Chemistry Of Thyroid Hormones
Thyroid hormones are derivatives of the the amino acid tyrosine bound covalently to iodine. The two principal thyroid hormones are:
As shown in the following diagram, the thyroid hormones are basically two tyrosines linked together with the critical addition of iodine at three or four positions on the aromatic rings. The number and position of the iodines is important. Several other iodinated molecules are generated that have little or no biological activity so called reverse T3 is such an example.
A large majority of the thyroid hormone secreted from the thyroid gland is T4, but T3 is the considerably more active hormone. Although some T3 is also secreted, the bulk of the T3 is derived by deiodination of T4 in peripheral tissues, especially liver and kidney. Deiodination of T4 also yields reverse T3, a molecule with no known metabolic activity.
Thyroid hormones are poorly soluble in water, and more than 99% of the T3 and T4 circulating in blood is bound to carrier proteins. The principle carrier of thyroid hormones is thyroxine-binding globulin, a glycoprotein synthesized in the liver. Two other carriers of import are transthyrein and albumin. Carrier proteins allow maintenance of a stable pool of thyroid hormones from which the active, free hormones are released for uptake by target cells.
Tsh Regulates State Of The Thyroid Gland
TSH is an N-linked glycoprotein of 28 kDa that is synthesized, stored, and released in basophilic cells, called thyrotrophs, of the anterior pituitary. TSH is also called thyrotropin because it is a trophic hormone, derived from the Greek trophos, meaning to nourish. Anterior pituitary trophic hormones increase the size of their target tissue. Like the other pituitary glycoproteins, FSH, LH, and HCG , TSH consists of an and chain that are not covalently linked. The subunits of FSH, LH, HCG, and TSH are identical, whereas the chains confer biological specificity.
TSH binds to specific Gs-coupled receptors on the basolateral membrane of thyroid follicle secretory cells. These receptors link to phosphorylation of cell proteins that regulate thyroid cell metabolism and T3 and T4 synthesis. The short-term effect of TSH on the thyroid is the release of T3 and T4 from already synthesized colloid material. Long-term exposure to TSH increases the size of the thyroid gland by increasing the number of follicular secretory cells and increasing the size of the cells .
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What Do My Parathyroid Glands Do
The parathyroid glands are important in tightly controlling calcium levels in the bloodstream. Because of this, calcium levels are generally very stable. This is important to ensure the nervous system and the bodys muscles can work properly, and also that bones remain strong.
The main target organs where parathyroid hormone exerts its effects are the bones and the kidneys. When calcium levels are low, parathyroid hormone is released by the parathyroid glands into the blood and causes the bones to release calcium and increase levels in the bloodstream. It also causes the kidneys to stop calcium being lost in urine as well as stimulating the kidneys to increase vitamin Dmetabolism .
If someone does not take in enough calcium through their diet or does not have enough vitamin D, circulating calcium levels fall and the parathyroid glands produce more parathyroid hormone. This brings calcium levels in the bloodstream back up to normal.
Another method that parathyroid hormone uses to increase calcium levels in the bloodstream is activation of vitamin D. This occurs in the kidney too the activated vitamin D then increases calcium absorption from the gut.
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Hormones Secreted By The Posterior Pituitary:
Hormones secreted by the Pituitary Gland and their Functions
Hormones Secreted by Pituitary Glands and their Functions:
1. Thyroid stimulating hormone or Thyrotropin: This hormone which is secreted by the anterior lobe of the pituitary.
- TSH acts on the Thyroid gland to release Thyroxine and Triiodothyronine which Regulates Body Metabolism
- Hypothalamus secretes Growth Hormone inhibiting hormone to inhibit the secretion of TSH.
2. Growth hormone : Growth Hormone is also called as or Somatotrophin. Growth hormone is released by the Anterior Pituitary.
- Growth hormone stmulates the Special Liver cells which produce somatomedin-C, which is critical for the growth of all body tissues.
- It assists with the movement of amino acids into tissue cells and the transformation of amino acids into proteins that the body requires.
- It aids in the release of fatty acids from adipose tissue so that they can be used for energy.
- Growth Hormone helps to regulate blood nutrient levels after eating and during periods of fasting.
- When sufficient amounts of Growth Hormone has been released the hypothalamus secretes GHIH which inhibits the further release of growth hormone.
3. Prolactin : It is secreted by Anterior lobe of Pituitary.
- Prolactin hormone stimulates milk production in women following pregnancy.
- Men secrete Prolactin whose function is not known yet.
- Stimulates breast milk production and controls menstrual periods following pregnancy.
How Your Thyroid Works
Your thyroid gland is a small gland, normally weighing less than one ounce, located in the front of the neck. It is made up of two halves, called lobes, that lie along the windpipe and are joined together by a narrow band of thyroid tissue, known as the isthmus.
The thyroid is situated just below your “Adams apple” or larynx. During development the thyroid gland originates in the back of the tongue, but it normally migrates to the front of the neck before birth. Sometimes it fails to migrate properly and is located high in the neck or even in the back of the tongue . This is very rare. At other times it may migrate too far and ends up in the chest .
The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones:thyroxine and triiodothyronine . Thyroid cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism .
The pituitary senses this and responds by decreasing its TSH production. One can imagine the thyroid gland as a furnace and the pituitary gland as the thermostat.
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Which Hormones Does My Thyroid Gland Produce
The thyroid gland produces thyroxine , which is a relatively inactive prohormone. The highly active hormone is triiodothyronine . Collectively, thyroxine and triiodothyronine are referred to as the thyroid hormones. The thyroid gland produces just 20% of the high active T3, but it produces 80% of the prohormone T4. Once secreted by the thyroid, specific enzymes in other tissues like the liver or kidneys may transform T4 in to the active hormone T3.
In addition, there are other hormone-producing cells within the thyroid gland called C-cells. These cells produce calcitonin. Calcitonin plays a role in regulating calcium and phosphate levels in the blood, which is important for your bone health and maintenance.
What Happens In Your Body
Thyroid hormones have an impact on every cell and every organ. Specifically, T3 directly controls the production of various proteins made by your bodys cells. T3 does this by binding to a cells DNA.
Free T4 and free T3 circulating in your blood are available to immediately enter your bodys cells whenever they’re needed, for instance, when you’re cold or when your body is digesting food. Some of the intracellular T4 is converted to T3, and some of the T3 binds to specific T3-receptors in the nucleus of the cell. This bound T3 causes nuclear DNA to stimulate the production of specific proteins.
Among these proteins are various enzymes that, in turn, control the behavior of many important bodily functions mentioned above, such as how quickly your food is digested, your heart rate, body temperature, and how fast calories are burned.
Though thyroid hormones regulate DNA in this way in all cases, different cells in your body have different kinds of T3-nuclear receptors and in different concentrations. As such, the effect of T3 on a cell is quite variable from tissue to tissue and under various circumstances.
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Does The Anterior Pituitary Gland Secrete Oxytocin
Release of oxytocin into the vicinity of the long portal vessels connecting the hypothalamus with the anterior pituitary gland and the presence of short portal vessels connecting the posterior lobe to the anterior pituitary established the potential for the peptide to act in a neuroendocrine fashion controlling the
B Therapeutic Targets For Metabolic Disorders
An improved understanding of the mechanism underlying the actions of TH on lipid metabolism and thermogenesis has led to several useful compounds targeting TR for treatment of metabolic disorders . The thyroid hormone-related thyronamine signaling is a novel pathway to consider for treatment of obesity and metabolic disturbances . The thyronamines are measurable in normal human sera and tissues . Acute T1AM treatment in animals induces hypothermia and reduces metabolism, similar to torpor in hibernating mammals. Although the factors that regulate endogenous T1AM levels are not known, this is a pathway that could potentially be antagonized to raise metabolic rate. T1AM, however, also has the property of rapidly converting an animal from carbohydrate to exclusive fat metabolism, which persists after acute T1AM stimulation . Selective augmentation of this T1AM action is an attractive target for the treatment of metabolic disorders.
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How The Body Adjusts Thyroid Hormones
The body has a complex mechanism for adjusting the level of thyroid hormones. First, the hypothalamus, located just above the pituitary gland in the brain, secretes thyrotropin-releasing hormone, which causes the pituitary gland to produce thyroid-stimulating hormone . Just as the name suggests, TSH stimulates the thyroid gland to produce thyroid hormones. The pituitary gland slows or speeds the release of TSH, depending on whether the levels of thyroid hormones circulating in the blood are getting too high or too low.
What Could Go Wrong With The Thyroid Gland
Normally the thyroid gland produces the exact number of hormones needed to keep your bodys metabolism running and in balance. As described earlier, hormones secreted by the pituitary gland stay constant in your blood circulation, but their levels may increase or decrease when T4 levels in the blood are changing. This hypothalamic-pituitary-thyroid feedback loop keeps the levels of T4 in your blood stable and reacts to small changes immediately.
However, there are several disorders associated with the thyroid gland with most problems concerning the production of thyroid hormones. Either the thyroid gland produces too much hormone or your thyroid doesn’t produce enough hormone , resulting in your body using energy faster or slower than it should.
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Thyroid Hormone Production And Regulation
The thyroid gland produces the hormonesthyroxine, triiodothyronine, and calcitonin. Thyroid hormones thyroxine and triiodothyronine are produced by thyroid folliclar cells. Thyroid cells absorb iodine from certain foods and combine the iodine with tyrosine, an amino acid, to make thyroxine and triiodothyronine . The hormone T4 has four atoms of iodine, while T3 has three atoms of iodine. T4 and T3 regulate metabolism, growth, heart rate, body temperature, and affect protein synthesis. The hormone calcitonin is produced by thyroid parafollicular cells. Calcitonin helps to regulate calcium concentrations by lowering blood calcium levels when the levels are high.
Treatment For Thyroid Gland Disorders
Problems with thyroid hormone levels can be diagnosed with a simple blood test. The presence of antibodies in the blood will confirm Graves or Hashimotos disease. Underactivity is treated by taking thyroxine tablets – a form of hormone replacement. Overactivity is treated with drugs that slow the activity of the thyroid gland. If these do not work, part or all of the thyroid can be removed surgically, or some or all of the active thyroid cells can be killed with radioactive iodine.Nodules and cancers are diagnosed with a variety of different tests, including ultrasound, special x-rays and fine needle biopsies. Hot nodules will generally be removed surgically or destroyed with radioactive iodine. Cold nodules are frequently left alone and simply kept under observation. Cancer is treated by surgically removing the thyroid gland, followed by treatment with radioactive iodine to destroy any cells which may have spread.Taking iodine supplements can be dangerous for patients with Graves disease or hot nodules.
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Thyroid Hormones Are Critically Important To Many Bodily Functions
The thyroid gland is a butterfly-shaped organ located at the base of the neck in front of the trachea . Measuring about two inches wide and weighing 20 to 60 grams, the thyroid gland’s function is to make hormones that are vitally important to the bodys metabolism, growth, and development.
In infants, thyroid hormones are crucial to the development of the brain and the skeletal system. A normal functioning thyroid gland is critical to the normal development of children, and to both the long-term and minute-to-minute well-being of adults.
Thyroid Follicles And Thyroid Function
The thyroid is highly vascular, meaning that it has a wealth of blood vessels. It is composed of follicles that absorb iodine, which is needed to produce thyroid hormones. These follicles store iodine and other substances necessary for thyroid hormone production. Surrounding the follicles are folliclar cells. These cells produce and secrete thyroid hormones into circulation via blood vessels. The thyroid also contains cells known as parafollicular cells. These cells are responsible for the production and secretion of the hormone calcitonin.
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Endocrine Glands And Their Hormones
The hormonal system has various glands that release different hormones.
Hormones are like the bodys communication system. They take messages from one part of the body to tell another part of the body to do something important. The endocrine glands influence reproduction, metabolism, growth and many other functions.
Below is a list of the main glands , some of the hormones they produce and what effects they have on the body.
Hypothalamus: an area in the base of the brain that links the brain to the hormonal system.
- major hormones anti-diuretic hormone , oxytocin, dopamine, corticotrophin releasing hormone, thyrotrophin releasing hormone , gonadotrophin releasing hormone , growth hormone releasing hormone and somatostatin
- influences they hypothalamus links the hormonal and nervous systems. Its hormones keep the body stable. They influence sleep rhythms, alertness, appetite, body weight, thirst, blood pressure, heart rate, sex drive, learning, memory, mood and how the body responds to being sick
Pituitary gland: a kidney bean-shaped gland in the base of the brain.
Which Endocrine Gland Secretes Hormones That Help To Maintain Immune Response
The thymus gland produces several hormones, including: Thymopoietin and thymulin: These hormones are involved in the process where T cells get turned into different types of disease fighters. Thymosin: This hormone boosts the immune systems response. Thymosin also stimulates hormones that control growth.
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When It Doesnt Work Right
Sometimes, the thyroid gland develops a problem. It might start producing too much or too little hormone. It might become enlarged, or it could grow lumps of extra tissue.
More than 12% of people will have some sort of problem with their thyroid during their lifetime. Women are far more likely to have this happen than men.
Common thyroid problems include:
Hypothyroidism. This occurs when your thyroid doesnât make enough hormones. That slows your metabolism. It can make you gain weight and feel sluggish or depressed. Sometimes thatâs caused by a condition called Hashimotoâs disease. This happens when your bodyâs disease-fighting immune system attacks the thyroid.
Hyperthyroidism. If youâre feeling irritable, losing weight, your heart races, and youâre feeling weak, your thyroid might be producing too much hormone. This is often the result of another immune system problem, known as Gravesâ disease, but can be caused by other conditions as well.
Goiters. A goiter happens when your thyroid gland swells up. Sometimes, it makes a noticeable bulge in your neck other times, it can make you cough or make your voice sound hoarse. A goiter can be caused by other thyroid conditions or by a lack of iodine, an element your thyroid needs to work properly. Most Americans get plenty of iodine because itâs now added to table salt in the United States.
Other Thyroid Gland Disorders
Other disorders of the thyroid gland include:
- Nodules – lumps in the thyroid. Some are groups of uncontrollably overactive thyroid cells. These are called hot nodules and cause hyperthyroidism. Other nodules are cold. These are generally harmless, but about 20 per cent will be cancerous.
- Cancer – thyroid cancer is uncommon and is readily treatable, especially if detected early.
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A Thyroid Hormone Receptor Nuclear Receptor Partners And Response Coregulators
1. Thyroid receptor isoforms
TH action is exerted primarily via the nuclear TR, a member of the superfamily of hormone-responsive nuclear transcription factors that share a similar structure and mechanism of action . The structure of the nuclear receptors, such as TR, includes a zinc finger motif DNA binding domain and a COOH-terminal domain that mediates ligand interactions as well as binding of coactivators and corepressors . The function of the amino terminus varies among nuclear receptors, but for TR has minimal functional significance. There are two primary isoforms of TR, and , which are differentially expressed developmentally and in adult tissues . Both TR and undergo posttranslational modification by sumoylation, which is essential for positive and negative gene regulation by TH, including genes important for metabolic regulation . Sumoylation of PPAR is essential for adipogenesis in a SUMO1 gene knockout mouse model . TR sumoylation may similarly impact metabolic genes directly regulated by TR and genes regulated by TR crosstalk with other nuclear receptors.
2. Retinoid X receptor
3. Nuclear receptor coregulators
4. Resistance to TH