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July 03, 2023 9 min read

Have you ever wondered how the body keeps up with the energy it needs to function properly? Imagine your body's metabolism as the engine of an F 150 truck, and thyroid hormones are gasoline, which works as a fuel. You can thank your thyroid gland for producing those hormones to maintain metabolic processes and meet your energy needs.

Without optimal thyroid function, your body will experience slow and sluggishness or other health issues. But what is the thyroid gland? How does it function? Here's everything you need to know.

What is the thyroid gland, and where is it located?

This thyroid gland is a small butterfly-shaped gland, about 2 inches long, located at the front of your neck under the Adam's apple. Although it's small in size, it has a massive function for your body.

During the development of the thyroid gland, the gland is shaped like a tube and is at the back of your tongue. Over time it will move through the underside of your tongue and finally into the front of your neck. As it grows, the gland will form two lobes and small structures called follicles, which store thyroid hormones. All of these developments will be completed before you are born.

The thyroid gland consists of several components, including:

  1. Follicular cells: These cells produce the primary thyroid hormones – thyroxine (T4) and triiodothyronine (T3).

  2. Parafollicular cells (C-cells): These cells produce another important hormone – calcitonin, which is responsible for regulating calcium levels in the blood and promoting bone health.

How does the thyroid gland work?

The thyroid gland works closely with other parts of the endocrine system, particularly the hypothalamus and the pituitary gland, to regulate thyroid hormone production. This process involves a feedback loop known as the hypothalamic-pituitary-thyroid (HPT) axis, which functions as follows:

  1. The hypothalamus, a part of the brain that oversees hormone regulation, detects low thyroid hormone levels in the blood. It responds by releasing thyrotropin-releasing hormone (TRH).

  2. TRH stimulates the pituitary gland, another part of the brain involved in hormone regulation, which then releases thyroid-stimulating hormone (TSH).

  3. TSH signals the thyroid gland to produce and release T4 and T3 hormones into the bloodstream.

  4. As T4 and T3 hormone levels increase, the hypothalamus and pituitary gland receive negative feedback, reducing the production of TRH and TSH, effectively maintaining a balance in thyroid hormone levels.

What are the hormones produced by the thyroid gland?

One of the main functions of the thyroid gland is to produce hormones that regulate the body's metabolic rate, which is your body's process of producing the food you consume into energy. Remember that all the cells in your body need energy to function, just like your vehicle needs gasoline to take you to your destination.

The primary hormones secreted by the thyroid gland are:

Thyroxine (T4)

Thyroxine (T4) is the primary hormone secreted by the thyroid gland. Composed of four iodine atoms attached to a tyrosine-based structure, T4 is a prohormone, meaning it is the precursor to the more biologically active thyroid hormone, triiodothyronine (T3). In fact, T4 accounts for approximately 90% of the total hormone production in the thyroid gland.

Function and importance of T4

Although T4 is considered a prohormone and less active than T3, it plays a significant role in maintaining general health and homeostasis within the body. Its primary functions include:

  1. Metabolism regulation: Thyroxine is responsible for the pace at which the body uses energy, influencing the metabolic rate of various organs and tissues. It helps regulate body temperature, digestion, and heart rate by driving energy production and utilization.

  2. Growth and development: Adequate levels of T4 are crucial for healthy growth and development, particularly during infancy and childhood. T4 is involved in cognitive development, bone growth, and overall physical development.

  3. Conversion to T3: As a prohormone, T4 is converted into the more active thyroid hormone, T3, in peripheral tissues like the liver and kidneys. This conversion ensures the availability of adequate T3, which plays an even more prominent role in metabolism regulation and maintaining overall energy levels.

Triiodothyronine (T3)

Triiodothyronine, or simply T3, is another important hormone made by the thyroid gland. The name T3 comes from the three iodine atoms connected to its main structure. Even though the thyroid gland produces more of the T4 hormone, T3 is known as the active thyroid hormone. This is because it connects better with the body's hormone receptors and has a stronger impact on the tissues it targets.

Function and importance of triiodothyronine (T3)

As the active thyroid hormone, T3 has a significant impact on various aspects of health, including:

  1. Metabolism regulation: The primary function of T3 is its role in regulating the body's metabolism, which refers to the pace at which the body uses energy. T3 acts on almost every cell in the body, affecting the metabolic rate of organs and tissues, and helps maintain body temperature and energy levels.

  2. Cardiovascular health: T3 directly impacts the heart by regulating both the heart rate and the force at which the heart pumps blood. It ensures proper oxygen supply to tissues and the efficient removal of waste products, maintaining overall cardiovascular health.

  3. Growth and development: Adequate levels of T3 are crucial for healthy growth and development, particularly during infancy and childhood. T3 contributes to brain development, bone growth, and overall physical development.

  4. Mood and cognition: T3 is essential for normal brain functioning, maintaining mood stability and cognitive function. Imbalanced T3 levels may lead to mood and memory disturbances.

Production and conversion of T3

T3 is produced in the thyroid gland, although the majority of T3 circulating in the body is derived from the conversion of thyroxine (T4) in peripheral tissues, such as the liver and kidneys. This conversion is facilitated by an enzyme called deiodinase, which removes one iodine atom from T4, creating the active form T3. This process ensures that the body maintains adequate levels of the more potent hormone T3 when necessary.

Other hormones

You may have heard of the thyroid hormones T3 and T4 very often. Apart from these hormones, there are still some of the same hormones produced by the thyroid gland. Here are other hormones that are also included in the thyroid hormone and are no less important for your body's function:


Calcitonin is another hormone produced by the thyroid gland, specifically by the parafollicular cells, also known as "C-cells," within the thyroid tissue. Although not as well-known as T3 and T4, calcitonin plays a vital role in regulating calcium levels in the blood and maintaining bone health. Here's how calcitonin works:

  1. Calcium regulation: Calcitonin aids in maintaining a balance of calcium levels in the bloodstream. When blood calcium levels are high, calcitonin is released to help lower them back to normal.

  2. Bone health: Calcitonin helps to protect bone health by inhibiting bone resorption, which is the process of breaking down bone tissue to release minerals like calcium into the blood. By reducing bone resorption, calcitonin contributes to maintaining bone strength and density.

Diiodothyronine (T2)

T2, or Diiodothyronine, is another thyroid hormone that is lesser known and more challenging to study due to its low concentration in blood circulation. Consisting of two iodine atoms attached to the tyrosine base, the T2 hormone is formed during the T4-to-T3 conversion process. It is considered an inactive metabolite and was initially believed to possess no significant biological activity.

However, recent research indicates that T2 might play a role in metabolic effects on skeletal muscle and adipose (fat) tissue. In certain situations, it has been found to help modulate energy metabolism and the use of lipids as an energy source, indicating a potential role in maintaining body weight and preventing obesity. Nevertheless, more research is required to fully understand the precise actions and relevance of T2 hormones in human physiology.

Monoiodothyronine (T1)

T1, also known as Monoiodothyronine, is the simplest thyroid hormone. It consists of one iodine atom attached to a tyrosine-based structure. Though not well understood, the T1 hormone is found in small amounts in thyroid tissue and blood circulation. Recent studies suggest that T1 hormones might have specific local actions, particularly in the central nervous system, but more research is needed to understand their full biological role.

What are the roles of thyroid hormones in metabolism and body functions?

Thyroid hormones have a profound impact on overall health, affecting a myriad of bodily functions, particularly metabolism. The thyroid gland, which can occasionally become enlarged due to thyroid disorders or thyroid cancer, produces these critical hormones that regulate the body's energy use. Here are some of them:

1. Regulate metabolism

As we've mentioned before, thyroid hormones, T3 and T4, are crucial for maintaining a healthy metabolic rate - the pace at which the body uses energy. An underactive thyroid (hypothyroidism) results in low thyroid hormone levels, leading to a decrease in metabolic rate, weight gain, and fatigue. Conversely, an overactive thyroid (hyperthyroidism) produces more thyroid hormones than required, increasing metabolism, causing weight loss, and increasing heart rate.

2. Regulate body temperature

Thyroid hormones help to maintain a consistent body temperature by modulating basal metabolic rate. They essentially make the cells of the body work more efficiently, generating heat as a byproduct.

3. Help with growth and development

Adequate thyroid hormone levels are essential for proper growth and development, particularly during infancy and childhood. They directly influence bone growth, brain development, and muscular activity.

4. Stabilize brain function and mood

Thyroid hormones have a significant impact on cognitive function, memory, and mood. Imbalanced hormone levels can lead to cognitive difficulties, memory issues, and mood disorders.

5. Ensure cardiovascular health

The thyroid hormones affect heart rate and blood pressure regulation, ensuring adequate oxygen delivery to tissues and efficient waste removal.

What are the main conditions that can affect the thyroid gland?

Thyroid health is crucial for overall wellness, as this small, butterfly-shaped gland in your neck performs a central role in controlling your body's metabolism. However, numerous conditions can impact the proper functioning of your thyroid. Let's delve into the primary conditions that might affect your thyroid function.

1. Hypothyroidism

This condition arises when your thyroid gland becomes underactive and does not produce enough thyroid hormones to meet your body's needs. Symptoms can range from fatigue and weight gain to depression and slowed heart rate. Hypothyroidism can be caused by an autoimmune disease called Hashimoto's thyroiditis, certain medications, or even surgical removal or radiation of your thyroid. Treatment typically involves taking a thyroid hormone replacement medication, like levothyroxine.

Natural Desiccated Thyroid (NDT), another type of thyroid hormone replacement therapy, has proven effective for many people with hypothyroidism. Unlike synthetic options, NDT is derived from the thyroid glands of pigs and provides a balanced dose of T3 and T4 thyroid hormones, similar to that naturally produced by the human thyroid gland. NDT is available in both medication and supplement form. NDT supplement is available to buy online, such as VitaliThy.

2. Hyperthyroidism

The opposite of hypothyroidism, this condition is characterized by an overactive thyroid that produces an excessive amount of thyroid hormones. This can lead to rapid heartbeat, weight loss, nervousness, and irritability. Hyperthyroidism can be caused by conditions like Graves' disease, inflammation of the thyroid, or certain types of nodules. Treatment options for hyperthyroidism vary from medications that slow down the production of thyroid hormones, to surgery, or radioactive iodine therapy.

3. Thyroid nodules

These are lumps or growths in the thyroid gland. While most thyroid nodules are benign, a small percentage can contain thyroid cancer. Symptoms can often be non-specific, but large nodules can cause a visible lump in the neck, difficulty swallowing, or changes in voice.

4. Thyroiditis

This is an inflammation of the thyroid, which can lead to either hyperthyroidism or hypothyroidism. There are several types of thyroiditis, including Hashimoto's thyroiditis, de Quervain's thyroiditis, and postpartum thyroiditis.

5. Thyroid cancer

Although relatively rare, thyroid cancer occurs when cells in your thyroid grow and multiply rapidly. The most common types are papillary and follicular thyroid cancers. Treatment typically involves surgery followed by radioactive iodine.

6. Enlarged thyroid gland (goiter)

This is an enlargement of the thyroid gland, which can happen in both hypothyroidism and hyperthyroidism. A common cause of goiter around the world is iodine deficiency. Though not often harmful, large goiters can cause difficulty swallowing or breathing and can be visually noticeable.


Thyroid hormones have a substantial influence on metabolism, body functions, and overall health. Maintaining a healthy hypothalamic pituitary thyroid axis and proper thyroid function is crucial for the thyroid gland to work effectively, ensuring a balanced metabolism and preventing an underactive or overactive thyroid. As a critical component of human physiology, understanding the roles of thyroid hormones can lead to better management of thyroid disorders, improved treatment strategies, and enhanced quality of life for those affected.

If you feel a change in body weight, hair loss, feel tired quickly, and have several other symptoms related to your thyroid health, immediately contact the nearest health facility to see if you have a thyroid disease or any other health condition.

Wojciech Majda
Wojciech Majda

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