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21 Cards in this Set
- Front
- Back
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Triiodothyronine/ tetraiodothyronine (thyroxine)
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T3/ T4
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If iodide intake is increased, the thyroid responds how?
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the fractional iodine uptake by the thyroid is diminished as iodide uptake is increased.
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What is the main transporter of iodide into the thyroid gland by an intrinsic follicle via the basement membrane?
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Sodium/iodide symporter (NIS)
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What transport enzyme controls I- through the apical membrane?
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Pendrin. Pendred's syndrome causes hypothyroidism and congenital deafness.
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What enzyme converts I- to iodine?
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thyroidal peroxidase
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Process in which MIT and DIT are formed?
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Iodide organification: iodinates tyrosine residues within the thyroglobulin molecule
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What processes are blocked by high levels of Iodides? (2)
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1. Thyroidal peroxidase linking iodine to thyroglobulin (Wolff-Chaikoff block)
2. Proteolysis ( creating sole T4, T3) |
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What inhibits 5'deiodinase to convert T4 -> T3?
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amiodarone, iodinated contrast media, Beta blockers, and corticosteroids, severe illness
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What GPCR does ACTH activate?
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Adenylyl cyclase- GS(Alpha)
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drugs that increase metabolism of T4 & T3
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rifampin, phenobarbital carbamazepine, phenytoin, tyrosine kinase inhibitors, HIV protease inhibitor
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Levothyroxine (Levoxyl, Synthroid)
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T4- Activation of nuclear receptor, maximum effect seen 6-8 weeks of therapy
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Liothyronine (Cytomel)
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T3- Activation of nuclear receptor, maximum effect seen 6-8 weeks of therapy
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Methimazole
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(thioamide) inhibits thyroid peroxidase (No organification, no peripheral deiodination)
Methimazole is preferred to PTU.... Except(?) (carbimazole -> methimazole) Crosses placental barrier |
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Toxic side effect of thioamides?
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Agranulocytosis.
PTU is counter indicated in hepatitis |
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Propylthiouracil (PTU)
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(Thioamide) inhibits thyroid peroxidase (No organification, no peripheral deiodination)
Preferred during pregnancy or thyroid storm |
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Lugol solution/ Potassium iodide
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inhibits oranification. Used to reduce the size and vascularity of gland before surgery.
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Propranolol
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inhibition of Beta adrenoreceptors,
inhibits conversion of T4-> T3. *Use in Thyroid storm* control tachycardia, hypertension, and atrial fibrillation |
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Diltiazem
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Ca2+ blocker, used to control tachycardia for thyroid storm in patients where Propranolol is contrainidcated (asthmatics)
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radioactive iodine
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Patients should be euthyroid or on Beta blockers before before RAI
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Why can thyroxine be taken orally?
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It is a peptide therefore it is readily absorbed
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Amiodarone
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Anti-arrhthymic, inihibits conversion of T4-> T3
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