Your Thyroid Gland

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

The thyroid is part of a complex communication system in the body. The exchange of information between two glands associated with the brain (hypothalamus and pituitary) and the thyroid helps control hormones necessary to regulate and maintain the body’s metabolism.2

The functions of the thyroid gland2

The pituitary gland instructs the thyroid to release two hormones, triodothyronine (also known as “T3”) and thyroxine (also known as “T4”).  T3 and T4 are referred to collectively as thyroid hormone.  Increasing or decreasing levels of these thyroid hormones in the blood result in a feedback system to the brain, which in turn directs the thyroid to make more or less thyroid hormone.2 The pituitary gland keeps checking the amount of thyroid hormone in the blood.3 If thyroid hormone is low, the brain releases thyroid stimulating hormone (TSH) to signal the thyroid to make more thyroid hormone. Similarly, if thyroid hormone is high, the brain decreases TSH production.2,4

Thyroid hormones2,4

What Does the Thyroid Do?

The purpose of the thyroid is to produce, store, and release thyroid hormones into the bloodstream.  These hormones, called T3 and T4, affect almost every cell in the body and help control metabolism.  Thyroid cells create T3 and T4, which are then released into the bloodstream and transported throughout the body where they control metabolism5, the process by which cells convert substances to energy.  If there is too little thyroid hormone in the blood, metabolism slows down.  This condition is called hypothyroidism.  If there is too much thyroid hormone in the blood, metabolism speeds up.  This condition is called hyperthyroidism.2,6,7

Thyroid hormones regulate vital body functions8

 

How Does the Thyroid Work?

A gland located at the base of the brain, the pituitary gland or pituitary, controls the amount of thyroid hormone produced by the thyroid.  A 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 TSH, which in turn stimulates the thyroid to release T3 and T4. These glands all work together to control the amount of thyroid hormone in the body.2,4 As shown in the graphic below, the regulation of thyroid hormones is controlled by a feedback loop. The aim is to normalize T3 and T4 concentrations.

The feedback system involving the hypothalamus, pituitary, and thyroid9

These organs work 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 hormone. If the level is low, the pituitary gland releases TSH to signal the thyroid to “turn on the heat” by producing more thyroid hormone. The thyroid hormones are then released directly into the bloodstream where they are used to regulate a number of body functions as outlined above.2,4,6

References

  1. Dorion D. Thyroid anatomy. 2015. http://reference.medscape.com/article/835535-overview. Accessed Dec 7, 2015.
  2. Mariotti S. Physiology of the Hypothalamic-Pituitary Thyroidal System. Thyroid Disease Manager. 2011. http://www.thyroidmanager.org/chapter/physiology-of-the-hypothalmic-pituitary-thyroidal-system/. Accessed Nov 8, 2015.
  3. Hormone Health Network. What does the thyroid gland do? 2016. http://www.hormone.org/hormones-and-health/what-do-hormones-do/what-does-the-thyroid-gland-do. Accessed Jan 4, 2016.
  4. Larsen: Williams Textbook of Endocrinology, 10th edition. Copyright 2003 Elssevier.
  5. Sargis, RM. Endocrineweb. How Your Thyroid Works. 2015. http://www.endocrineweb.com/conditions/thyroid/how-your-thyroid-works. Accessed Jan 8, 2016.
  6. PubMed Health. How does the thyroid work? 2015. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072572/ Accessed Nov 8, 2015.
  7. Leung A, Mestman J. Globl Libr. Women’s med. 2015; DOI 10.3843.
  8. Brady, B. Endocrineweb. Thyroid Gland, How it Functions, Symptoms of Hyperthyroidism and Hypothyroidism. 2015. http://www.endocrineweb.com/conditions/thyroid-nodules/thyroid-gland-controls-bodys-metabolism-how-it-works-symptoms-hyperthyroid). Accessed Nov 8, 2015.
  9. Mescher AL: Junqueira’s Basic Hostology: Text and Atlas, 12th edition.  Copyright The McGraw-Hill Companies, Inc.

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

IMPORTANT SAFETY INFORMATION

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.)

ADVERSE REACTIONS

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

USE IN SPECIFIC PATIENT POPULATIONS

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.

INDICATIONS AND USAGE

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.

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.

See full Prescribing Information for more details.

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