What does the thyroid do?

Question

I have an underactive thyroid (hypothyroidism), and know the symptoms of it, but was recently asked what the thyroid does. I really didn't know. I thought it was sort of like a helper to all of the different hormones in the body - but I'm not sure.

Answer 1

The Thyroid gland is an endocrine organ which sits about two finger lengths below the cricoid cartlage in the neck. It is under the control of the pituitary gland which is under control of the hypothalamus in the brain.
The hypothalamus secreted TRH (thyroid releasing hormone) which signals to the pituitary to release TSH (thyroid stimulating hormone) from the anterior pituitary or adenohypophysis, which signals to the thyroid to start making thyroid hormones. The thyroid hormones made are T3, T4, calcitonin.
T3 and T4 are made using iodine. Iodine is taken up from the blood stream and is used in a process called iodinization where tyrosine (an amino acid) and iodine combine. Then various forms of pre-thyroid hormones called MIT and DIT use this to combine and form T3 and T4 hormones. T3 and T4 are released into the blood stream where they circulate in both bound and unbound forms. The bound form is when T3 or T4 is attached to a molecule called TBG (thyroid binding globuline), this form is not active in the body. Only the "free" forms have action in the body, and they are in a small concentration. Generally T3 is secreted less than T4 and is much more potent (stronger).
T3 and T4 have many actions in the body which include:
- regulation of cellular metabolism
- regulation of protein metabolism
- Increasing or decreasing the effect epinephrine and norepinephrine have on the body (adrenaline)
- Regulate body temperature
- Regulate heart rate, breathing rate

Calcitonin the other hormone made will counter act PTH (parathyroid hormone) secreted from the parathyroid glands, which sit on the back of the thyroid. PTH will cause cells in the bones called osteoclasts to start to break down bone to release calcium into the blood when calcium is low. Also it will cause the kidneys to take up calcium from the urine. Calcitonin on the other hand causes the inhibition of osteoclasts and the remineralization of bones.

Hypothyroidism is an under secretion of T3, T4, and calcitonin. It may be caused by disruption of the neuro-endocrine pathway with TRH and TSH or one or the other. Or, it may be due to an autoimmune disorder called Hashimotos Thyroiditis where antibodies attach the TSH receptors in the thyroid gland.

Symptoms of hypothyroidism are as follows:
Decreased metabolism: resulting in weight gain
Decreased protein metabolism: resulting in decreased amino acid levels, which can cause problems with skin, hair, nails.
Decreased heart rate and blood pressure from low reaction to adrenaline.
Decreased body temperature

Treatment for this includes: synthetic T4 (Levothyroxine) which will gain maximum action in 4-6 weeks, or T3 (Cytomel) which take 3-6 days for maximum action in the body, but is not as stable as Levothyroxine, so you can get more fluctuations in hormone levels. For Hashimoto's it may be necessary to titrate the dose of medications up and down depending on the function of the thyroid gland at a given period in time.

Answer 2

The hormones secreted by the thyroid gland help regulate the rate at which the body produces energy. They determine how slow or fast your metabolism works. The thyroid is regulated by the pituitary gland.

Answer 3

They thyroid is an endocrine gland in your neck that basically controls energy use by your body. It has effects on most other systems of your body, include heart, brain, gi, and reproductive. It does not create calcium, but, (along with the parathyroid glands), work to maintain calcium levels.

Answer 4

That is a very good basic description. It also creates your calcium and supports pituitary function.

Answer 5

Quite simply-it regulates your metabolism.