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Thyroid Physiology and Disorders
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1
Question
What are the two primary thyroid hormones produced by the gland?
Answer
Triiodothyronine (T3) and thyroxine (T4)
2
Question
Name one major function of thyroid hormones.
Answer
Regulate growth and development (calorigenesis, metabolism)
3
Question
Which protein is mainly responsible for transporting thyroid hormone in plasma?
Answer
Thyroxine-binding globulin (TBG)
4
Question
What enzyme catalyzes iodide organification in the thyroid?
Answer
Thyroidal peroxidase
5
Question
What are MIT and DIT the precursors of?
Answer
Monoiodotyrosine and diiodotyrosine, precursors to T3 and T4
6
Question
What process releases T3 and T4 from thyroglobulin?
Answer
Proteolytic cleavage/s proteolysis in the thyroid
7
Question
What enzyme is primarily responsible for peripheral conversion of T4 to T3?
Answer
Deiodinase
8
Question
What is reverse T3 (rT3)?
Answer
An inactive product from inner-ring deiodination of T4
9
Question
Which plasma protein largely binds thyroid hormone in circulation?
Answer
Thyroxine-binding globulin (TBG)
10
Question
Where does most peripheral generation of T3 occur?
Answer
Liver and kidney (sites of deiodination)
11
Question
What is the clinical syndrome of overexposure to thyroid hormone called?
Answer
Hyperthyroidism (thyrotoxicosis)
12
Question
Name a common cause of secondary hypothyroidism.
Answer
Pituitary disorder inhibiting TSH secretion
13
Question
Name a common cause of tertiary hypothyroidism.
Answer
Hypothalamic inability to release TRH
14
Question
What condition is characterized by autoimmune destruction of the thyroid?
Answer
Hashimoto’s thyroiditis
15
Question
What is goiter?
Answer
Enlargement of the thyroid gland
16
Question
What compounds inhibit iodide uptake by the thyroid gland?
Answer
Anions such as perchlorate and thiocyanate
17
Question
What is the major clinical use of potassium perchlorate today?
Answer
Block thyroidal reuptake of iodide in iodide-induced hyperthyroidism
18
Question
What is the historical role of iodides in thyroid treatment?
Answer
Former major antithyroid agents that inhibit organification and release
19
Question
What adverse effect is the most dangerous with thioamide antithyroid drugs?
Answer
Agranulocytosis
20
Question
Which thioamide is more potent: methimazole or propylthiouracil?
Answer
Methimazole (about ten times more potent)
21
Question
Which thioamide has a shorter plasma half-life, propylthiouracil or methimazole?
Answer
Propylthiouracil (1.5 hours)
22
Question
Why are thioamides given with caution in pregnancy?
Answer
They cross the placental barrier and can affect the fetal thyroid
23
Question
What is the primary mechanism of thioamides’ antithyroid action?
Answer
Inhibition of thyroid peroxidase and iodine organification
24
Question
What major adverse hematologic reaction can thioamides cause?
Answer
Agranulocytosis
25
Question
What is the role of iodides when used with thioamides in therapy?
Answer
Delay onset of thioamide effect and reduce vascularity of gland
26
Question
Why should iodides not be used alone for thyrotoxicosis?
Answer
Gland escapes block after 2–8 weeks; risk of rebound thyrotoxicosis
27
Question
What is Jod-Basedow phenomenon?
Answer
Iodide-induced hyperthyroidism
28
Question
What is a key effect of iodinated contrast media on thyroid hormones?
Answer
Inhibit conversion of T4 to T3 in multiple tissues
29
Question
What isotope is used for treatment of thyrotoxicosis?
Answer
Sodium iodide-131 (131I)
30
Question
What surgical option is preferred for very large goiters?
Answer
Near-total thyroidectomy