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Hyperthyroidism

What Is Hyperthyroidism?

Last updated on:
21/04/2013

Contributing Author: Guy Slowik FRCS

Hyperthyroidism is a condition in which there is overproduction of thyroid hormone by the thyroid gland, causing the levels of thyroid hormone in the blood to be too high. People who have it are often said to have an "overactive thyroid".

  • The thyroid gland is a small, butterfly-shaped organ located in the neck below and in front of the Adam's apple.
  • Thyroid hormone is a chemical substance produced by the thyroid gland and released into the bloodstream. It interacts with almost all body cells, causing them to increase their metabolic activity.

This abnormally high level of thyroid hormone typically speeds up the body's metabolism. Metabolism is the chemical and physical processes that create the substances and generate the energy needed for cell function, growth, and division.

Symptoms of hyperthyroidism may include a rapid heartbeat, tremor of the fingers and hands, weight loss, and the inability to tolerate heat.

Nice To Know:

About the thyroid gland

The thyroid lies just under the Adam's apple in the neck. There are two lobes to the gland, and they lie just in front and at either side of the windpipe (trachea).

The thyroid is part of the body's endocrine system, which consists of glands that secrete hormones into the bloodstream.

The thyroid gland secretes thyroid hormones, which control the speed at which the body's chemical functions proceed (metabolism). To produce thyroid hormones, the thyroid gland needs iodine, an element contained in food and water.

The thyroid gland also produces a hormone, called calcitonin, which is involved in the metabolism of our bones.

What Is Thyroid Hormone?

Hormones are chemical messengers released into the bloodstream by specialized glands called endocrine glands.

The hormone circulates through the body in the bloodstream delivering a message to other parts of the body. The "message" causes effects far from the gland that produced the hormone.

Thyroid hormone is produced in the thyroid gland, which is located in the front of the neck. It is released by the thyroid gland into the bloodstream and circulates throughout the body. Almost every cell in the body, from those in the brain to those in the feet, responds to the hormone.

There are two different forms of thyroid hormone present in the bloodstream. The two forms of thyroid hormone differ in the number of iodine units or molecules attached to the hormone. Iodine is a very important component of thyroid hormone.

  • Thyroid hormone with four iodine units is abbreviated as T4.
  • Thyroid hormone with three iodine units is abbreviated as T3.
  • Most thyroid hormone in the blood is T4.
  • T3 is the form that is active in the body, not T4.
  • Certain cells in the body convert T4 to T3.

Nice To Know:

Just about all the iodine we consume in food is used for the production of thyroid hormone. Iodine is added to regular table salt to ensure that individuals get enough iodine in their diets. Salt boxes are usually labeled "iodized salt." People with deficiency in iodine will develop hypothyroidism, a condition in which the circulating levels of thyroid hormone are too low.

For more information about hypothyroidism, go to Hypothyroidism.

For further information about hypothyroidism, go to Hypothyroidism.

What Does Thyroid Hormone Do?

Cells respond to thyroid hormone with an increase in metabolic activity. Metabolic activity, or metabolism, is a term used to describe the processes in the body that produce energy and the chemical substances necessary for cells to grow, divide to form new cells, and perform other vital functions.

If you think of each cell in the body as a car, then thyroid hormone acts as if you were tapping on the accelerator pedal. Its message is "go."

Because thyroid hormone stimulates cells, it causes major body functions to "go" a bit faster.

  • Heart rate increases.
  • Breathing rate increases.
  • Use of proteins, fats, and carbohydrates increases.
  • Skeletal muscles work more efficiently.
  • Muscle tone in the digestive system, such as those in the walls of the intestines that help to move food through the digestive system increases.
  • Mental alertness and thinking skills are sharpened.

How Are Blood Levels Of Thyroid Hormone Controlled?

Normally, the body runs like a car on cruise control-functioning at a steady rate. This steady state is known as homeostasis. The body's control system that regulates the cells to function at a steady, appropriate metabolic rate may be explained as follows:

  • Special "detector" cells in the brain monitor the level of thyroid hormone in the blood.
  • When the level of thyroid hormone drops, these cells send signals to a nearby organ in the brain known as the pituitary gland.
  • These signals stimulate the pituitary gland to release a substance called thyroid-stimulating hormone (TSH) into the bloodstream.
  • TSH signals cells in the thyroid gland to release more thyroid hormone into the bloodstream.
  • When the blood level of thyroid hormone has increased enough, the detector cells in the brain detect the increase in thyroid hormone level.
  • These detector cells send signals to the pituitary gland to stop release of TSH.

Nice To Know:

The medical specialty called endocrinology is devoted to the study and treatment of disorders of endocrine glands, including hyperthyroidism. Primary care physicians refer individuals to an endocrinologist for a consultation and ongoing care for hyperthyroidism or other endocrine conditions.

Facts about hyperthyroidism

  • Hyperthyroidism is a medical condition characterized by an abnormally high level of thyroid hormone in the bloodstream.
  • Hyperthyroidism is commonly referred to as "overactive thyroid."
  • Hyperthyroidism is also known as thyrotoxicosis from the prefix "thyro-" meaning thyroid, the term "toxic" meaning poisonous, and the suffix "-osis" meaning condition.
  • Thyroid literally means "shaped like a shield." The thyroid gland lies in front of the voice box. The gland and it associated support tissues are shaped like a shield.
  • Symptoms of hyperthyroidism may include a rapid heartbeat, muscle weakness, tremor, weight loss, and the inability to tolerate heat.
  • About one or two in every 100 Americans develop hyperthyroidism. Most of them are women or girls.
  • Each year, about 500,000 Americans are diagnosed with hyperthyroidism.
  • The most common form of hyperthyroidism is Graves' disease. About 95 percent of affected individuals have this form of the disease.
  • Nodular thyroid disease is much less common than Graves' disease as a cause of hyperthyroidism.
  • The three major treatment options-medication, radioactive iodine, and surgery-work by decreasing the amount of thyroid hormone produced. The goal of treatment is to bring the body into homeostasis or a healthy, balanced condition.
  • About 30 percent of people with Graves' disease have associated eye disease. Hyperthyroid eye disease may cause significant changes in vision along with eyes that bulge or protrude from the face. Other problems with the eyes vary greatly and may include discomfort, pain, or excessive tearing to blurry vision or even double vision.

 

 
 
 

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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.