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What system is the thyroid part of: Thyroid gland | You and Your Hormones from the Society for Endocrinology

The thyroid gland

What is the thyroid gland?

The thyroid gland is a key part of the human endocrine system and works together with your nervous and immune systems to regulate your body’s metabolism.

Metabolism refers to all of the processes that go on inside your body, for example, the process of turning food into energy.

The thyroid gland regulates metabolism by producing and secreting hormones into your bloodstream.

Terms explained

Autoimmune disorder – a condition where your own antibodies attack your body.

Where is the thyroid gland?

The thyroid gland is located in the lower front part of your throat, just below your Adam’s apple. It consists of 2 lobes on either side of your windpipe.

What does the thyroid gland do?

Your thyroid produces 2 important hormones:

  • Thyroxine, known as T4
  • tri-iodothyronine, known as T3.

Thyroid hormones affect your:

  • body temperature and circulation
  • appetite
  • energy levels
  • growth and bone development
  • muscle tone and suppleness
  • heart rate
  • blood sugar levels
  • central nervous system and bowel function
  • cholesterol levels
  • fat, carbohydrate and protein metabolism.

Thyroid hormones and metabolism

Your thyroid controls the chemical metabolic processes constantly taking place inside your body. This process of metabolism is how your body gets the energy it needs to survive and has a vital function.

Your body needs iodine to make thyroid hormones. Most people get suitable amounts of iodine from their diet as it is found in most food, especially seafood. Small amounts of iodine are found in vegetables grown in soils containing iodine.

If your thyroid cannot produce a sufficient amount of hormones you are vulnerable to a range of serious health conditions.

The higher the T3 and T4 iodine count that circulates in your blood the faster your metabolism is. If you have less T3 and T4, your metabolism levels drop.

If your thyroid becomes overactive (hyperthyroidism), or underactive (hypothyroidism) it is not performing normally and starts to produce abnormal chemical reactions in your body leading to:

  • disruption of your entire metabolic system
  • unusually high or low levels of hormones or enzymes
  • malfunctioning hormones or enzymes
  • a build-up of toxic substances in your body
  • diseases and serious health conditions.

Your pituitary and thyroid glands

The pituitary is an endocrine gland located at the base of your brain that controls your endocrine system, including your thyroid. The pituitary affects the thyroid by producing a hormone called thyroid stimulating hormone (TSH).

TSH causes cells within your thyroid to make more T3 and T4 hormone.

If there is too much T4 in your bloodstream your pituitary produces less TSH, which causes your thyroid activity to slow. If there is not enough T4 hormone the pituitary increases the amount of TSH to help speed up your metabolism.


A goitre is when your thyroid gland becomes significantly swollen and enlarged – this can happen if your diet is low in iodine.

If you are iodine deficient your pituitary gland may try to compensate by overstimulating your thyroid to produce more thyroid hormone. When this happens your thyroid grows larger and larger.

The presence of goitre in your neck suggests your thyroid is not functioning properly or you are iodine deficient.

Other thyroid gland disorders

Several disorders are associated with the thyroid gland:

  • Graves’ disease
  • Hashimoto’s disease
  • thyroid cancer
  • thyroid nodules
  • congenital thyroid disease
  • iodine deficiency disorder.

Hyperthyroidism – overactive thyroid

Hyperthyroidism is a condition where your thyroid is overactive and releases too many T4 and T3 hormones into your bloodstream, creating a hormonal imbalance and causing your metabolism to speed up.

The most common cause of hyperthyroidism is an autoimmune condition called Graves’ disease.

Learn more about hyperthyroidism, including Graves’ disease and the symptoms and treatment of an overactive thyroid.

Hypothyroidism – underactive thyroid

Hypothyroidism is a condition where your thyroid is underactive and releases too little T4 and T3 hormones into your bloodstream.

This causes your metabolism to slow down too much and reduces the thyroid’s ability to make hormones.

The most common cause of hypothyroidism is an autoimmune condition called Hashimoto’s disease.

Learn more about hypothyroidism, including Hashimoto’s disease and the symptoms and treatment of an underactive thyroid.

Where to get help

  • See your doctor
  • See your endocrinologist
  • Visit a GP after hours
  • Ring healthdirect Australia on 1800 022 222.


  • People with a family history of thyroid conditions have a higher risk of also getting thyroid and other autoimmune conditions.
  • An overactive thyroid (hyperthyroidism) releases too much T4 and T3 into your blood stream and causes your metabolism to speed up.
  • An underactive thyroid (hypothyroidism) does not release enough T4 and T3 into your blood stream and causes your metabolism to slow down too much.
  • Thyroid conditions can be treated and have a good prognosis.
  • Thyroid conditions affect more women than men.


Diabetes and Endocrine Health Network

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

See also

  • Hyperthyroidism (overactive thyroid)

  • Hypothyroidism (underactive thyroid)

  • Your family health history

  • Genetic conditions

  • Genetic testing

Thyroid gland | You and Your Hormones from the Society for Endocrinology

Where is my thyroid gland?

The thyroid gland is located at the front of the neck just below the Adam’s apple (larynx). It is butterfly-shaped and consists of two lobes located either side of the windpipe (trachea). A normal thyroid gland is not usually outwardly visible or able to be felt if finger pressure is applied to the neck.

click to enlarge

Diagram showing the location of the thyroid gland in the neck. It has two lobes and sits in front of the windpipe (trachea). The voice box (larynx) sits just above the thyroid. Image created using Biorender.

What does the thyroid gland do?

The thyroid gland produces hormones that regulate the body’s metabolic rate, growth and development. It plays a role in controlling heart, muscle and digestive function, brain development and bone maintenance. Its correct functioning depends on a good supply of iodine from the diet. Cells producing thyroid hormones are very specialised in extracting and absorbing iodine from the blood and incorporating it into the thyroid hormones.

Who tells the thyroid to produce and release hormones? 

The signal comes from a small gland located at the bottom of our brain called the pituitary gland. The pituitary gland produces and sends out a hormone called thyroid-stimulating hormone (TSH). TSH then tells the thyroid gland how much hormone to produce and secrete. TSH levels in your blood are rising and falling depending on your body’s needs, to produce more or less thyroid hormones.

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). TRH in turn stimulates the release of TSH in the pituitary, which then signals to the thyroid gland.

This whole network is also referred to as the hypothalamic-pituitary-thyroid axis (HPT) and it adapts to metabolic changes and your body’s needs.

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Diagram showing the hypothalamic-pituitary-thyroid axis (HPT). The highlighted areas show the hypothalamus and the anterior pituitary. Image created using Biorender

Which hormones does my thyroid gland produce?

The thyroid gland produces thyroxine (referred to as T4), which is a relatively inactive prohormone, and the highly active hormone called triiodothyronine (referred to as T3). Collectively, thyroxine and triiodothyronine are referred to as the thyroid hormones. The thyroid gland produces just 20% of the highly active T3, and it mainly produces the prohormone T4, which constitutes about 80% of the secreted thyroid hormones. Once secreted by the thyroid, specific enzymes in other tissues like the liver or kidneys convert T4 into the active hormone T3 (which accounts for most of the T3 in the body).

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 maintain healthy bones.

What could go wrong with the thyroid gland?

Normally the thyroid gland produces the exact number of hormones needed to keep your body’s metabolism running and in balance. As described earlier, TSH secreted by the pituitary gland remains at a constant level in your blood circulation, but the level increases when the T4 levels fall and decrease when T4 levels in the blood rise. 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), resulting in your body using energy more quickly than it should; or your thyroid doesn’t produce enough hormone (called hypothyroidism), resulting in your body using energy more slowly than it should. Rarely cancer of the thyroid gland may develop.

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Diagram showing the effects of the thyroid hormone on various organs. Image created using Biorender.

What are typical symptoms of hyper- and hypothyroidism?

Typical symptoms for hyperthyroidism are weight loss, fast (and sometimes irregular) heart rate, irritability/nervousness, muscle weakness and tremors, changes in menstrual periods, sleep problems, eye problems and heat sensitivity.

Symptoms for hypothyroidism include weight gain, slower heart rate, fatigue, menstrual period abnormalities, forgetfulness, dry skin and hair, hoarse voice and intolerance to cold.

In addition, both hyperthyroidism and hypothyroidism can be accompanied by an enlargement of the thyroid gland known as goitre.

Who is affected by thyroid disease?

On a worldwide scale, it is estimated that more than 200 million people have some form of thyroid disease. People of all ages and races can get thyroid disease. However, women are 5 to 10 times more likely than men to develop problems with their thyroid function.

What causes thyroid disease?

There are different factors that can cause hyper- and hypothyroidism.

The following conditions cause hypothyroidism:

Thyroiditis is inflammation of the thyroid gland. This can reduce the amount of thyroid hormones produced.

A special form of thyroiditis is Hashimoto’s thyroiditis. This is a genetic disorder that causes the immune system to make the thyroid gland underactive. Hashimoto’s thyroiditis often runs in families. In addition, thyroiditis can occur in women after giving birth, this is called postpartum thyroiditis. Postpartum thyroiditis is usually a temporary condition and occurs only in 5-9% of woman giving birth.

Nutrition also impacts the function of your thyroid gland. 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.

Medications, radioactive iodine treatment and thyroid surgery and conditions affecting the pituitary gland can also result in hypothyroidism.

The following conditions cause hyperthyroidism:

Graves’ disease is a condition where the immune system causes the thyroid gland to become overactive and produce too much hormone. Your thyroid gland might be enlarged and referred to as a diffuse toxic goitre.

Thyroiditis (inflammation) caused by a viral infection can 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, with thyroid function returning to normal in most cases.

Excessive iodine intake may have negative effects on your thyroid gland. High quantities of iodine are found in a number of drugs such as Amiodarone, Lugol’s solution (iodine), some cough syrups and contrast dyes used for some types of scans. This might cause the thyroid to produce either too much or too little thyroid hormones in some individuals.

Swelling and lumps can occur within the thyroid gland, and they are called nodules. Most thyroid nodules are harmless, but some can cause the overproduction of thyroid hormones. Rarely, thyroid nodules can be cancerous. In some cases, such as cancer, some or all of the thyroid gland is removed. You can live without your thyroid, but you need to take medicine daily to replace the hormones produced by your thyroid gland.

How can I promote the health of the thyroid gland?

Iodine is the critical ‘ingredient’ for the production of thyroid hormones. We don’t need a lot of iodine, but a daily and constant supply of this micronutrient is important. Too much iodine can cause problems with your thyroid gland as described above. The best way to get your daily dose of iodine is through eating foods like seafood and dairy products. In addition, iodized salt (salt with iodine added to it) is a good source of iodine and you can use it to season your food.

Last reviewed: Jan 2020


its functions and diseases – FGBU “NMITs TPM” of the Ministry of Health of Russia

The thyroid gland plays an important role in the work of our body, if it does not function properly, metabolic processes are disrupted, and other systems malfunction. It is no coincidence that one day of the year was dedicated to this organ – today, May 25, is World Thyroid Day.

Alla Makarovskaya, a doctor-endocrinologist of the National Medical Research Center for Therapy and Preventive Medicine of the Russian Ministry of Health, told about how the thyroid gland is arranged, what hormones it produces and what function it performs.

“The thyroid gland is one of the largest endocrine glands, located under the larynx, anterior to the trachea, consists of two lobes and an isthmus (has the shape of a butterfly).

The name “thyroid” was given to it by the anatomist Thomas Worth in 1656; iron in its shape reminded him of the shields of the warriors of Ancient Greece. And the first mention of the thyroid gland dates back to the 4th century BC. – they were found in the writings of Hippocrates and Plato, in the writings of physicians in ancient Greece, India and Egypt. According to WHO statistics, among endocrine disorders, thyroid diseases are the second most common after diabetes mellitus.

This “butterfly” gland has its own holiday: May 25 is World Thyroid Day. The date was proposed in 2008 by the European Thyroid Association.

The thyroid gland produces hormones: thyroxine (T4) and triiodothyronine (T3), which, released directly into the blood, affect all cells and tissues of the body, regulate the rate of various metabolic processes, thereby affecting the functions of all organs and systems .

In the blood, most of the thyroid hormones are associated with proteins, they are biologically inactive, and only a small fraction of hormones free from proteins actively performs their functions (free T3 and free T4). The “conductor” of the work of the entire endocrine system is the hypothalamic-pituitary system, which consists of two glands: the pituitary gland, located at the base of the brain, and the hypothalamus, located in the brain a little higher than the pituitary gland.

Thyroid, pituitary and hypothalamus work in concert to control thyroid hormone levels. If, for example, there is not enough thyroid hormone in the blood, the pituitary gland increases the production of its thyroid-stimulating hormone (or TSH), which stimulates an increase in the production of hormones by the gland. Once normal thyroid hormone levels are restored, TSH production slows down and approaches normal.

The state of normal functioning of the thyroid gland is called euthyroidism (“eu-” in Greek means “good”, “normal”). If the thyroid gland does not produce enough hormones, then the metabolic processes in the body slow down. This condition is called hypothyroidism.

If there is more thyroid hormone than necessary, the metabolism increases and the opposite state of hypothyroidism develops – hyperthyroidism.

The symptoms of hypo- and hyperthyroidism are not specific to thyroid disorders, they can be associated with completely different problems. In order to accurately assess the activity of the thyroid gland, it is enough to donate blood, in which the level of TSH, free T4 and free T3 is primarily assessed.

Goiter refers to an enlarged thyroid gland. Currently, an accurate method for determining its size and structure is ultrasound (ultrasound). Autoimmune thyroid diseases are widespread. Diseases of this type are diffuse toxic goiter (DTG) and autoimmune thyroiditis (AIT). Each of these occurs in about one in 100 people.

Other thyroid diseases are nodules, cancer, subacute thyroiditis. For the differential diagnosis of nodular goiter (thyroid nodules larger than 1 cm in diameter), a fine needle aspiration biopsy (FNA) is indicated.

You can make an appointment with an endocrinologist at the Consultative and Diagnostic Center of the National Medical Research Center for Therapy and Preventive Medicine of the Russian Ministry of Health by calling 8 (495) 790-71-72.

Pathology of the thyroid gland

The territory of Moscow and the Moscow Region belongs to areas with a low content of iodine in drinking water, which, along with ecology and carcinogenic food, leads to various diseases of the thyroid gland.

The thyroid gland is one of the most important organs of the human endocrine system. Thyroid hormones regulate such important body functions as metabolism, growth, mental development, the activity of the cardiovascular and digestive systems, participation in the regulation of sexual function. Thyroid dysfunctions include diseases hyperthyroidism and hypothyroidism .

Hypothyroidism syndrome (thyrotoxicosis) is more often diagnosed with diffuse toxic goiter (DTG) and is caused by increased production of thyroxine and triiodothyronine by the thyroid gland. DTG is diagnosed mainly in young and middle-aged women.

The exact cause of the development of the disease cannot be named for certain, however, the factors that provoke it are:

  • autoimmune reaction of the body (production of antibodies that activate the thyroid gland and hormone production)
  • mental trauma

Under the influence of any of these factors, the thyroid gland can increase in volume, increase the secretion of its hormones, which leads to the development of hyperthyroidism.

Hypothyroidism is a syndrome characterized by insufficient production of thyroid hormones (thyroxine and triiodothyronine).

Hypothyroidism is associated with neuropsychiatric disorders, metabolic and energy disorders in the body, swelling of the face, bradycardia (slow pulse). It is more common in women aged 30-50 years.

Symptoms of hyperthyroidism: psychosomatic disorders, the most common of which are excessive irritability, constant feeling of fatigue and weakness, increased sweating, heat intolerance, etc. General examination sometimes reveals a slightly enlarged thyroid gland, tachycardia, low or high blood pressure; weight decreases, diarrhea, lacrimation, “bulging eyes” are possible.

The cause of the disease can be:

  • chronic thyroiditis
  • congenital thyroid disorders
  • environmental iodine deficiency
  • surgery and trauma of the thyroid gland
  • Radiation or thermal treatment of the gland
  • treatment with iodine-containing drugs, antithyroid drugs.