thyroid, T3, T4, TSH explained

what isThyroid stimulating hormone(TSH)?

how are their production controlled?

triiodothyronine or T3

The production and release of thyroid hormones, thyroxine and triiodothyronine, is controlled by a feedback loop involving the hypothalamus, pituitary gland and thyroid gland. Activation of thyroid hormones is then controlled in body tissues such as the liver, brain and kidneys by enzymes called deiodinases which convert thyroxine into the active form triiodothyronine. Most of the body’s circulating triiodothyronine (about 80%) is produced in this way. 

The thyroid hormone production system is regulated by a feedback loop so that when the levels of the thyroid hormones thyroxine and triiodothyronine increase, they prevent the release of both thyrotropin-releasing hormone from the hypothalamus and thyroid stimulating hormone from the pituitary gland. This system allows the body to maintain a constant level of thyroid hormones in the body. 

thyroxine or T4

hypothalamus secretes thyrotropin-releasing hormone which stimulates the pituitary gland to produce thyroid stimulating hormone. This hormone stimulates the production of the thyroid hormones, thyroxine and triiodothyronine, by the thyroid gland.

This hormone production system is regulated by a feedback loop so that when the levels of the thyroid hormones (thyroxine and triiodothyronine) increase, they prevent the release of both thyrotropin-releasing hormone and thyroid stimulating hormone. This system allows the body to maintain a constant level of thyroid hormones in the body.

thyroid stimulating hormone or TSH

When thyroid stimulating hormone binds to the receptor on the thyroid cells, this causes these cells to produce thyroxine and triiodothyronine and release them into the bloodstream. These hormones have a negative effect on the pituitary gland and stop the production of thyroid stimulating hormone if the levels of thyroxine and triiodothyronine are too high. They also switch off production of a hormone called thyrotropin-releasing hormone. This hormone is produced by the hypothalamus and it also stimulates the pituitary gland to make thyroid stimulating hormone. 

what happens if I produce too much or too little of them?

too much triiodothyronine(T3) or Thyroxine(T4)

Thyrotoxicosis is the name of the condition in which people have too much thyroid hormone in their bloodstreams. It may result from overactivity of the thyroid gland (hyperthyroidism) from conditions such as Graves’ disease, inflammation of the thyroid or a benign tumour. Thyrotoxicosis may be recognised by a goitre, which is a swelling of the neck due to enlargement of the thyroid. Other symptoms of thyrotoxicosis include heat intolerance, weight loss, increased appetite, increased bowel movements, irregular menstrual cycle, rapid or irregular heartbeat, palpitations, tiredness, irritability, tremor, hair thinning or hair loss and retraction of the eyelids, which results in a staring appearance.

too little triiodothyronine(T3) or Thyroxine(T4)

Hypothyroidism is the term for the production of too little thyroid hormone by the thyroid gland. This may be because of autoimmune diseases (such as Hashimoto’s disease), very poor iodine intake or due to some medications. Since thyroid hormones are essential for physical and mental development, untreated hypothyroidism before birth and during childhood can result in learning disability and reduced growth. 

Hypothyroidism in adults results in a slowing of the body’s functions with symptoms such as tiredness, intolerance to cold temperatures, low heart rate, weight gain, reduced appetite, poor memory, depression, stiffness of the muscles and reduced fertility.

too much Thyroid stimulating hormone or TSH

A simple blood test can measure thyroid stimulating hormone in the circulation. If a person has too much, this may indicate that their thyroid gland is not making enough thyroid hormone, that is, they have an underactive thyroid gland or hypothyroidism. People with an underactive thyroid often feel lethargic, experience weight gain and feel the cold. Their thyroid gland may enlarge to produce a goitre. Treatment is medication in the form of tablets to bring the level of thyroid hormones back to normal. This also reduces the amount of thyroid stimulating hormone in circulation. It is particularly important for pregnant women to have the correct amounts of thyroid stimulating hormone and thyroid hormones to ensure the healthy development of their babies. Thyroid stimulating hormone is one of the hormones measured in newborns. Rarely, problems from the pituitary gland or rare genetic conditions can result in inappropriately high thyroid stimulating hormones, and high free thyroid hormone levels.

too little Thyroid stimulating hormone or TSH

If a person has too little thyroid stimulating hormone, it is most likely that their thyroid gland is making too much thyroid hormone, that is, they have an overactive thyroid or hyperthyroidism, which is suppressing the thyroid stimulating hormone. People with an overactive thyroid have the opposite symptoms to those with hypothyroidism, they lose weight, feel too hot and can experience palpitations or anxiety. They may also have a slightly enlarged thyroid gland. Treatment is medication in the form of tablets, which reduce the activity of the thyroid gland and return all thyroid hormone levels to normal. Rarely, problems in the pituitary gland can also result in a low thyroid stimulating hormone, and low free thyroid hormone levels. 

how are they connected(summary)?

as mentioned, The thyroid gland takes its direction from both the hypothalamus (which is in your brain) and the pituitary gland, a pea-sized gland at the base of your skull. In a complex dance, the hypothalamus releases something called thyrotropin-releasing hormone, which then triggers the pituitary gland to produce something called the thyroid stimulating hormone (TSH). The TSH is then what helps your thyroid gland release T4 and T3. Without TSH, the system would fail.

Thyroxine (T4) is responsible for your metabolism, mood, and body temperature, among other things. T3, too, is made in the thyroid gland, and it can also be made in other tissues within the body by converting T4 (deiodination) into T3. This hormone is at the center of your digestive and metabolic function, and it also oversees bone health. 

So, if your T3 and T4 levels are too low, the pituitary gland will release more TSH. If they’re too high, the gland will release less TSH — but this give and take system only works if everything is functioning properly.

As mentioned above, the thyroid stimulating hormone (aka thyrotropin or thyrotrophin) is produced by the pituitary gland. It works sort of like the master of the hormones, and rules the production of T3 and T4 from its control center.

If you have too much TSH, it might mean that your thyroid gland isn’t making enough T3 or T4. Remember, the TSH is supposed to stimulate the thyroid gland — but if the gland isn’t responding, then you’ll have too much TSH in your system.

If your TSH levels are too low, it may mean that your thyroid gland is making too much thyroid hormone. This excessive thyroid production could actually suppress the TSH.

A word of warning for pregnant women: It’s incredibly important that your hormones are balanced in pregnancy, as thyroid stimulating hormone plays a role in the development of a healthy fetus.

T3(Triiodothyronine) VS T4(Thyroxine)

T3 refers to a thyroid hormone that influences pretty much every physiological procedure in the body while T4 refers to the principle hormone created by the thyroid organ.