The thyroid is a small hormone-secreting gland just below the"Adam's apple" on the front side of the neck.  The thyroid gland is responsible for secreting a hormone called thyroid hormone.  This hormone travels to the body tissues through the blood and helps regulate the speed at which cells perform chemical processes (metabolism).  Oxygen consumption, use of nutrients, production of chemicals, cell growth and cell replication are all affected by the amount of thyroid hormone in the blood.  When levels of thyroid hormone are abnormally low, the condition is called hypothyroidism.  Children with hypothyroidism may have slow growth, weight gain, constipation, low energy, cold intolerance, and dry skin.  An overactive thyroid gland causes hyperthyroidism... and symptoms such as weight loss, hyperactivity, jitteriness, and diarrhea.  Thyroid function is measured by simple blood tests and hypothyroidism can be treated with thyroid replacement medications.

What stimulates the production of thyroid hormone?

The body has a complex mechanism for regulating the production of thyroid hormone.  The first signal begins in the brain.  The hypothalamus (a small section of the brain) secretes thyrotropin-releasing hormone.  This hormone causes the pituitary gland at the base of the brain to release a hormone called thyroid stimulating hormone (TSH).  As you may have guessed,TSH stimulates the thyroid to release thyroid hormone.  When blood levels of thyroid hormone rise, the amount of TSH produced decreases and vice versa.  This feedback loop keeps the level of thyroid hormone in the blood at an appropriate level.

How is thyroid hormone made?

Thyroid hormone is produced by the thyroid with the use of iodine ingested in food.  Because iodine is generally found in low levels in the American diet, iodine is now added to salt (iodized salt) to prevent iodine deficiency.  Thyroid hormone is produced by the thyroid in two forms, thyroxine (T4) and triiodothyronine (T3).  T4 has very little hormone activity in the body until it is converted to T3 in the liver and body tissues.  Much of the T4 and T3 is bound to protein in the blood and this is released when it is needed.  

What are T3 and T4? 

Not including the third and fourth movies in the "Terminator" series... Was there a 4th movie?  T3 stands for triiodothyronine. T4 stands for thyroxine. They are two forms of a major hormone secreted by the thyroid gland in response to TSH.  T3 has three iodine atoms and T4 has four iodine atoms.  These amine hormones control multiple body functions including:

• Increase energy production from fats, carbohydrates, and proteins
• Increase protein synthesis

What is TSH?

TSH stands for thyroid stimulating hormone and is sometimes called thyrotropin.  It is a hormone secreted by the pituitary in response to thyrotropin-releasing hormone (TRH) from the hypothalamus.  TSH stimulates the normal growth of the pancreas and also the release of T3 and T4 from the thyroid.  

What is TRH?

TRH stands for  thyrotropin-releasing hormone (TRH) which is secreted from the hypothalamus in response to multiple stimuli.  These stimuli include:

• Stress
• Decreased metabolic rate
• Low body temperature 

What is calcitonin?

Calcitonin is a hormone produced in the pancreas in response to high blood calcium levels.  Calcitonin reduces the release of calcium and phosphorus from the bones to the blood.

Why are there so many thyroid hormones?

There are multiple hormones related to thyroid function.  These hormones stimulate each other in order to create a chain of events, ultimately leading to increased energy production in the body.  There are multiple steps in the process in order to closely regulate this process.  Imagine the worker at a fast food restaurant.  This worker has a boss and the boss has a boss.  The customer can complain to the boss or the boss's boss... which is probably more effective than complaining to the employee directly.

What is hypothyroidism?

Hypothyroidism occurs when the amount of thyroid hormone secreted by the thyroid is too low.  Thyroid hormone is not required to sustain life, however low levels can cause severe medical problems.  Signs of hypothyroidism include: slowing of mental and physical processes, cold sensitivity, poor growth, weight gain, constipation, low energy, dry skin, and thinning hair.

What is hyperthyroidism?

Hyperthyroid occurs when too much thyroid hormone is produced by the thyroid gland.  The symptoms of hyperthyroidism include: weight loss, nervousness, jitteriness, tremor, fast heart rate, and hyperactivity.

Bookmark with: