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Questions and Answers
What is the effect of a large amount of ingested iodine on thyroid hormone synthesis?
What is the effect of a large amount of ingested iodine on thyroid hormone synthesis?
What is the primary use of radioactive iodine (RAI) in the treatment of Grave's disease?
What is the primary use of radioactive iodine (RAI) in the treatment of Grave's disease?
What is the daily requirement of iodide for the synthesis of thyroid hormones?
What is the daily requirement of iodide for the synthesis of thyroid hormones?
What is a contraindication for radioiodine therapy?
What is a contraindication for radioiodine therapy?
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What is a side effect of lithium carbonate?
What is a side effect of lithium carbonate?
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What is the form of thyroid hormone that enters the nucleus and binds to nuclear receptor protein?
What is the form of thyroid hormone that enters the nucleus and binds to nuclear receptor protein?
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What is the therapeutic use of iodinated contrast media?
What is the therapeutic use of iodinated contrast media?
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What is the effect of thyroid hormones on metabolic rate?
What is the effect of thyroid hormones on metabolic rate?
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What is a potential long-term effect of radioiodine therapy?
What is a potential long-term effect of radioiodine therapy?
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What is the common symptom of hypothyroidism?
What is the common symptom of hypothyroidism?
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What is the treatment for hypothyroidism?
What is the treatment for hypothyroidism?
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What is the source of T3?
What is the source of T3?
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What is the half-life of T3?
What is the half-life of T3?
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What is the binding protein for thyroid hormones in the blood?
What is the binding protein for thyroid hormones in the blood?
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What is the difference in potency between the d- isomer and the l- isomer with respect to their effects on growth and development?
What is the difference in potency between the d- isomer and the l- isomer with respect to their effects on growth and development?
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What is a common side effect of thyroid hormones?
What is a common side effect of thyroid hormones?
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What is the term for the abnormal enlargement of the thyroid gland?
What is the term for the abnormal enlargement of the thyroid gland?
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What is a symptom of hyperthyroidism?
What is a symptom of hyperthyroidism?
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What is the mechanism of action of propranolol in the treatment of hyperthyroidism?
What is the mechanism of action of propranolol in the treatment of hyperthyroidism?
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What is the effect of Propylthiouracil on peripheral deiodination of T4?
What is the effect of Propylthiouracil on peripheral deiodination of T4?
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What is a disadvantage of thionamides in the treatment of hyperthyroidism?
What is a disadvantage of thionamides in the treatment of hyperthyroidism?
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Which of the following thionamides is NOT teratogenic?
Which of the following thionamides is NOT teratogenic?
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Study Notes
Thyroid Gland Hormones
- Iodide is necessary for the synthesis of thyroid hormones, and can be obtained from sources such as iodized salt, iodated bread, and dairy products, with a daily requirement of 75 micrograms (about 10g of iodized salt)
Thyroid Hormone Synthesis
- The oxidation, iodination, and coupling reactions are catalyzed by iodine or thyroid peroxidase enzyme
- Lysosomal enzymes hydrolyze thyroglobulin, releasing T4 and T3
- Most of the released T4 is converted to T3 by deiodinase enzyme in peripheral tissues
Thyroid Hormone Characteristics
- Thyroxine (T4) and triiodothyronine (T3) are the two main thyroid hormones
- T4 is more abundant in the thyroid gland, with a ratio of T4:T3 of 4:1
- T3 is more potent than T4, with a potency ratio of 3-5:1
- Both T4 and T3 are bound to thyroxine-binding globulin (TBG) in the blood, with T4 being more highly bound (99.97%) than T3 (99.5%)
- The half-life of T4 is 1 week, while that of T3 is 1 day
Mechanism of Action of Thyroid Hormones
- Thyroid hormones travel in the blood bound to TBG and are transported to target cells
- T4 is converted to T3 in target cells, and only T3 enters the nucleus and binds to nuclear receptor protein
- The hormone-receptor protein complex binds to specific response elements on DNA, leading to a direct effect on transcription
- The resulting mRNA codes for specific proteins that mediate the effects of thyroid hormones
Effects of Thyroid Hormones
- Thyroid hormones promote growth and development, and are essential for growth in childhood
- They have a calorigenic effect, increasing BMR, O2 consumption, and general metabolism, as well as CHO metabolism
- They also increase lipolysis and lipid breakdown, decrease cholesterol blood levels, and increase β-adrenergic receptors in most tissues
Disorders Affecting the Thyroid Gland
- Hypothyroidism can occur in children (cretinism) and adults (myxedema)
- Causes of hypothyroidism include surgical removal of the thyroid, thyroiditis, deficiency or excess of iodine, and pituitary or hypothalamic dysfunction
- Symptoms of hypothyroidism include cold intolerance, lethargy, constipation, slowing of mental function and motor activity, weight gain, and dry/thick skin
- Treatment of hypothyroidism involves hormone replacement therapy (HRT)
Thyroid Hormone Preparations and Clinical Uses
- Thyroid hormone preparations include thyroid USP, thyroid extract, levothyroxine sodium, liothyronine sodium, and liotrix
- Clinical uses of thyroid hormones include hypothyroidism, thyroid cancer, and weight reduction
- Side effects of thyroid hormone preparations include hyperthyroidism and allergic reactions
Hyperthyroidism
- Hyperthyroidism can be caused by Grave's disease, hyperplasia of the thyroid, and exophthalmos
- Symptoms of hyperthyroidism include heat intolerance, nervousness, fatigue, weight loss, increased bowel movements, and abnormal menses
- Treatment of hyperthyroidism includes propranolol, antithyroid drugs, and surgery
- Antithyroid drugs include thiourea derivatives (thionamides) such as methimazole, carbimazole, and propylthiouracil
- Side effects of antithyroid drugs include allergy, hepatic dysfunction, agranulocytosis, and teratogenicity
Iodine Therapy
- Iodine can be used to treat hyperthyroidism and thyroid cancer
- Iodine therapy can cause allergy and has a high relapse rate
- Radioactive iodine (RAI) can be used to treat hyperthyroidism and thyroid cancer
Lithium Carbonate
- Lithium carbonate has a similar mechanism of action to iodide
- It has a narrow therapeutic window and can cause side effects such as nausea, diarrhea, and blurred vision
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Description
This quiz covers the role of iodide in the synthesis of thyroid hormones, sources of iodide, and the process of thyroid hormone production and transportation in the body.
