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The Thyroid Gland

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The thyroid gland is a crucial hormone gland that is important for the growth, development, and metabolism of the human body. Read the article to know more.

Medically reviewed by

Dr. Nagaraj

Published At March 27, 2023
Reviewed AtDecember 22, 2023


The thyroid is a butterfly-shaped gland at the base of the neck. It also ranks among the largest endocrine glands, weighing 25 to 30 g on average. Each of the two lobes of this gland, which is located on either side of the trachea, measures 4 to 6 cm in length and 1.3 to 1.8 cm in width.

The thyroid is made up of C-cells, which secrete the hormone calcitonin, and thyroid follicle cells (thyrocytes), which produce and store thyroid hormone (primarily T3 and T4).

The thyroid gland secretes two hormones, Triiodothyronine (T3) and Thyroxine (T4), as its main functions. The T3 and T4 hormones both have a significant impact on almost all body tissues.

The thyroid gland is situated in front of the throat beneath the Adam's apple-shaped prominence of the thyroid cartilage. The thyroid has two sides, or lobes, located on either side of the windpipe and is typically connected by an isthmus, a thin band of thyroid tissue. However, some people have two distinct thyroid lobes rather than an isthmus in their thyroid.

What Are the Functions of the Thyroid Gland?

The thyroid gland generates hormones that control the body's metabolic rate, which affects bone growth and maintenance, heart, muscle, and digestive function. The thyroid produces and secretes hormones because it is an endocrine gland. The following hormones are produced and released by the thyroid:

  • Thyroxine (T4): The main hormone produced and released by the thyroid is thyroxine (T4). The thyroid primarily produces this hormone, but it has little impact on the metabolism. Once the thyroid has released T4 into the bloodstream, it can then undergo a process known as deiodination to change to T3.

  • Triiodothyronine (T3): This hormone is produced by the thyroid in smaller amounts than T4 but has a much greater impact on metabolism.

  • Reverse Triiodothyronine (RT3): It is a hormone that the thyroid produces in minimal quantities and counteracts the effects of T3.

  • Calcitonin: This hormone aids in controlling blood calcium levels.

The thyroid gland requires iodine, an element present in food (most frequently, iodized table salt) and water, to produce thyroid hormones. Iodine is captured by the thyroid gland, which turns it into thyroid hormones. Therefore, the amount of hormones the thyroid produces and releases can change due to an iodine deficiency or excess.

The thyroid's hormones control important bodily processes, such as:

  • Breathing.

  • Heart rate.

  • Digestion.

  • Body temperature.

  • Brain development.

  • Body weight.

  • Muscle strength.

  • Menstrual cycles.

  • Cholesterol levels.

  • Mental activity.

  • Skin and bone maintenance.

What Other Organs and Glands Interact With the Thyroid?

The endocrine system is a complex web of hormones and glands. Many glands and hormones depend on other glands and hormones to signal them to begin producing their own products. Additionally, some hormones have the ability to inhibit others.

A complex system manages the level of thyroid hormones in the body. Thyroid-releasing hormone (TRH) is first released by the hypothalamus, a region of the brain located beneath it, and it prompts the pituitary gland to release thyroid-stimulating hormone (TSH). If the body has enough iodine, TSH prompts the thyroid follicular cells to release thyroxine (T4) and triiodothyronine (T3) when blood levels of T3 and T4 are low. Conversely, high T3 and T4 levels cause the pituitary gland to release less TSH to the thyroid gland, which slows the hormones' production. Almost every organ system in the body is impacted by the thyroid gland and its hormones, including:

  • The Cardiovascular System: The thyroid contributes to the control of the heart rate, cardiac output (the amount of blood the heart pumps through the circulatory system), and the force and vigor of the heart contractions (contractility of the heart).

  • The Nervous System: Thyroid problems can result in symptoms that affect the nervous system, such as tingling, pain, or a burning sensation in the body parts that are affected. In addition, both hypothyroidism and hyperthyroidism can lead to depression and anxiety.

  • The Gastrointestinal System: The thyroid affects the passage of food through the digestive system (gastrointestinal motility).

  • The Reproductive System: Inconsistent thyroid function can lead to irregular menstrual cycles and problems with fertility.

What Are the Signs and Symptoms of Thyroid Problems?

Symptoms of various thyroid conditions vary. There are some symptoms to watch out for that could be a sign of a thyroid condition; however, since the thyroid plays a significant role in some body systems and processes, such as heart rate, metabolism, and temperature control, including:

  • Slow or rapid heart rate.

  • Unexplained weight loss or gain.

  • Heat or cold tolerance difficulty.

  • Depression or anxiety.

  • Irregular menstrual periods.

A doctor must be consulted about getting a blood test to check the thyroid function if any of the symptoms are present.

What Are the Routine Examinations Used to Evaluate Thyroid Health?

  • A blood test that measures the levels of thyroid-stimulating hormone (TSH) is the primary procedure for determining the condition of the thyroid. Both hypothyroidism and hyperthyroidism can be detected by this test.

  • TSH blood test normal range is typically 0.5 to 5.0 mIU/L. (milli-international units per liter). However, this can differ from lab to lab and depending on a few things like age and pregnancy. The thyroid hormones T4 and T3 can also be measured in the blood.

  • If the test results are abnormal, the doctor might advise getting an imaging test like a thyroid scan or thyroid ultrasound, which produces images of the thyroid by using very small amounts of a safe, radioactive substance.

What Causes a Thyroid Disorder?

The thyroid gland typically produces precisely the right amount of hormones to maintain a healthy and balanced metabolism in the body. TSH, a hormone secreted by the pituitary gland, circulates in the blood continuously, but its levels can change depending on the amount of T4 present in the blood. The levels of T4 in the blood are kept constant by this hypothalamic-pituitary-thyroid feedback loop, which also responds quickly to small changes.

However, there are several thyroid disorders, most of which have to do with thyroid hormone production. The body uses energy more quickly or more slowly than it should if the thyroid gland either produces too much hormone (hyperthyroidism) or not enough hormone (hypothyroidism).

The various thyroid disorders have a wide range of causes. The autoimmune thyroid disease, a self-destructive process in which the body's immune system attacks the thyroid cells as though they were foreign cells, is the most frequent cause of the condition. In response, the thyroid gland either becomes overactive (hyperthyroidism) or underactive (hypothyroidism). Hashimoto's thyroiditis is the medical term for the autoimmune form of hypothyroidism. Graves' disease is an autoimmune form of hyperthyroidism.

How Can Thyroid Disorders Be Treated?

  • There are treatments for thyroid disorders and to manage many of the symptoms as well. Daily medication is used to treat the majority of thyroid disorders. If medication is unable to control the thyroid disorder, there are other options available.

  • Levothyroxine is a synthetic man-made hormone that can be used to treat thyroid issues like hyperthyroidism in place of thyroxine ( or L-thyroxine). It is an oral and injectable medication that can restore the thyroid glands' normal balance. Patients will notice a decrease in their hyperthyroidism symptoms a few weeks after starting their medication.

  • Radiation therapy could be used to treat thyroid cancer successfully. Sometimes it would be challenging to diagnose thyroid cancer because it has no visible symptoms. A regular checkup is necessary to stop these diseases.

  • Iodine is crucial for keeping the thyroid healthy. The essential "ingredient" needed to produce thyroid hormones is iodine. One teaspoon of iodine is said to be sufficient for a lifetime, so we do not require much of it. However, it is crucial to have a consistent daily supply of this micronutrient. Consuming too much iodine at once can cause the thyroid to produce fewer hormones, which is counterproductive. Eating wholesome foods like seafood and dairy products is the best way to obtain the recommended daily intake of iodine. Iodized salt is also a good source and can be used to season food. To prevent goiters, iodine is added to salt (caused by hypothyroidism).


The thyroid is a significant gland in the endocrine system that has a wide range of physiological effects. The disease of thyroid is very common and curable. A healthcare provider must be consulted if one has any symptoms of thyroid disease. Further, a regular checkup is recommended for healthy living.

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Dr. Nagaraj
Dr. Nagaraj



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