What Is Hyperthyroidism?

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.

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.

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.