Hibernian Health Check

Thyroid Functions, Facts & Figures

Thyroid Functions, Facts & Figures

Share This Post

Your Thyroid: An Accurate Guide to help you understand your thyroid health

A thorough dive into what your thyroid does and why

Let’s speak about thyroid function. The thyroid gland is one of the major hormone-secreting (endocrine) glands in the body. It is a small butterfly-shaped gland located in front of the windpipe at the base of the throat.

It is composed of two conical right and left lobes that are joined at the front by a central bridge called the isthmus. The thyroid gland is the largest gland of the endocrine system weighting between 15–25g.

The thyroid gland produces two hormones, thyroxine (T4) and triiodothyronine (T3), which are secreted into the blood. These hormones have a vital role in growth and metabolism by regulating the functions of the cardiac, digestive and muscular systems, as well as maintaining healthy bones and normal brain development.

Iodine is needed for the production of thyroid hormones. As iodine is not produced by the body, it needs to come from dietary sources — predominantly seafood and iodized salt. It is thought that up to 30% of people worldwide are iodine deficient. Iodine is particularly important during early pregnancy to help prevent adverse neurodevelopmental outcomes in offspring, as well as in young children.

How are thyroid hormones secreted from the thyroid gland?

The stimulation of the thyroid gland occurs as a part of the hypothalamic–pituitary–thyroid axis.

The hypothalamus, located in the brain, secretes a hormone called thyroid-releasing hormone. This hormone then stimulates the pituitary gland, which is located below the hypothalamus, to release a hormone called thyroid-stimulating hormone (TSH) and it is TSH that triggers the thyroid gland to secrete thyroid hormones.

The production of thyroid hormones is tightly controlled by a feedback loop: if the pituitary gland senses an excess of T3 and T4 in the system, TSH production is reduced, which in turn results in reduced T3 and T4 production by the thyroid gland.

By contrast, if there are low levels of thyroid hormones in the bloodstream, the pituitary gland produces more TSH that stimulates the thyroid gland to secrete more hormones to keep up with the body’s demand.

The majority of T3 and T4 circulating in the body are bound to transport proteins and only very small amounts of T3 and T4 are available as free hormones (unbound) and can directly enter the body’s cells. The thyroid produces more T4 than T3, and much of T3 found in the body has been converted from T4 in a process called deiodination.

 

Testing for thyroid hormones

The primary test (thyroid function test) to check whether the thyroid gland is functioning properly measures TSH and free (unbound) T4 levels. High TSH and low T4 levels can indicate an underactive thyroid gland, whereas an overactive thyroid gland can present as low TSH and high T4 levels.

If you are interested in getting your Thyroid levels checked, you can order one of our kits here.

What is the main function of the thyroid?

Thyroid hormones affect all organs and systems in the body, including the heart, gastrointestinal system, nervous system, bone and metabolism.

Thyroid Hormones undertake the following functions in your body:

  1. Regulate the metabolic rate (the rate at which the body uses calories, which affects weight loss and gain)
  2. Regulate body temperature
  3. Increase heart rate, cardiac output and the contraction of heart muscles
  4. Have a role in respiration and cellular oxygen consumption
  5. Stimulate gut motility
  6. Induce lipid synthesis or lipolysis (breakdown of lipids)
  7. Collaborate with growth hormones in children to stimulate bone growth
  8. Affect fertility, ovulation and menstruation
  9. Help neural cells in the brain to maturate and function properly

Overactive thyroid

An overactive thyroid gland, also known as hyperthyroidism, results in an excess of T3 and T4 and, consequently, decreased levels of TSH. This condition is characterised by increased metabolism and symptoms include:

  1. Weight loss
  2. Palpitations or increased heart rate, which might be associated with abnormal heart rhythms
  3. Fatigue and weakness
  4. Increased appetite
  5. Diarrhoea
  6. Increased sweating
  7. Fine tremors of the hands
  8. Anxiety and restlessness
  9. Heat intolerance (you could struggle in the heat)

Causes of hyperthyroidism

Graves’ disease: an autoimmune disease where the thyroid becoming overactive and produces excessive amounts of thyroid hormones. It is the most common cause of hyperthyroidism.

Thyroid nodules: usually benign (non-cancerous) nodules or lumps that may contain thyroid tissue, which can result in the production of excess thyroid hormones.

Medicines: medications with high iodine content, such as some antiarrhythmic medicines that are used to control irregular heartbeats, can cause hyperthyroidism.

Thyroiditis: inflammation of the thyroid gland can cause excessive production of thyroid hormones.

Underactive thyroid

Underactive thyroid is also known as hypothyroidism. It is a condition in which the thyroid gland does not produce enough thyroid hormones to meet the body’s demand and coincides with increased TSH levels. Thyroid-hormone deficiency results in slower metabolism and this may cause the following symptoms:

  1. Fatigue
  2. High sensitivity to cold weather
  3. Constipation
  4. Weight gain
  5. Muscle weakness, aches and stiffness
  6. Menstrual irregularities
  7. Slower heart rate
  8. Puffy face
  9. Dry skin
  10. Depression and poor memory
    1.  

Causes of hypothyroidism

Hashimoto’s disease: an autoimmune disease in which the thyroid gland becomes inflamed and stops making enough thyroid hormones. It is the most common cause of hypothyroidism.

Thyroiditis: inflammation of the thyroid gland initially causes hyperthyroidism but over time the thyroid gland becomes damaged causing thyroid hormone deficiency.

Surgical removal of part of the thyroid: sometimes after removing part of the thyroid, the remaining tissue stops making thyroid hormones resulting in hypothyroidism.

Radiation therapy: used to treat hyperthyroidism by destroying thyroid cells but can eventually result in hypothyroidism.

Medications: some medicines such as cancer, heart and psychotic medications can interfere with the production of thyroid hormones.

If you would like to get find out more about your Thyroid levels, check out our Home Testing kit here

References

  1. Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. 2021 May 12. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK500006/
  2. Welsh KJ, Soldin SJ. DIAGNOSIS OF ENDOCRINE DISEASE: How reliable are free thyroid and total T3 hormone assays? European journal of endocrinology. 2016. 175, R255–R263. https://doi.org/10.1530/EJE-16-0193
  3. Patil N, Rehman A, Jialal I. Hypothyroidism. 2022 Feb 6. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK519536/

Dr. Olive Leavy, PhD

More To Explore

Health Check

Folate: Folic Acid for Pregnancy & Overall Health

Folate and folic acid are terms that are often used interchangeably to describe the essential water-soluble vitamin, vitamin B9. Folate is the natural form of this vitamin found in food, whereas folic acid is the synthetic form that is added to fortified foods or is found in supplements.

Vitamins

Vitamin B12 – An Every-Day essential

Vitamin B12, also known as cobalamin, is an essential water-soluble vitamin. We cannot make vitamin B12 ourselves and are completely dependent on dietary sources of the vitamin.

It is primarily derived from food of animal origin, such as meat, dairy, poultry, eggs and fish. It is also found in fortified cereals, some fermented foods and fortified nutritional yeast. Vitamin B12 is stored in the liver and this stockpile can last for up to 4 years without replenishment.

Share This Post

Your Thyroid: An Accurate Guide to help you understand your thyroid health

A thorough dive into what your thyroid does and why

Dr. Olive Leavy, PhD

Let’s speak about thyroid function. The thyroid gland is one of the major hormone-secreting (endocrine) glands in the body. It is a small butterfly-shaped gland located in front of the windpipe at the base of the throat.

It is composed of two conical right and left lobes that are joined at the front by a central bridge called the isthmus. The thyroid gland is the largest gland of the endocrine system weighting between 15–25g.

The thyroid gland produces two hormones, thyroxine (T4) and triiodothyronine (T3), which are secreted into the blood. These hormones have a vital role in growth and metabolism by regulating the functions of the cardiac, digestive and muscular systems, as well as maintaining healthy bones and normal brain development.

Iodine is needed for the production of thyroid hormones. As iodine is not produced by the body, it needs to come from dietary sources — predominantly seafood and iodized salt. It is thought that up to 30% of people worldwide are iodine deficient. Iodine is particularly important during early pregnancy to help prevent adverse neurodevelopmental outcomes in offspring, as well as in young children.

How are thyroid hormones secreted from the thyroid gland?

The stimulation of the thyroid gland occurs as a part of the hypothalamic–pituitary–thyroid axis.

The hypothalamus, located in the brain, secretes a hormone called thyroid-releasing hormone. This hormone then stimulates the pituitary gland, which is located below the hypothalamus, to release a hormone called thyroid-stimulating hormone (TSH) and it is TSH that triggers the thyroid gland to secrete thyroid hormones.

The production of thyroid hormones is tightly controlled by a feedback loop: if the pituitary gland senses an excess of T3 and T4 in the system, TSH production is reduced, which in turn results in reduced T3 and T4 production by the thyroid gland.

By contrast, if there are low levels of thyroid hormones in the bloodstream, the pituitary gland produces more TSH that stimulates the thyroid gland to secrete more hormones to keep up with the body’s demand.

The majority of T3 and T4 circulating in the body are bound to transport proteins and only very small amounts of T3 and T4 are available as free hormones (unbound) and can directly enter the body’s cells. The thyroid produces more T4 than T3, and much of T3 found in the body has been converted from T4 in a process called deiodination.

 

Testing for thyroid hormones

The primary test (thyroid function test) to check whether the thyroid gland is functioning properly measures TSH and free (unbound) T4 levels. High TSH and low T4 levels can indicate an underactive thyroid gland, whereas an overactive thyroid gland can present as low TSH and high T4 levels.

If you are interested in getting your Thyroid levels checked, you can order one of our kits here.

What is the main function of the thyroid?

Thyroid hormones affect all organs and systems in the body, including the heart, gastrointestinal system, nervous system, bone and metabolism.

Thyroid Hormones undertake the following functions in your body:

  1. Regulate the metabolic rate (the rate at which the body uses calories, which affects weight loss and gain)
  2. Regulate body temperature
  3. Increase heart rate, cardiac output and the contraction of heart muscles
  4. Have a role in respiration and cellular oxygen consumption
  5. Stimulate gut motility
  6. Induce lipid synthesis or lipolysis (breakdown of lipids)
  7. Collaborate with growth hormones in children to stimulate bone growth
  8. Affect fertility, ovulation and menstruation
  9. Help neural cells in the brain to maturate and function properly

Overactive thyroid

An overactive thyroid gland, also known as hyperthyroidism, results in an excess of T3 and T4 and, consequently, decreased levels of TSH. This condition is characterised by increased metabolism and symptoms include:

  1. Weight loss
  2. Palpitations or increased heart rate, which might be associated with abnormal heart rhythms
  3. Fatigue and weakness
  4. Increased appetite
  5. Diarrhoea
  6. Increased sweating
  7. Fine tremors of the hands
  8. Anxiety and restlessness
  9. Heat intolerance (you could struggle in the heat)

Causes of hyperthyroidism

Graves’ disease: an autoimmune disease where the thyroid becoming overactive and produces excessive amounts of thyroid hormones. It is the most common cause of hyperthyroidism.

Thyroid nodules: usually benign (non-cancerous) nodules or lumps that may contain thyroid tissue, which can result in the production of excess thyroid hormones.

Medicines: medications with high iodine content, such as some antiarrhythmic medicines that are used to control irregular heartbeats, can cause hyperthyroidism.

Thyroiditis: inflammation of the thyroid gland can cause excessive production of thyroid hormones.

Underactive thyroid

Underactive thyroid is also known as hypothyroidism. It is a condition in which the thyroid gland does not produce enough thyroid hormones to meet the body’s demand and coincides with increased TSH levels. Thyroid-hormone deficiency results in slower metabolism and this may cause the following symptoms:

  1. Fatigue
  2. High sensitivity to cold weather
  3. Constipation
  4. Weight gain
  5. Muscle weakness, aches and stiffness
  6. Menstrual irregularities
  7. Slower heart rate
  8. Puffy face
  9. Dry skin
  10. Depression and poor memory
    1.  

Causes of hypothyroidism

Hashimoto’s disease: an autoimmune disease in which the thyroid gland becomes inflamed and stops making enough thyroid hormones. It is the most common cause of hypothyroidism.

Thyroiditis: inflammation of the thyroid gland initially causes hyperthyroidism but over time the thyroid gland becomes damaged causing thyroid hormone deficiency.

Surgical removal of part of the thyroid: sometimes after removing part of the thyroid, the remaining tissue stops making thyroid hormones resulting in hypothyroidism.

Radiation therapy: used to treat hyperthyroidism by destroying thyroid cells but can eventually result in hypothyroidism.

Medications: some medicines such as cancer, heart and psychotic medications can interfere with the production of thyroid hormones.

If you would like to get find out more about your Thyroid levels, check out our Home Testing kit here

References

  1. Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. 2021 May 12. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK500006/
  2. Welsh KJ, Soldin SJ. DIAGNOSIS OF ENDOCRINE DISEASE: How reliable are free thyroid and total T3 hormone assays? European journal of endocrinology. 2016. 175, R255–R263. https://doi.org/10.1530/EJE-16-0193
  3. Patil N, Rehman A, Jialal I. Hypothyroidism. 2022 Feb 6. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK519536/

Dr. Olive Leavy, PhD

Olive gained her PhD in Trinity College Dublin in Immunology. She has enjoyed a varied career including working as an immunologist, researcher, science communicator and Chief Editor for leading scientific journal, Nature Reviews Immunology. Olive has now set up her own business in sustainable forestry management but still maintains her passion for science and education through her articles with Hibernian Health Check.

More To Explore

Health Check

Folate: Folic Acid for Pregnancy & Overall Health

Folate and folic acid are terms that are often used interchangeably to describe the essential water-soluble vitamin, vitamin B9. Folate is the natural form of this vitamin found in food, whereas folic acid is the synthetic form that is added to fortified foods or is found in supplements.

Vitamins

Vitamin B12 – An Every-Day essential

Vitamin B12, also known as cobalamin, is an essential water-soluble vitamin. We cannot make vitamin B12 ourselves and are completely dependent on dietary sources of the vitamin.

It is primarily derived from food of animal origin, such as meat, dairy, poultry, eggs and fish. It is also found in fortified cereals, some fermented foods and fortified nutritional yeast. Vitamin B12 is stored in the liver and this stockpile can last for up to 4 years without replenishment.