What Is The Function Of The Thyroid?
The thyroid gland is basically the major endocrine gland that regulates the metabolism in the body. It works in conjunction with the hypothalmus upstream and the mitochondria downstream to make sure the body is staying in homeostasis.
The thyroid gland is approximately 2-inches long and is located in front of your throat below the the Adam’s apple. The thyroid has two lobes that lie on either side of your windpipe, and is usually connected by a strip of thyroid tissue known as an isthmus. Some people lack an isthmus, and have two separate thyroid lobes instead.
It has a function in all the following processes.
- Heart rate
- Central and peripheral nervous systems
- Body weight
- Muscle strength
- Menstrual cycles
- Body temperature
- Cholesterol levels
How The Thyroid Functions
It is that T3 and T4 levels are neither too high nor too low. Two glands in the brain—the hypothalamus and the pituitary communicate to maintain T3 and T4 balance.
The hypothalamus produces TSH Releasing Hormone (TRH) that signals the pituitary to tell the thyroid gland to produce more or less of T3 and T4 by either increasing or decreasing the release of a hormone called thyroid stimulating hormone (TSH). 
- When T3 and T4 levels are low in the blood, the pituitary gland releases more TSH to tell the thyroid gland to produce more thyroid hormones.
- If T3 and T4 levels are high, the pituitary gland releases less TSH to the thyroid gland to slow production of these hormones.
The tissue of the thyroid consists of a lot of small individual lobules connected together by connective tissue. These lobules contain a great number of small vesicles, called follicles, which store thyroid hormone in the form of small drops.
The thyroid produces three hormones:
Triiodothyronine or T3
Thyroxine or Tetraiodothyronine, or T4
T3 and T4 are the only true thyroid hormones. They are produced in what are known as the follicle epithelial cells of the thyroid, and iodine is the main component. This makes iodine massively important to function.
This makes. It is a trace element, which means that the body cannot produce it itself, but needs to take it in with food. In the intestine, iodine is taken from the food and enters the circulation stream. In a few steps it is made into the thyroid hormone in the thyroid.
Since the thyroid is vitally important, there is usually always a sufficient amount of T3 and T4 in the body. Some of the hormones are stored in the thyroid while others are bound to carrier proteins in circulation. When the body needs more hormones, T3 and T4 can be released from the proteins in the blood and take their effect. 
The third hormone produced in the thyroid is calcitonin which is involved in calcium and bone metabolism.
T3 and T4 increase the basal metabolic rate, that makes cells work harder and therefore need more energy. This means:
Body temp raises
The heart beats becomes harder and faster
Food is used up more quickly because glycogen is broken down in muscles and liver
- Promotion of brain maturity
- Promotion of growth
Up-regulation of CNS and PNS leads to enhanced attention and faster reflexes
Hot flashes, sweating
- Hair loss
Emotional instability and irritability
Insomnia and restlessness
- High heart rate
There can be many reasons for thyroid over activity. It is often the result of an autoimmune disease of the thyroid called Graves Disease. The thyroid function is normally regulated by TSH produced by the pituitary which controls whether. Sometimes the thyroid cells do not react to this regulating hormone anymore – this is called autonomy.
Too little thyroid and the body functions slow down. This is called hypothyroid and can be from a genetic or develop over type. There can be many different causes for an sluggish thyroid. It can be caused by low iodine levels, so getting enough dietary iodine is of paramount importance. Hashimoto’s thyroiditis, a chronic inflammation of the thyroid, which can also lead to underactivity. Certain medications can also affect the production of thyroid hormones.
Children and babies need to have enough thyroid hormones at an early stage of development can have profound negative effects on physical and emotional development.
- General loss of energy and power
- Slow Metabolism
- Weight gain
- Trouble concentrating, sluggish mental processing
- Cold Sensitivity
Waxy skin (myxedema)
Deep or hoarse voice
Dry, brittle hair
Low sexual desire and impotence
- Possible depression
The thyroid gland can become enlarged in both hyperthyroidism and hypothyroidism. This is called a goiter. It can make breathing difficult by putting pressure on the trachea. 
Putting It All Together
The thyroid is a very complex gland that has control over many tissues and processes. It pretty much runs a lot of human growth and development and daily metabolic functions. When it is functioning well, the body runs smoothly, but when it is over or under performing, problems can arise. It is truly one of the most crucial glands to human health and development. In the part 2 of this article, we will delve into the actual thyroid hormones themselves and what their exact function is.
- Marieb, Elaine Nicpon. Human Anatomy and Physiology, 5th ed. Boston: Addison-Wesley-Longman, 2001.
2. Saladin, Kenneth S. Anatomy and Physiology: The Unity of Form and Function, 2nd ed. Boston: McGraw-Hill, 2001.