Everything you need to know about the Thyroid Stimulating Hormone (TSH). All about the butterfly-shaped gland in our body.
What is Thyroid Stimulating Hormone (TSH)?
TSH stands for Thyroid Stimulating Hormone secreted by the thyroid gland. A H-butterfly shaped gland located in the neck below the Adam’s apple. Hypothalamus releases a substance called as Thyrotropin-releasing Hormone (TRH). The work of the TRH is to give signal to the pituitary gland. Pituitary gland aslo known as master gland. This master gland of the body release Thyroid Stimulating Hormone which makes hormones namely,
- Triiodothyronine (T3)
- Tetraiodothyronine (T4) and is commonly known as thyroxine
Pituitary gland has two parts mainly:
- Anterior lobe
- Posterior lobe
Anterior lobe: This lobe of the pituitary gland produces or releases six main Hormones.
ACTH: ACTH stands for Adrenocorticotropic Hormone. It stimulates the adrenal gland which produces cortisol and other corticotropin related hormones.
- Growth Hormone: The Human Growth Hormone (HGH) helps in the growth, fat metabolism and physical development of the body.
- TSH: Thyroid Stimulating Hormone stimulates the thyroid gland to produce thyroid hormones which regulates the growth and metabolism of the body.
- LH and FSH (the gonadotropins): LH stands for Luteinizing Hormone and FSH stands for Follicle Stimulating Hormone. In men it stimulates the production of the sex hormones which is testosterone. In women it stimulates women sex hormone which is estrogen. It also regulates the menstrual cycle in women.
FSH in women, stimulates the ovaries to produce eggs. In men, it stimulates the testes to produce sperms.
- Prolactin: This hormone is responsible to produce milk at the time of pregnancy by mammary glands.
Posterior lobe: This lobe of the pituitary gland produces or releases two hormones.
- Vasopressin: Also known as Anti-diuretic Hormone (ADH). ADH is responsible for maintaining the amount of water in the blood.
- Oxytocin: Oxytocin in women, stimulates the uterine contraction at the time of childbirth and lactation.
Synthesis of Thyroid Stimulating Hormone
The Hypothalamus releases thyrotropin-releasing hormone (TRH). TRH stimulates and gives signal to the pituitary gland to produce Thyroid Stimulating Hormone. Thyroid Stimulating Hormone produces hormones T3 and T4. This process of synthesis of T3 and T4 occurs in the thyroid interfollicular cells.
The formation of T3 and T4 completes into five steps:
- Iodine uptake
- Oxidation and iodination
- Storage and release
- Peripheral conversion from T4 to T3
Iodine uptake is occurred by the symport named as sodium iodide symport with the help of Thyroid Stimulating Hormone. Here sodium ions transports across the membrane of the follicular cells with the iodide ions.
Tyrosine and Thyroglobulin (TG) are the long chain of amino acids (proteins). These proteins are used in the synthesis of the thyroid hormone.
Oxidation and iodination:
Iodide (I– ) is oxidized by the enzyme thyroperoxidase to iodidium ion (I+ ) or Hypoiodus acid (HOI– ) and Enzyme-linked Hypoiodus (EOI– ). They react with thyroglobulin molecule to form Monoiodothyronine (MIT) and Diiodothyronine (DIT).
In this step, the pairs of iodinated tyrosine residue coupled together to form T3 and T4.
Storage and release:
Thyroglobulin(TG) with MIT and DIT forms T3 and T4. When T3 is require by the body it is utilized after the conversion of T4 to T3.
MIT and DIT are stored outside the cell in the form of colloidal solution. It is taken back into the cells by the process of endocytosis and broken down by the enzyme lysosomal protease whn it is required.
T4 and T3 is release into the circulation while MIT and DIT are deiodonated and recycled and reutilized.
This conversion occurs in the liver and kidney. T4 is converted into T3 which is taken up by targeted cells except brain and pituitary gland. T4 and T3 penetrate cells and combine with nuclear receptors.
Function of Thyroid Stimulating Hormone
The TRH is released by hypothalamus. It stimulates pituitary gland to release Thyroid Stimulating Hormone. Thyroid Stimulating Hormone then releases T4 and T3.
T3 chemically known as 3,5,3’,5’-tetraiodothyronine. T4 known as thyroxine and chemically as 3,5,3’-triiodothyronine. Main function of the T4 and T3 is metabolism and growth of the body.
As T4 and T3 are made up of iodine, if the production of T4 and T3 decreases then there may be iodine deficiency. This causes enlargement of the thyroid gland and causes the disease called simple goiter.
Thyroid Stimulating Hormone Levels
High TSH levels: When a value comes more than the normal tsh levels that is more than 4.0 mIU/L, it indicates that thyroid gland produces less amount of thyroid hormone. That is underactive thyroid gland and is known as Hypothyroidism.
Low TSH levels: When a value comes less than the normal tsh levels that is less than 0.4 mIU/L, it indicates that thyroid gland produces more amount of thyroid hormone. That is overactive thyroid gland and is known as Hyperthyroidism.
Thyroid Stimulating Hormone Range
The normal level of Thyroid Stimulating Hormone is 0.4 to 4.0 milli- International unit per litre.
|S.No.||Category||Time duration||Range (mIU/L)|
|1.||Premature birth||28-36 weeks||0.7-27|
|2.||For children||Birth to 4 days||1-39|
|21 weeks to 20 years||0.7-34|
|3.||For adults||21-54 years||0.4-4.2|
|4.||During pregnancy||First trimester||0.3-4.5|
Thyroid Stimulating Hormone Effects
There may be two types of effects on Thyroid Stimulating Hormone: Positive feedback effect and negavtive feedback effect.
If the level of T3 and T4 is low then thyroid gland will give positive feedback to the pituitary gland to release and stimulate Thyroid Stimulating Hormone.
Also, If the level of T3 and T4 is high then the thyroid gland will give negative feedback to the pituitary gland thus stopping the production of Thyroid Stimulating Hormone.
Side effects of Thyroid Stimulating Hormone includes the symptoms of the thyroid problems- Hypothyroidism and Hyperthyroidism.
Effect of Thyroid Hormones
Somatostatin is the antagonist that means it has an opposite action on the pituitary. Somatostatin reduces the production of Thyroid Stimulating Hormone and inhibits its release. Hence, inhibiting the growth and metabolism of the body.
Effect of Thyroid Stimulating Hormone on pregnancy
The Human Chorionic Gonadotropin (hCG) is a hormone produce by the placenta after implantation.
TSH and hCG has similar properties so there is moderate enlargement of thyroid. There is increase in total serum thyroxine and triiodothyronine. Increase in the Radioactive iodine is done by maternal thyroid.
Thyroid Stimulating Hormone Disorders
Underactive thyroid gland causes Thyroiditis Hypothyroidism causes an autoimmune disease known as Hashimoto thyroiditis. Thyroidits is an inflammation of the thyroid gland. Suffix “Itis” refers to the inflammation. As the name suggest, “Hypo” means low that here refers to low level of thyroid hormones.
Hashimoto disease attacks the thyroid gland which causes fatique, weight gain, painless goiter, constipation, menstrual pain, slower heart rate.
Overactive thyroid gland causes Hyperthyroidism causes an autoimmune disease known as Graves’ disease. As Hypo means low vice versa “Hyper” means High that here refers to high level of thyroid hormones.
In this condition, thyroid gland produces excessive thyroid hormones which causes anxiety, irritability, sweating and weight loss.
TSH levels T3 and T4 levels Disease Condition
High High Tumor of pituitary gland
Low Low Secondary hypothyroidism
Low High Graves’ disease
High Low Hashimoto’s disease
High TSH levels shows less amount of thyroid hormones hence causes Hashimoto’s disease.
Low TSH levels shows more amount of thyroid hormones hence cause Graves’ disease.
What if thyroid stimulating Hormone is Low?
When there is low level of Thyroid Stimulating Hormone, there may be two conditions – either the levels of T3 or T4 will be high or they may be low.
When there is low level of Thyroid Stimulating Hormone and low level of T3 and T4. Then it may cause secondary hypothyroidism. Secondary hypothyroidism is a condition in which hypothalamus and the pituitary gland fails to stimulate Thyroid Stimulating Hormone and thus, results in the decreased activity of the thyroid gland.
And when there is low level of Thyroid Stimulating Hormone and high level of T3 and T4. Then it may cause Graves’ disease. It is an autoimmune disorder. This condition is also known as hyperthyroidism.
Antibodies made by the human body acts as Thyroid Stimulating Hormone-antibodies towards the thyroid gland. This elevates the level of thyroid hormones. This results in mental fatigue, physical fatigue, weight loss, etc.
Thyroid Stimulating Hormone High Level Symptoms
High Thyroid Stimulating Hormone level or Hypothyroidism may alter variety of body functions. Body’s metabolism is the main function which has altered due to high Thyroid Stimulating Hormone.
Other symptoms of thyroid problems may vary from mild to severe. The most common symptoms include are:
- Weight gain
- Muscles and joint pain
- Hair loss
- Goiter (enlarged thyroid)
- Brittle nails
- Disturbed menstrual cycles
- Deep or hoarse voice
- Cold intolerance (inability to tolerate cold temperatures)
- Inability to think
- Dry and scaly skin
The most severe symptom of hypothyroidism is myxedema. It can lead to coma and may be fatal to the human body. The other symptoms followed by myxedema are low body temperature, problem in breathing, slow heart rate, etc.
Thyroid Stimulating Hormone Test
Several blood test are there to measure TSH, T4, free T4 and T3.
The thyroid stimulating hormone test is the easy way to detect whether thyroid gland is failing or it is due to failure of the pituitary gland or the hypothalamus. If the level of the Thyroid Stimulating Hormone is high means low level of T3 and T4. This means the thyroid gland is directly affected causing hypothyroidism.
And vice versa, with the low level of Thyroid Stimulating Hormone (TSH) means high level of T3 and T4. It indicates an individual is having overactive thyroid gland causing hyperthyroidism.
Depending only upon test should not be the only way to determine the diseases. Symptoms of thyroid problems should also be consider as important as test. One Thyroid Stimulating Hormone test in India nearly cost around Rs. 100-250.
T4 in the body circulates in two forms one is Free T4 and another one is T4. As discussed earlier, in synthesis the T4 is bound to a protein named as thyroglobulin which prevents the entry of the T4 into the tissues.
Free T4 doesn’t enter the tissues to exert its effect. This free T4 plays the major role in testing the thyroid gland functioning. Test which measures are Free T4 (FT4) and Free T4 Index (FT4I). The low levels of FT4 and FT4I signifies hypothyroidism due to the dysfunctioning of pituitary gland.
The high level of Thyroid Stimulating Hormone and low level of FT4 FT4I signifies the primary hypothyroidism due to the presence of the disease in thyroid gland. The low level of Thyroid Stimulating Hormone (TSH) and high level FT4 and FT4I signifies the hyperthyroidism.
The T3 test helps in diagnosis of hyperthyroidism and its severity. Individuals with high T3 level will be hyperthyroid. T3 test is not or rarely in diagnosis of hypothyroidism.
Thyroid Anti-body Test
The immune system of the human body makes antibodies against any foreign entrants. The antibodies formed by the blood cells also called as lymphocytes destroys the foreign entrants. These lymphocytes makes antibodies against it’s own cells of thyroid and destroys it and hence causes thyroid disease.
The immunoglobulins used in synthesis of T3 and T4, thyroid peroxidase and thyroglobulins. By measuring levels of these antibodies will help in diagnosis of hypo- and hyperthyroidism.
The presence of antibodies of thyroid peroxidase and thyroglobulins indicates the cause of autoimmune disorder. This may be hypothyroidism and hyperthyroidism.
Thyroglobulins(TG) are the proteins that are formed by cells of thyroid and also by the cancer cells of thyroid. But, this test is rarely used as it doesn’t shows the functioning of the thyroid hormones. This test is useful in case of thyroid cancer cells to examine them after the surgery for treatment.
Other test involved are non-blood tests
Radioactive iodine uptake
In the synthesis of T4 and T3 iodine uptake is the first step. The normal functioning of the thyroid hormone can be diagnosed and iodine is labelled with radioactive substances in this test.
The uptake of iodine by the thyroid gland is checked with the amount of radioactive iodine. High level of radioactive iodine uptake indicates hyperthyroidism (overactive thyroid gland). And low level of radioactive iodine uptake indicates hypothyroidism (underactive thyroid gland).
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