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Updated visitor guidelines. Top of the page. Thyroid Hormone Production and Function. Topic Overview The thyroid gland uses iodine from food to make two thyroid hormones: triiodothyronine T3 and thyroxine T4. When the hypothalamus and pituitary are working normally, they sense when: Thyroid hormone levels are low, so they secrete more TRH and TSH, which stimulates the thyroid to make more hormones. Thyroid hormone levels are too high, so they secrete less TRH and TSH, which reduces hormone production by the thyroid.
The pituitary gland produces and sends out a hormone called thyroid-stimulating hormone TSH. TSH then tells the thyroid gland how much hormones to produce and secrete. There is a third actor involved in this communication. The pituitary gland responds either directly to the thyroid hormones in the blood, but it also responds to signals from the hypothalamus , which sits above the pituitary gland as part of your brain. The hypothalamus releases its own hormone thyrotropin-releasing hormone TRH.
The thyroid gland produces thyroxine referred to as T4 , which is a relatively inactive prohormone. The highly active hormone is triiodothyronine referred to as T3. Collectively, thyroxine and triiodothyronine are referred to as the thyroid hormones. 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.
As described earlier, hormones secreted by the pituitary gland TSH 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 called hyperthyroidism or your thyroid doesn't produce enough hormone called hypothyroidism , resulting in your body using energy faster or slower than it should.
Symptoms for hypothyroidism is the contrary of hyperthyroidism such as weight gain, slower heart rate, fatigue, more frequent and stronger menstrual periods, forgetfulness, dry skin and hair, hoarse voice and intolerance to cold. In addition, hypothyroidism is often accompanied by an enlargement of the thyroid gland known as goitre.
On a worldwide scale, approximately million people have some form of thyroid disease. People of all ages and races can get thyroid disease. However, women are 5 to 8 times more likely than men to get problems with their thyroid function. 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.
Your thyroid makes 2 main hormones — triiodothyronine T3 and thyroxine T4. This hormone, secreted by a small population of cells known as C cells, is involved in regulating the level of calcium and phosphate in your blood.
The main thyroid hormones are secreted directly into the bloodstream and go to all parts of your body. Most T4 is converted to T3 the active form of the hormone in your organs and tissues. The amount of hormones your thyroid makes is usually tightly regulated. A part of your brain called the hypothalamus signals your pituitary gland an important gland in your brain to produce a hormone called thyroid stimulating hormone TSH.
TSH then signals your thyroid to make T3 and T4. The level of thyroid hormones in your body then feeds back to the hypothalamus and the pituitary, which in turn adjust the release of TSH. Thyroid dysfunction is when too much or not enough thyroid hormones are made.
It can be caused by:. While an inadequate intake of iodine is the most common cause of thyroid disease worldwide, autoimmune problems where your immune system makes antibodies that attack the thyroid gland are the most common cause of thyroid problems in Australia. Sometimes thyroid problems start during or after pregnancy. Hyperthyroidism happens when there is an overproduction of thyroid hormones.
It can result in symptoms such as:. It can cause swelling of the thyroid goitre and thyroid eye disease.
It usually affects people aged between 20 and 60 years of age, and is much more common in women than in men.
Hypothyroidism is when you have an underactive thyroid. Symptoms usually develop gradually, sometimes over several years, and can include:. Damage to the thyroid from radiation treatment used to treat head or neck cancers or certain medicines e. And sometimes treatment for an overactive thyroid can unfortunately end up causing hypothyroidism.
If you have a family history of thyroid problems or have an autoimmune disease you are also at increased risk. Untreated thyroid disorders can lead to other problems, such as heart disease, high cholesterol, high blood pressure and osteoporosis.
If you have noticed any swelling in the neck, or have noticed symptoms of an overactive or underactive thyroid, talk to your doctor. If your GP general practitioner suspects you have a thyroid problem, they will ask about your symptoms and do a physical examination, including examining your neck.
Both hyperthyroidism and hypothyroidism can be associated with generalised swelling of the thyroid, known as goitre. Thyroid nodules non-cancerous lumps and thyroid cancer may show up as firm, usually painless, lumps in the thyroid. Simple blood tests can be done to assess your thyroid function and help work out the cause of your thyroid problem.
Scans of your thyroid gland may sometimes also be needed to diagnose thyroid disease. Your doctor may refer you to an endocrinologist doctor who specialises in treating hormonal conditions such as thyroid disease or a thyroid surgeon for further tests and treatment. Blood tests can be done to measure the levels of the different thyroid hormones — thyroid stimulating hormone TSH , free T4 thyroxine and free T3 triiodothyronine.
By measuring the free hormones, the results are not affected by changes in the levels of thyroid hormone-binding proteins. Thyroid stimulating hormone TSH is the best initial test of thyroid function.
If the TSH is abnormal, free T4 is then usually measured. These people often do not have any obvious symptoms. Subclinical hypothyroidism is more common than overt hypothyroidism. Blood tests for thyroid antibodies can help work out the cause of your thyroid problem. Thyroid nuclear medicine scans can help work out the cause of hyperthyroidism overactive thyroid. Radionuclide thyroid scanning can show whether the whole thyroid or a nodule or nodules within the thyroid is overactive.
Scans can show the structure and the function of your thyroid gland. An ultrasound scan may be needed if there is swelling of the thyroid or a lump. Ultrasound scans can show whether a lump is cystic fluid-filled or solid.
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