Podcast
Questions and Answers
Which of the following is NOT a protein involved in the synthesis of thyroid hormones?
Which of the following is NOT a protein involved in the synthesis of thyroid hormones?
What is the result of the coupling of two molecules of diiodotyrosine (DIT)?
What is the result of the coupling of two molecules of diiodotyrosine (DIT)?
Which of the following is NOT a binding protein for thyroid hormones?
Which of the following is NOT a binding protein for thyroid hormones?
What is the term for hyperthyroidism due to ingestion of exogenous thyroid hormone?
What is the term for hyperthyroidism due to ingestion of exogenous thyroid hormone?
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Which of the following is a characteristic of multinodular goiter?
Which of the following is a characteristic of multinodular goiter?
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What is the result of the coupling of mono-iodo-tyrosine (MIT) and diiodotyrosine (DIT)?
What is the result of the coupling of mono-iodo-tyrosine (MIT) and diiodotyrosine (DIT)?
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Which of the following types of thyroiditis is often associated with a viral syndrome?
Which of the following types of thyroiditis is often associated with a viral syndrome?
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Which of the following is NOT a cause of thyrotoxicosis?
Which of the following is NOT a cause of thyrotoxicosis?
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What is the term for the process of inorganic iodide binding to tyrosine residues of thyroglobulin?
What is the term for the process of inorganic iodide binding to tyrosine residues of thyroglobulin?
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Which of the following thyroid hormones is secreted solely from the thyroid?
Which of the following thyroid hormones is secreted solely from the thyroid?
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Study Notes
Thyroid Hormone Synthesis
- Thyroxine (T4) and triiodothyronine (T3) are formed within thyroglobulin, a large glycoprotein synthesized in the thyroid cell.
- Inorganic iodide is oxidized by thyroid peroxidase and covalently bound to tyrosine residues of thyroglobulin.
- Iodinated tyrosine residues combine to form iodothyronines in reactions catalyzed by thyroid peroxidase.
- Two molecules of DIT combine to form T4, and MIT and DIT join to form T3.
Thyroid Hormone Transport and Regulation
- T4 and T3 are transported by thyroid binding globulin (TBG), transthyretin, and albumin.
- Only unbound (free) thyroid hormone can diffuse into cells, elicit biologic effects, and regulate thyroid stimulating hormone (TSH) secretion from the pituitary.
Thyroid Disorders
Goiter
- In multinodular goiter, follicles with autonomous function coexist with normal or even nonfunctioning follicles.
- Thyrotoxicosis occurs when autonomous follicles generate more thyroid hormone than is required.
Thyroiditis
- Painful subacute (granulomatous or de Quervain) thyroiditis often develops after a viral syndrome.
- Painless (silent, lymphocytic, or postpartum) thyroiditis is a common cause of thyrotoxicosis.
- Its etiology is not fully understood; autoimmunity may underlie most cases.
Thyrotoxicosis
- Thyrotoxicosis factitia is hyperthyroidism due to ingestion of exogenous thyroid hormone.
- This may occur when thyroid hormone is used for inappropriate indications, excessive doses are used for accepted medical indications, there is accidental ingestion, or it is used surreptitiously.
Amiodarone-Induced Thyroid Disorders
- Amiodarone may induce thyrotoxicosis (2%–3% of patients), overt hypothyroidism (5% of patients), subclinical hypothyroidism (25% of patients), or euthyroid hyperthyroxinemia.
- Amiodarone causes a destructive thyroiditis with leakage of thyroglobulin and thyroid hormones.
- Its high iodine content (37% by weight) exacerbates thyroid dysfunction in patients with preexisting thyroid disease.
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Description
Explore the process of thyroid hormone synthesis, including the formation of thyroxine and triiodothyronine, and the regulation of thyroid hormones in the body.
