Thyroid disorders are major endocrine disorders and affect vast majority of organs.If not treated it can cause serious health problems.lets find out what are the causes of hyperthyroidism in this article.
Introduction to thyroid disorders.
- The thyroid gland is a small butterfly-shaped gland located in the front of the neck.
- It has 2 lobes and both are joined together with isthmus.
- It produces tetraiodothyronine (T4) and triiodothyronine (T3) hormones.
- These thyroid hormones controls how cells of the body uses energy and regulates the body’s metabolism.
Regulation of Thyroid hormones:
- It all starts in hypothalamus.Which is situated deep in brain (The master of all actions and reactions).
- hypothalamus releases TRH that is Thyrotropin releasing hormone, this hormone then acts on pituitary gland present just below hypothalamus.
- In response to TRH pituitary gland releases TSH that is Thyroid stimulating hormone.
- As the name suggests Thyroid stimulating hormone,stimulates thyroid and Thyroid gland releases thyroxine hormone (T3 ,T4 )
- This hormones act on various parts of body and produce their actions.
How thyroid hormone is formed?
The key ingredient for the formation of thyroid hormone is iodine.
Steps in thyroid hormone formation are:
- Iodide trapping – iodide which the body acquires from the diet is transported into the thyroid follicle through the Na+/I− symporter which transports 2 ions of sodium and 1 ion of iodide across the basement membrane of the follicular cells.
- Oxidation – 2 iodide molecules are oxidized to iodine with the help of enzyme called thyroperoxidase (TPO).
I+ + I– ——————————–> I2
- Conjugation – the iodine binds to the tyrosyl residues of the thyroglobulin with the help of thyroperoxidase.
When 1 iodine molecule conjugate with thyroglobulin it forms monoiodotyrosine (MIT) and when 2 iodine molecules conjugate with thyroglobulin it forms diiodotyrosine (DIT).
I2 + tyrosyl residues of the thyroglobulin—————-> MIT
(2x I2 ) + tyrosyl residues of the thyroglobulin—————-> DIT
- Coupling reaction – when a monoiodotyrosine (MIT) is linked with diiodotyrosine (DIT) it produces T3.
When 2 moieties of diiodotyrosine (DIT) are linked they form T4.
Both T3 and T4 are secreted in blood.
MIT +DIT—————–> T3
DIT +DIT—————–> T4
Hyperthyroidism vs hypothyroidism
- Hyperthyroid-Hyperthyroidism occurs when the thyroid gland is overactive and produces increased amount of thyroid hormone.
- Person with hyperthyroid has high metabolic rate and is usually skinny and susceptible to hot climate.
- Hypothyroid-Hypothyroidism occurs when the thyroid gland is not producing enough thyroid hormone.
- Person with hypothyroid has low metabolic rate and is usually obese,lethargic and susceptible to cold climate.
- Hyperthyroidism is a condition of thyroid in which there is excessive production T4 and T3 hormones.
- This is also known as overactive thyroid gland.
What are Causes of hyperthyroidism
Graves' disease a major causes of hyperthyroidism
- Graves’ disease is the most common cause of hyperthyroidism.
- It is an autoimmune disorder which means that the immune system of our body will attack the thyroid gland.
- Thyroid gland is now not able to respond to the thyroid stimulating hormone (TSH) normally and result in increase in the formation of thyroid hormone.
- Thyroiditis is inflammation of the thyroid gland.
- As there is inflammation there patient will have fever and sore throat with painful swallowing.
- Sometimes there may be pain in the neck and thyroid gland tenderness
- Thyroiditis causes the stored thyroid hormone to leak out from the gland.
- This thyroid hormone enters the blood.
- Different types of thyroiditis which can cause hyperthyroidism are:
- Subacute thyroiditis- This condition is said to be caused by viruses. In this there occurs inflammation to the body.
- Postpartum thyroiditis-thyroiditis which is caused in a pregnant female after she gives birth to healthy child. This type of thyroiditis is also called as lymphocytic thyroiditis as there occur lymphocytic (white blood cell) accumulation in the gland.
- Silent thyroiditis-it is said to be an auto immune diseases. Therefore it is painless
- So in these patient there occurs a phase of hyperthyroidism which may last for up to 3 months and is often followed by a phase of hypothyroidism which usually lasts for 12 to 18 months and majority of people return back to normal state.
Overactive thyroid nodules/ toxic multinodular goiter-commonly seen causes of hyperthyroidism
- Thyroid nodules is a benign condition, where in there occurs either single or multiple nodules in the thyroid gland.
- These thyroid nodules usually do not produce thyroid hormone.
- In some cases these nodules may become overactive and produce thyroid hormone independently.
- If there is only one overactive nodule it is called a single functioning goiter.
- When many thyroid nodules became overactive it is called as toxic multinodular goiter.
Increased intake of thyroid hormones is also listed in causes of hyperthroidism.
- High amount of thyroid hormone intake is very common.
- When a person is prescribed thyroid hormone, he should take it regularly and follow up with as instructed by the doctor.
- This is because the dose of thyroid required by the body might change.
- To keep track of these changes and to adjust dose accordingly routine blood test and follow up is necessary.
- In case if a person takes too much of thyroid hormone for long time he may end up getting hyperthyroidism.
Excessive iodine intake
- Thyroid gland uses the iodine in our body to make the thyroid hormone.
- Increase or decrease of iodine in the body, signals the thyroid gland to increase or decrease the production of thyroid hormone respectively.
- Excessive intake of iodine in diet or iodine supplements causes the thyroid gland to become overactive and causes hyperthyroidism.
- Example amiodarone is a drug used in the treatment of heart problems, it contains a lot of iodine and may result in thyroid function abnormalities.
Pituitary gland tumor
- Normally the pituitary gland secretes a hormone called TSH (thyroid stimulating hormone).
- This hormone as the name suggests acts on the thyroid gland causing it to produce thyroid hormone.
- A pituitary gland tumor may lead to excess production and secretion of TSH.
- This will cause the thyroid gland to produce an abnormally high amount of thyroid hormone.
- Eventually it will result in hyperthyroidism.
- Other tumors which can causes hyperthyroidism are: thyroid tumors, tumors of the ovaries or testes, gestational trophoblastic neoplasm.
- tumors or space occupying lesions in brain around pituitary may compress pituitary gland and there maybe defective TSH secretion leading to thyroid disorders.
Other uncommon causes of hyperthyroidism
• Neonatal hyperthyroidism
Graves disease is the most common cause of hyperthyroidism.
If a female with graves disease or a female who was once in the past treated for graves disease gets pregnant, there is a possibility that her baby may have hyperthyroidism.
Neonatal hyperthyroidism signs are:
- – Low birth weight
- – Small head circumference
- – Thyroid gland enlargement
- – Frequent passage of stool
• Hyperemesis gravidarum
- Hyperemesis gravidarum is a condition seen in pregnant female.
- It is characterized by excessive nausea and vomiting in early pregnancy.
- Some patient with hyperemesis gravidarum might develop hyperthyroidism as they have a mildly elevated thyroid hormone level.
• Hashimotos thyroiditis
- Hashimotos thyroiditis is an autoimmune condition where in the immune cells attack the thyroid gland and causes hypothyroidism.
- In a very rare scenario the patient might initially have hyperthyroid and then become hypothyroid.
It is thought that even genetics can play a role in causing hyperthyroidism.
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