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What System Is The Thyroid Gland In

Thyroid Hormones T3 And T4

Thyroid Gland and Thyroid Hormone | Endocrine System | Step 1 Simplified

These hormones keep your body functioning at the right speed.

If your thyroid gland does not make enough hormones, your bodys cells work slower than normal. You usually feel tired and put on weight more easily. This is called hypothyroidism, or an underactive thyroid.

If your thyroid gland makes too many hormones, your bodys cells work faster than normal. This is called hyperthyroidism, or an overactive thyroid. You usually lose weight, feel hungrier than normal, and feel shaky and anxious. Your heartbeat may be faster than normal or irregular.

A part of your brain called the hypothalamus senses if the levels of T3 and T4 in your blood are too low. If they are, it sends thyroid-releasing hormones into your blood. The rising level of TRH makes another gland in the brain release thyroid-stimulating hormone . TSH then stimulates the thyroid gland to produce more T3 and T4. If your brain senses that the levels of T3 and T4 are too high, it sends messages to lower the amount of TSH.

Most people with thyroid cancer have normal levels of T3 and T4.

The thyroid gland needs a regular supply of iodine to produce thyroid hormones. We get iodine from our diet. It is mainly found in fish, seafood and dairy products. Some types of salt also contain iodine, but they are not commonly used in the UK.

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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.

Recap: What’s The Difference Between The Thyroid And Parathyroids

Weve talked about how the thyroid produces hormones that increase the base metabolic rate of cells in the body by attaching to their mitochondria and giving them a boost. The thyroid also produces calcitonin, which helps maintain calcium homeostasis.

While calcium regulation is a secondary function for the thyroid, its the parathyroids primary concern. Its their job to make sure theres enough calcium in the body for nerves and muscles to function.

Its important to note that while the parathyroids secrete PTH when calcium levels are low, the thyroid secretes calcitonin when calcium levels are too high.

And thats all for nowwe hope youve enjoyed this introduction to a few of your friendly neighborhood endocrine glands! You can meet a few more, such as the pineal gland, adrenal glands, and pancreas, in this blog post about the endocrine system. And if youd like to learn more about the hypothalamus and pituitary gland in particular, check out this blog post.

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How Does The Thyroid Work

The main job of the thyroid gland is to produce hormones T4 and T3. To do this the thyroid gland has to take a form of iodine from the bloodstream into the thyroid gland itself. This substance then undergoes a number of different chemical reactions which result in the production of T3 and T4.

The activity of the thyroid is controlled by hormones produced by two parts of the brain the hypothalamus and the pituitary gland. The hypothalamus receives input from the body about the state of many different bodily functions. When the hypothalamus senses that levels of T3 and T4 are low, or that the bodys metabolic rate is low, it releases a hormone called thyrotropin-releasing hormone . TRH travels to the pituitary gland via the connecting blood vessels. TRH stimulates the pituitary gland to release thyroid-stimulating hormone .

TSH is released from the pituitary gland into the bloodstream and travels to the thyroid gland. Here, TSH causes cells within the thyroid gland to make more T3 and T4. T3 and T4 are then released into the bloodstream where they increase metabolic activity in the bodys cells. High levels of T3 stop the hypothalamus and pituitary gland from secreting more of their hormones. In turn this stops the thyroid gland producing T3 and T4. This system ensures that T3 and T4 should only be made when their levels are too low.

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How The Hypothalamus And Pituitary Gland Regulate Thyroid Hormone Release

Chapter 22: Endocrine System  Human Biology

This just wouldnt be a discussion about the endocrine system if it didnt include the masterminds of hormone release: the hypothalamus and the pituitary gland, two structures in the brain.

Image from Human Anatomy Atlas.

When levels of thyroid hormones in the bloodstream become low, the hypothalamus is the first to spring into action, producing a hormone called TRH . This signals the the hypothalamus good buddy the pituitary gland to release TSH .

Thyroid-related hormones released by the hypothalamus and anterior pituitary gland.

TSH is the messenger from the brain that tells the thyroid to make and release more T4 and T3. Once the levels of thyroid hormones in the blood have increased sufficiently, the pituitary gland stops releasing TSH.

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Thyroid Hormones: T4 And T3

There are two main thyroid hormones produced by the follicles: thyroxine , which contains four iodide ions and is represented by the structural diagram below , and triiodothyronine , which contains three iodide ions. T3 is much more powerful than T4, but T4 makes up about 90 per cent of circulating thyroid hormone, and T3 makes up only about ten per cent. However, most of the T4 is converted to T3 by target tissues.

Figure 9.5.3 This structural model represents a single molecule of thyroxine . The Is represent the four iodide ions it contains. The rings consist mainly of carbon atoms.

Like steroid hormones, T3 and T4 cross cell membranes everywhere in the body and bind to intracellular receptors to regulate gene expression. Unlike steroid hormones, however, thyroid hormones can cross cell membranes only with the help of special transporter proteins. Once inside the nucleus of cells, T3 and T4 turn on genes that control protein synthesis. Thyroid hormones increase the rate of metabolism in cells, allowing them to absorb more carbohydrates, use more energy, and produce more heat. Thyroid hormones also increase the rate and force of the heartbeat. In addition, they increase the sensitivity of cells to fight-or-flight hormones .

Figure 9.5.4 The thyroid system is a negative feedback loop that includes the hypothalamus, pituitary gland, and thyroid gland. As this diagram shows, thyroid hormones increase the effect of catecholamines such as adrenaline, a fight-or-flight hormone.

What Common Symptoms Can Happen With Thyroid Disease

There are a variety of symptoms you could experience if you have a thyroid disease. Unfortunately, symptoms of a thyroid condition are often very similar to the signs of other medical conditions and stages of life. This can make it difficult to know if your symptoms are related to a thyroid issue or something else entirely.

For the most part, the symptoms of thyroid disease can be divided into two groups those related to having too much thyroid hormone and those related to having too little thyroid hormone .

Symptoms of an overactive thyroid can include:

  • Experiencing anxiety, irritability and nervousness.
  • Having trouble sleeping.
  • Experiencing an intolerance to cold temperatures.

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What Causes Thyroid Disease

There are various different factors causing hyper- and hypothyroidism.

The following conditions cause hypothyroidism:

Thyroiditis is an inflammation of the thyroid gland. This can lower the number of hormones produced.

A special form of thyroiditis is Hashimoto’s thyroiditis. This is a genetic disorder caused by diseases of the immune system and can be passed from one generation to the other. In addition, thyroiditis can occur in women after giving birth also referred to as postpartum thyroiditis. It is usually a temporary condition and occurs only in 5-9% of woman giving birth.

Nutrition also impacts your thyroid functions. Iodine deficiency can cause hypothyroidism. This is a worldwide problem affecting approximately 100 million people. As mentioned earlier, iodine is used by the thyroid gland to produce hormones.

The following conditions cause hyperthyroidism:

Graves’ disease is a condition where the entire thyroid gland might be overactive and produce too much hormone. Your thyroid gland might be enlarged. This problem is also called diffuse toxic goitre.

Thyroiditis can also cause the opposite and trigger the release of hormones that were stored in the thyroid gland. This uncontrolled release of thyroid hormones causes hyperthyroidism for a few weeks or months. It may occur in women after childbirth.

Hormone Imbalances: Overactive And Underactive Thyroid Gland

Thyroid Gland, Hormones and Thyroid Problems, Animation

An overactive thyroid occurs if the thyroid gland makes too many hormones. An underactive thyroid is where the gland doesnt make enough hormones. Both of these imbalances can lead to a great number of symptoms.

The thyroid gland may grow in size too. Sometimes the whole thyroid gland becomes enlarged , and sometimes individual lumps called nodules grow in the gland . A special examination, known as thyroid scintigraphy, can be used to see whether these nodules are producing abnormal amounts of hormones. If they make more hormones than the rest of the thyroid tissue, they are called hot nodules. If they make less, they are called cold nodules.

In most cases, an enlarged thyroid or nodules arent caused by anything serious. They are only rarely cancer. But its still important to see a doctor if you notice any changes in your thyroid gland.

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Hypothyroidism Diagnosis And Treatment

Your doctor will perform blood tests to measure your TSH and thyroid hormone levels. A high TSH level and low thyroxine level could mean that your thyroid is underactive. These levels could also indicate that your pituitary gland is releasing more TSH to try to stimulate the thyroid gland to make its hormone.

The main treatment for hypothyroidism is to take thyroid hormone pills. Its important to get the dose right, because taking too much thyroid hormone can cause symptoms of hyperthyroidism.

Feature: Myth Vs Reality

Thyroid disorders are relatively common, affecting as many as 20 million people in the United States. According to recent studies, one in ten Canadians have some type of thyroid condition and up to 50 per cent may be undiagnosed! Because thyroid disorders are common, there are also many common myths about them.

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Overview Of The Thyroid Gland

, MD, MS, David Geffen School of Medicine at UCLA

The thyroid is a small gland, measuring about 2 inches across, that lies just under the skin below the Adams apple in the neck. The two halves of the gland are connected in the middle , giving the thyroid gland the shape of a bow tie. Normally, the thyroid gland cannot be seen and can barely be felt. If it becomes enlarged, doctors can feel it easily, and a prominent bulge may appear below or to the sides of the Adams apple.

The thyroid gland secretes thyroid hormones, which control the speed at which the bodys chemical functions proceed . Thyroid hormones influence the metabolic rate in two ways:

Thyroid hormones affect many vital body functions, such as the heart rate, the rate at which calories are burned, skin maintenance, growth, heat production, fertility, and digestion.

When It Doesnt Work Right

All About the Thyroid: Hypothyroid

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.

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What Role Does The Thyroid Gland Play In The Human Body

The thyroid gland plays a major role in the human bodys everyday functions by secreting hormones that control metabolism, according to Harvard Medical School. Because the thyroid gland produces the substances that influence and regulate the bodys metabolism, it functions in a manner similar to the conductor of an orchestra. Metabolism determines the rate at which cells are produced, nutrients are absorbed and energy is used, which affects every organ and system in the body.

The pituitary gland monitors the levels of hormones in the bloodstream and sends an activation signal to the thyroid gland when levels of the hormones called T3 and T4 are low. These are the metabolism-regulating hormones produced by the thyroid gland, and when it receives the production signal from the pituitary gland, T3 and T4 are produced and secreted.

When the thyroid gland is unable to produce the called-for amounts of T3 and T4, which results in a slowing down of the bodys metabolism, the condition is referred to as hypothyroidism. Some of the symptoms resulting from hypothyroidism are either similar to those of clinical depression or they are capable of causing depression. There are clinicians who believe that some people who are taking anti-depressant medications should instead be examined and tested for hypothyroidism, as reported in the Harvard Medical School newsletter.

Growth Hormone / Insulin

Somatopause is a term used to describe the change in GH/IGF-I axis, which involves a decrease in production and sensitivity to GH and IGF-I. Typically, GH secretion declines 14% with each decade of life. In the developing human body, GH from the anterior pituitary gland stimulates production and release of IGF-I by the liver, which is then transported in the blood to stimulate growth of muscle and bone.

With aging, a decrease in the amount of circulating GH and consequently IGF-I results in weaker bones with a low bone mineral density . In addition to lower circulating amounts of IGF-I, the responsiveness of bone to this protein has been shown to decrease in animal models. This can be attributed to a decrease in IGF-I signaling pathways with advanced cell age. Binding of IGF-I to its receptors normally initiates signaling cascades involving phosphorylation of extracellular signal related kinase and cyclin-dependent kinase . These two pathways combine to promote osteoblast proliferation and survival.

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Hashimotos Diagnosis And Treatment

Testing the level of TSH is often the first step when screening for any type of thyroid disorder. Your doctor might order a blood test to check for increased levels of TSH as well as low levels of thyroid hormone if youre experiencing some of the above symptoms. Hashimotos thyroiditis is an autoimmune disorder, so the blood test would also show abnormal antibodies that might be attacking the thyroid.

Theres no known cure for Hashimotos thyroiditis. Hormone-replacing medication is often used to raise thyroid hormone levels or lower TSH levels. It can also help relieve the symptoms of the disease. Surgery might be necessary to remove part or all of the thyroid gland in rare advanced cases of Hashimotos. The disease is usually detected at an early stage and remains stable for years because it progresses slowly.

How Can I Promote The Health Of The Thyroid Gland

video 7 endocrine system thyroid, parathyroid, pineal gland

Iodine is most essential to maintain a healthy thyroid. Iodine is the critical ingredient for the production of thyroid hormones. We dont need a lot of iodine, it is said that one teaspoon of iodine is enough for a lifetime. Nonetheless, the daily and constant supply of this micronutrient is important. Too much iodine at once is counter-productive and causes your thyroid to produce less hormones. The best way to get your daily dose of iodine is through eating healthy foods like seafood and dairy products. In addition, iodized salt is a good source and you can use it to season your food. Nowadays, iodine is added to salt to combat goitres .

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Biochemistry Of Thyroid Hormone

Thyroxine and triiodothyronine contain iodine and are formed from thyronines, which are composed of two molecules of the amino acidtyrosine. Thyroxine contains four iodine atoms, and triiodothyronine contains three iodine atoms. Because each molecule of tyrosine binds one or two iodine atoms, two tyrosines are used to synthesize both thyroxine and triiodothyronine. These two hormones are the only biologically active substances that contain iodine, and they cannot be produced in the absence of iodine. The process leading to the eventual synthesis of thyroxine and triiodothyronine begins in the thyroid follicular cells, which concentrate iodine from the serum. The iodine is then oxidized and attached to tyrosine residues within thyroglobulin molecules. The iodinated tyrosine residues are then rearranged to form thyroxine and triiodothyronine. Therefore, thyroglobulin serves not only as the structure within which thyroxine and triiodothyronine are synthesized but also as the storage form of the two hormones.


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