The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thyroid is located at the front of the neck, below the Adam's apple. Microscopically, the functional unit of the thyroid gland is the spherical thyroid follicle, lined with follicular cells (thyrocytes), and occasional parafollicular cells that surround a lumen containing colloid. The thyroid gland secretes three hormones: the two thyroid hormones – triiodothyronine (T3) and thyroxine (T4) – and a peptide hormone, calcitonin. The thyroid hormones influence the metabolic rate and protein synthesis, and in children, growth and development. Calcitonin plays a role in calcium homeostasis. Secretion of the two thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is secreted from the anterior pituitary gland. TSH is regulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus.
Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body. It is a glycoprotein hormone produced by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid.
Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
Thyroid follicular cells are the major cell type in the thyroid gland, and are responsible for the production and secretion of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). They form the single layer of cuboidal epithelium that makes up the outer structure of the almost spherical thyroid follicle.
Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis and Hashimoto's disease, is an autoimmune disease in which the thyroid gland is gradually destroyed. Early on, symptoms may not be noticed. Over time, the thyroid may enlarge, forming a painless goiter. Some people eventually develop hypothyroidism with accompanying weight gain, fatigue, constipation, depression, hair loss, and general pains. After many years the thyroid typically shrinks in size. Potential complications include thyroid lymphoma.
Thyroid peroxidase, also called thyroperoxidase (TPO) or iodide peroxidase, is an enzyme expressed mainly in the thyroid where it is secreted into colloid. Thyroid peroxidase oxidizes iodide ions to form iodine atoms for addition onto tyrosine residues on thyroglobulin for the production of thyroxine (T4) or triiodothyronine (T3), the thyroid hormones. In humans, thyroperoxidase is encoded by the TPO gene.
Thyroid disease is a medical condition that affects the function of the thyroid gland. The thyroid gland is located at the front of the neck and produces thyroid hormones that travel through the blood to help regulate many other organs, meaning that it is an endocrine organ. These hormones normally act in the body to regulate energy use, infant development, and childhood development.
Papillary thyroid cancer or papillary thyroid carcinoma is the most common type of thyroid cancer, representing 75 percent to 85 percent of all thyroid cancer cases. It occurs more frequently in women and presents in the 20–55 year age group. It is also the predominant cancer type in children with thyroid cancer, and in patients with thyroid cancer who have had previous radiation to the head and neck. It is often well-differentiated, slow-growing, and localized, although it can metastasize.
Midkine, also known as neurite growth-promoting factor 2 (NEGF2), is a protein that in humans is encoded by the MDK gene.
The sodium/iodide cotransporter, also known as the sodium/iodide symporter (NIS), is a protein that in humans is encoded by the SLC5A5 gene. It is a transmembrane glycoprotein with a molecular weight of 87 kDa and 13 transmembrane domains, which transports two sodium cations (Na+) for each iodide anion (I−) into the cell. NIS mediated uptake of iodide into follicular cells of the thyroid gland is the first step in the synthesis of thyroid hormone.
The G protein-coupled bile acid receptor 1 (GPBAR1) also known G-protein coupled receptor 19 (GPCR19), membrane-type receptor for bile acids (M-BAR) or TGR5 as is a protein that in humans is encoded by the GPBAR1 gene.
Paired box gene 8, also known as PAX8, is a protein which in humans is encoded by the PAX8 gene.
S100 calcium-binding protein A6 (S100A6) is a protein that in humans is encoded by the S100A6 gene.
Dual oxidase 2, also known as DUOX2 or ThOX2, is an enzyme that in humans is encoded by the DUOX2 gene. Dual oxidase is an enzyme that was first identified in the mammalian thyroid gland. In humans, two isoforms are found; hDUOX1 and hDUOX2. The protein location is not exclusive to thyroid tissue; hDUOX1 is prominent in airway epithelial cells and hDUOX2 in the salivary glands and gastrointestinal tract.
Follicular thyroid cancer accounts for 15% of thyroid cancer and occurs more commonly in women over 50 years of age. Thyroglobulin (Tg) can be used as a tumor marker for well-differentiated follicular thyroid cancer. Thyroid follicular cells are the thyroid cells responsible for the production and secretion of thyroid hormones.
Thyroid hormones are two hormones produced and released by the thyroid gland, namely triiodothyronine (T3) and thyroxine (T4). They are tyrosine-based hormones that are primarily responsible for regulation of metabolism. T3 and T4 are partially composed of iodine. A deficiency of iodine leads to decreased production of T3 and T4, enlarges the thyroid tissue and will cause the disease known as simple goitre.
Autoimmune thyroiditis, is a chronic disease in which the body interprets the thyroid glands and its hormone products T3, T4 and TSH as threats, therefore producing special antibodies that target the thyroid's cells, thereby destroying it. It may present with hypothyroidism or hyperthyroidism and with or without a goiter.
Iodotyrosine deiodinase, also known as iodotyrosine dehalogenase 1, is a type of deiodinase enzyme that scavenges iodide by removing it from iodinated tyrosine residues in the thyroid gland. These iodinated tyrosines are produced during thyroid hormone biosynthesis. The iodide that is scavenged by iodotyrosine deiodinase is necessary to again synthesize the thyroid hormones. After synthesis, the thyroid hormones circulate through the body to regulate metabolic rate, protein expression, and body temperature. Iodotyrosine deiodinase is thus necessary to keep levels of both iodide and thyroid hormones in balance.
Antithyroid autoantibodies (or simply antithyroid antibodies) are autoantibodies targeted against one or more components on the thyroid. The most clinically relevant anti-thyroid autoantibodies are anti-thyroid peroxidase antibodies (anti-TPO antibodies, TPOAb), thyrotropin receptor antibodies (TRAb) and thyroglobulin antibodies (TgAb). TRAb's are subdivided into activating, blocking and neutral antibodies, depending on their effect on the TSH receptor. Anti-sodium/iodide (Anti–Na+/I−) symporter antibodies are a more recent discovery and their clinical relevance is still unknown. Graves' disease and Hashimoto's thyroiditis are commonly associated with the presence of anti-thyroid autoantibodies. Although there is overlap, anti-TPO antibodies are most commonly associated with Hashimoto's thyroiditis and activating TRAb's are most commonly associated with Graves' disease. Thyroid microsomal antibodies were a group of anti-thyroid antibodies; they were renamed after the identification of their target antigen (TPO).
Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is an indolent thyroid tumor that was previously classified as an encapsulated follicular variant of papillary thyroid carcinoma, necessitating a new classification as it was recognized that encapsulated tumors without invasion have an indolent behavior, and may be over-treated if classified as a type of cancer.
