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Thyroid Gland: Overview

How this endocrine gland functions, and what symptoms might be a clue for hyperthyroidism and hypothyroidism

The thyroid gland is a butterfly-shaped organ located in the base of your neck. It releases hormones that control metabolism—the way your body uses energy. The thyroid’s hormones regulate vital body functions, including:

  • Breathing
  • Heart rate
  • Central and peripheral nervous systems
  • Body weight
  • Muscle strength
  • Menstrual cycles
  • Body temperature
  • Cholesterol levels
  • Much more!

The thyroid gland is about 2 inches long and lies in front of your throat below the prominence of thyroid cartilage sometimes called the Adam's apple. The thyroid has two sides called lobes that lie on either side of your windpipe, and is usually connected by a strip of thyroid tissue known as an isthmus. Some people do not have an isthmus, and instead have two separate thyroid lobes.

How the Thyroid Gland Works

The thyroid is part of the endocrine system, which is made up of glands that produce, store, and release hormones into the bloodstream so the hormones can reach the body's cells. The thyroid gland uses iodine from the foods you eat to make two main hormones:

  • Triiodothyronine (T3)
  • Thyroxine (T4)

It is important that T3 and T4 levels are neither too high nor too low. Two glands in the brain—the hypothalamus and the pituitary communicate to maintain T3 and T4 balance.

The hypothalamus produces TSH Releasing Hormone (TRH) that signals the pituitary to tell the thyroid gland to produce more or less of T3 and T4 by either increasing or decreasing the release of a hormone called thyroid stimulating hormone (TSH).

  • When T3 and T4 levels are low in the blood, the pituitary gland releases more TSH to tell the thyroid gland to produce more thyroid hormones.
  • If T3 and T4 levels are high, the pituitary gland releases less TSH to the thyroid gland to slow production of these hormones.

Why You Need a Thyroid Gland

T3 and T4 travel in your bloodstream to reach almost every cell in the body. The hormones regulate the speed with which the cells/metabolism work. For example, T3 and T4 regulate your heart rate and how fast your intestines process food. So if T3 and T4 levels are low, your heart rate may be slower than normal, and you may have constipation/weight gain. If T3 and T4 levels are high, you may have a rapid heart rate and diarrhea/weight loss. The effects of too much or too little T3 and T4 in your body are discussed in more detail in the next section.

Diseases and Disorders of the Thyroid

There are many diseases and disorders associated with the thyroid. They can develop at any age and can result from a variety of causes—injury, disease, or dietary deficiency, for instance. But in most cases, they can be traced to the following problems:
  • Too much or too little thyroid hormone (hyperthyroidism and hypothyroidism, respectively).
  • Abnormal thyroid growth
  • Nodules or lumps within the thyroid
  • Thyroid cancer

Some of the Most Common Thyroid Disorders 

To learn more, read our article about common thyroid problems.
  • Goiters: A goiter is a bulge in the neck. A toxic goiter is associated with hyperthyroidism, and a non-toxic goiter, also known as a simple or endemic goiter, is caused by iodine deficiency.
  • Hyperthyroidism: Hyperthyroidism is caused by too much thyroid hormone. Goiter is sometimes a side effect of hyperthyroidism. Symptoms of hyperthyroidism include anxiety, irritability or moodiness, hyperactivity, sweating or sensitivity to high temperatures, hand trembling, hair loss, and missed or light menstrual periods.
  • Hypothyroidism: Hypothyroidism is a common condition characterized by too little thyroid hormone. In infants, the condition is known as cretinism. Cretinism has very serious side effects, including abnormal bone formation and mental retardation. If you have hypothyroidism as an adult, you may experience symptoms including trouble sleeping, tiredness and fatigue, difficulty concentrating, dry skin and hair, depression, sensitivity to cold temperatures, frequent and heavy periods, and joint and muscle pain. Hypothyroidism often goes unnoticed, sometimes for years, before being diagnosed.
  • Solitary thyroid nodules: Solitary nodules, or lumps, in the thyroid are actually quite common—in fact, it’s estimated that more than half the population will have a nodule in their thyroid. The great majority of nodules are benign. Usually, a fine needle aspiration biopsy (FNA) will determine if the nodule is cancerous.
  •  Thyroid cancerThyroid cancer is fairly common, though long-term survival rates are excellent. Occasionally, symptoms such as hoarseness, neck pain, and enlarged lymph nodes occur in people with thyroid cancer. Thyroid cancer can affect anyone at any age, though women and people over thirty are most likely to develop the condition.
  • ThyroiditisThyroiditis is an inflammation of the thyroid that may be associated with abnormal thyroid function (particularly hyperthyroidism). Inflammation can cause the thyroid’s cells to die, making the thyroid unable to produce enough hormones to maintain the body's normal metabolism. There are five types of thyroiditis, and the treatment is specific to each.
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