irregular heart beat used for various types of tachyarrhythmias (fast forms of irregular heart beat both ventricular Lithium in pharmacology refers to use of the Lithium Ion, Li+ as a drug Interferons ( IFN s are natural Proteins produced by the cells of the Immune system of most Vertebrates in response to challenges by foreign agents Interleukin-2 ( IL-2) is an Interleukin, a type of Cytokine Immune system signaling molecule that is instrumental in the body's natural response

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. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced
• Autoantibodies may be detected in various disease states (anti-TG, anti-TPO, TSH receptor stimulating antibodies). An autoantibody is an Antibody (a type of Protein) manufactured by the Immune system that is directed against one or more of the individual's own proteins
• 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. Thyroglobulin (Tg is a 660 kDa dimeric Protein produced by and used entirely within the Thyroid gland Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the
• Very infrequently, TBG and transthyretin levels may be abnormal; these are not routinely tested. Thyroxine-binding globulin (TBG binds Thyroid hormone in circulation 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. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled 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:

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. Nuclear medicine is a branch of Medicine and Medical imaging that uses the nuclear properties of matter in diagnosis and therapy Iodine-123 (123I is a radioactive Isotope of Iodine used in Nuclear medicine imaging including Single photon Nuclear medicine is a branch of Medicine and Medical imaging that uses the nuclear properties of matter in diagnosis and therapy 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.

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 radioiodine 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. A biopsy (in Greek: βίος life and όψη look/appearance is a Medical test involving the removal of cells or tissues Thyroid tissue may be obtained for biopsy by fine needle aspiration or by surgery. "FNA" redirects here For the botanical book series see Flora of North America North of Mexico. Surgery (from the χειρουργική cheirourgikē, via chirurgiae meaning "hand work" is a medical specialty that uses operative manual and instrumental

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 353'5'-tetraiodo-L-thyronine, is a synthetic form Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution but which differ in the three dimensional orientations

Graves' disease may be treated with the thioamide drugs propylthiouracil, carbimazole or methimazole, or rarely with Lugol's solution. Thioamide (rarely thionamide) is a Functional group with the general structure R-CS-NR'R, where R R' and R are organic groups Propylthiouracil ( PTU) or 6-N-Propylthiouracil (PROP is a Thioamide drug used to treat Hyperthyroidism by decreasing the amount of Carbimazole is used to treat Hyperthyroidism. Carbimazole is a Pro-drug as after absorption it is converted to the active form Methimazole. Methimazole (also known as Tapazole) is an antithyroid drug similar in action to Propylthiouracil, and part of the Thioamide Lugol's iodine, also known as Lugol's solution, first made in 1829 is a solution of elemental Iodine and potassium iodide in water named after the French Hyperthyroidism as well as thyroid tumors may be treated with radioactive iodine. Iodine-131 (131I, also called radioiodine, is a Radioisotope of Iodine which has medical and pharmaceutical uses

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

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. Thyroid Nodules are lumps which commonly arise within an otherwise normal thyroid gland A biopsy (in Greek: βίος life and όψη look/appearance is a Medical test involving the removal of cells or tissues A thyroid adenoma, or solitary thyroid nodule is a Benign tumor of the Thyroid gland Hyperthyroidism is the term for overactive tissue within the Thyroid gland resulting in overproduction and thus an excess of circulating free thyroid hormones Thyroxine 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. Graves' disease is a Thyroid disorder characterized by goiter, Exophthalmos, "orange-peel" skin and Hyperthyroidism. A goitre ( BrE) or goiter ( AmE) ( Latin struma) also called a bronchocele, is a swelling in the neck (just below the

A complete thyroidectomy of the entire thyroid, including associated lymph nodes, is the preferred treatment for thyroid cancer. A thyroidectomy involves the surgical removal of all or part of the Thyroid gland. A Lymph node ( lɪmf noʊd is an organ consisting of many types of cells and is a part of the Lymphatic system. Thyroid cancer refers to any of four kinds of malignant Tumors of the Thyroid gland papillary, follicular, medullary or Removal of the bulk of the thyroid gland usually produces hypothyroidism, unless the person takes thyroid hormone replacement. Hypothyroidism is the disease state in humans and animals caused by insufficient production of Thyroid hormone by the Thyroid gland. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced Consequently, individuals who have undergone a total thyroidectomy are typically placed on thyroid hormone replacement for the remainder of their lives. Higher than normal doses are often administered to prevent recurrence.

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. The parathyroid glands are small endocrine Glands in the neck usually located behind the Thyroid gland, which produce Parathyroid hormone. The recurrent (inferior laryngeal nerve is a branch of the vagus nerve (tenth Cranial nerve) that supplies motor function and sensation to the Larynx (voice box 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. Parathyroid hormone (PTH, or parathormone, is secreted by the Parathyroid glands as a Polypeptide containing 84 Amino acids. Removal results in hypoparathyroidism and a need for supplemental calcium and vitamin D each day. In Medicine ( Endocrinology) hypoparathyroidism is decreased function of the Parathyroid glands leading to decreased levels of Parathyroid hormone Vitamin D is a group of fat-soluble Prohormones, the two major forms of which are vitamin D2 (or Ergocalciferol) and vitamin D3 (or In the event the blood supply to any one of the parathyroid glands is endangered through surgery, the parathyroid gland(s) involved may be re-implanted in surrounding muscle tissue. 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. The larynx (plural larynges) colloquially known as the voicebox, is an organ in the Neck of Mammals involved in protection of the The cricothyroid muscle attaches to the anterolateral aspect of the Cricoid and the inferior Cornu and lower Lamina of the Thyroid cartilage 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 vocal folds, also known commonly as vocal cords, are composed of twin infoldings of Mucous membrane stretched horizontally across the Larynx.

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). Salerno is a town in southern Italy, capital of the province of the same name in the region of Campania. 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. Rogerius (before 1140-c 1195 also called Rogerius Salernitanus, Roger Frugard, Roger Frugardi, Roggerio Frugardo, Rüdiger Frutgard 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. ^[11]

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. Anatomy (from the Greek anatomia, from ana separate apart from and temnein, to cut up cut open is a branch of Biology that is the consideration The submandibular duct ( Wharton's duct, submaxillary duct) is about 5 cm ^[12]

Thyroid hormone (or thyroxin) was identified only in the 19th century. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar

Additional images

Position of the Thyroid in Males and Females		Section of the neck at about the level of the sixth cervical vertebra.	Muscles of the neck. Anterior view.
The arch of the aorta, and its branches.	Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries.	Diagram showing common arrangement of thyroid veins.	Sagittal section of nose mouth, pharynx, and larynx.
Muscles of the pharynx, viewed from behind, together with the associated vessels and nerves.	The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.	Section of thyroid gland of sheep. The thyroid is one of the largest Endocrine glands in the body X 160.	The thymus of a full-term fetus, exposed in situ.
Thyoid histology

See also

• Thymus
• Academy of Clinical Thyroidologists

References

External links

• American Thyroid Association (Thyroid Information and professional organization)
• Histology at KUMC epithel-epith03 "Thyroid Gland"
• New Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer from the American Thyroid Association Taskforce. Who Named It? is an English-language dictionary of medical eponyms and the People associated with their identification The University of Kansas (often referred to as KU or just Kansas) is a public research university with campuses located in Lawrence, Kansas City
• Thyroid Disease Manager (free online textbook)
• Thyroid Disease (Nuclear Medicine Information)
• The Thyroid Foundation of America (Education about Thyroid Disease)