What is the Thyroid?

The thyroid gland, or thyroid, is located at the base of the neck just below the Adam’s apple. It is the shape of a butterfly. One wing, or “lobe,” of the thyroid is located on each side of the trachea (often referred to as the “windpipe”).1

The thyroid gland

Thyroid gland diagram

What Does the Thyroid Do?

The purpose of the thyroid is to:

  • produce thyroid hormones
  • store thyroid hormones 
  • release them into the bloodstream.

Thyroid hormones regulate vital body functions3

thyroid hormones triiodothyronine & thyroxine regulate body functions

There are two types of thyroid hormones, triiodothyronine (also known as “T3”) and thyroxine (also known as “T4”). These hormones affect almost every cell in the body and help control metabolism4 the process by which cells convert substances to energy.

If thyroid hormone levels in the blood are too low, metabolism slows down. This condition is called hypothyroidism.

How is thryoid hormone production regulated2

Thyroid system and hormones

How Does the Thyroid Work?

The pituitary gland or pituitary controls the amount of thyroid hormones produced by the thyroid. The pituitary is located at the base of the brain. Another part of the brain, the hypothalamus, helps the pituitary do its job.

The hypothalamus produces thyroid releasing hormone (TRH), which stimulates the pituitary to release thyroid stimulating hormone (TSH). TSH stimulates the thyroid to release thyroid hormones.

The feedback system involving the hypothalamus, pituitary, and thyroid7

feedback system involving the hypothalamus, pituitary & thyroid

The pituitary, hypothalamus and thyroid all work together in a feedback loop to control the amount of thyroid hormones in the body.2,8

The system works similarly to the way a thermostat controls the temperature in a room. Just as the thermometer in a thermostat senses the temperature of a room, the hypothalamus and pituitary gland sense the amount of thyroid hormones in the bloodstream.

  • If the level is low, the pituitary releases TSH to signal the thyroid to “turn on the heat” by producing more thyroid hormones.
  • If the level is high, the pituitary decreases TSH production to “turn down the heat”

Regulation of thyroid hormone reduction2,5

Thyroid hormones released from pituitary & thyroid gland


Thyroid Cancer Glossary

Low-Iodine Diet

My Doctor Discussion Guide

My Doctor Discussion Guide

More Resources

Thyrogen® (thyrotropin alfa for injection) 0.9 mg/mL after reconstitution


Diagnostic: Thyrogen is used to help identify thyroid disease by testing the blood for a hormone called thyroglobulin in the follow up of patients with a certain type of thyroid cancer known as well differentiated thyroid cancer. It is used with or without a radiology test using a form of iodine.

Limitations of Use:

The effect of Thyrogen on long term thyroid cancer outcomes has not been determined.

When Thyrogen is used to help detect thyroid cancer, there is still a chance all or parts of the cancer could be missed.

Ablation: Thyrogen is also used to help patients prepare for treatment with a form of iodine to remove leftover thyroid tissue in patients who have had surgery to take out the entire thyroid gland for patients with well differentiated thyroid cancer who do not have signs of thyroid cancer which has spread to other parts of the body.

Limitations of Use:

In a study of people being prepared for treatment with a form of iodine after thyroid surgery, results were similar between those who received Thyrogen and those who stopped taking their thyroid hormone. Researchers do not know if results would be similar over a longer period of time.


There have been reports of events that led to death in patients who not had surgery to have their thyroid gland removed, and in patients with thyroid cancer cells that have spread to other parts of the body.

Patients over 65 years old with large amounts of leftover thyroid tissue after surgery, or with a history of heart disease, should discuss with their physicians the risks and benefits of Thyrogen.

Thyrogen can be administered in the hospital for patients at risk for complications from Thyrogen administration.

Since Thyrogen was first approved for use, there have been reports of central nervous system problems such as stroke in young women who have a higher chance of having a stroke, and weakness on one side of the body.

Patients should remain hydrated prior to treatment with Thyrogen.

Leftover thyroid tissue after surgery and cancer cells that have spread to other parts of the body can quickly grow and become painful after Thyrogen administration.

Patients with cancer cells near their windpipe, in their central nervous system, or in their lungs may need treatment with a glucocorticoid (a medication to help prevent an increase in the size of the cancer cells before using Thyrogen.)


In clinical studies, the most common side effects reported were nausea and headache.


Pregnant patients: Thyrogen should be given to a pregnant woman only if the doctor thinks there is a clear need for it.

Breastfeeding patients: It is not known whether Thyrogen can appear in human milk. Breastfeeding women should discuss the benefits and risks of Thyrogen with their physician.

Children: Safety and effectiveness in young patients (under the age of 18) have not been established.

Elderly: Studies do not show a difference in the safety and effectiveness of Thyrogen between adult patients less than 65 years and those over 65 years of age.

Patients with kidney disease: Thyrogen exits the body much slower in dialysis patients and can lead to longer high TSH levels.

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit, or call 1-800-FDA-1088.


  1. Dorion D. Thyroid anatomy. 2015. Accessed January 2019.
  2. Mariotti S. Physiology of the Hypothalamic-Pituitary Thyroidal Axis. Thyroid Disease Manager. 2016. Accessed January 2019.
  3. Brady, B. Endocrineweb. Thyroid Gland, How it Functions, Symptoms of Hyperthyroidism and Hypothyroidism. 2015. Accessed January 2019.
  4. Sargis, RM. Endocrineweb. How Your Thyroid Works. 2015. Accessed January 2019.
  5. PubMed Health. How does the thyroid work? 2015. Accessed January 2019.
  6. Leung A, Mestman J. Globl Libr. Women’s med. 2015; DOI 10.3843.
  7. Mescher AL: Junqueira’s Basic Histology: Text and Atlas, 12th edition. Copyright The McGraw-Hill Companies, Inc.
  8. Larsen: Williams Textbook of Endocrinology, 10th edition. Copyright 2003 Elsevier.