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47 Cards in this Set
- Front
- Back
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3 major hormones form the thyroid gland
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T3, T4, Calcitonin
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How do drugs like Perchlorate and thiocyanate treat hyperthyroidism?
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block iodide trapping (uptake into thyroid cells) by competetively inhibiting Iodide uptake through the NIS transporter
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What is Pendred Syndrome?
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defective pendrin (Cl/I exchanger on apical membrane). leads to deafness and hypothyroidism
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How does excess iodine treat hyperthyroidism?
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inhibits proteolysis of thyroglobulin (MIT/DIT) so T3/T4 cannot enter blood stream and less iodide recycling occurs
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How does propothiouracil treat hyperthyroidism?
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inhibits TPO (thyroid peroxidase) so iodide doesn't become iodine and combine with thyroglobulin = less T3/T4 production
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What are the 2 most common thioamides used?
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propothiouracil and methimazole
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De-iodination of the outer ring of T4 leads to ...
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T3
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De-iodination of the inner ring of T4 leads to ...
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rT3 (inactive)
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Blockage of 5'-deiodinase would be helpful in treating what disorder?
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hyperthyroidism. 5'-deiodinase converts T4 into highly active T3. inhibition of deiodinase = higher rT3 levels = less thyroid action. this is done by the drug amiodarone
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How does the drug amiodarone treat hyperthyroidism?
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blocks 5'-deiodinase = less T4 converted into active T3 = more rT3 = less thyroid hormone action
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What is the Wolff-Chiakoff block?
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high doses of iodine inhibit thyroid hormone organification
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A patient has lost their Wolff-Chiakoff block. What disorder will they now have?
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hyperthyroidism. Wolff-Chiakoff block: high iodide inhibits T4/T3 production. loss of this = more T4/T3 production
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Which has a higher function Levo or Dextro thyroxine?
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L-thyroxine. D-thyroxine is only 4% activity of L-thyroxine
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Where is thyroxine absorbed in the gut?
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duodenum and ileum
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In a patient with hyperthyroidism, what happens to the half-life of T4/T3?
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decreased half-life since they are used, degraded and taken out of blood more quickly
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Why is there a lag in time between thyroxine administration and effects?
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thyroxine has to first be converted into T3, then act on intracellular receptors to up-regulate transcription and protein synthesis... this takes a while before the effects are seen and the proteins are actually in full function
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What has more receptors for T3, brain or heart?
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heart
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What has more receptors for T3, brain or spleen?
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brain
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What is cretinism?
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congenital lack of thyroid hormones (or gland) = low growth and retardation
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Half-life of T4
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7 days
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Half-life of T3
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24 hours. T4 is way longer (1 week)
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Which is more active? T3 or T4
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T3 is 10x more active than T4. but more T4 is made since is has a much longer half-life
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What is liothyronine?
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synthetic T3 drug
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What is a goitrogen?
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lower T3/T4 levels, but will increase TSH levels = goiter
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What is methimazole?
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inhibits TPO enzyme to lower T3/T4 levels
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What is stronger? Methimazole or propylthiouracil?
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Methimazole
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Usually for hyperthyroidism methimazole is given to reduce TPO activity. When would we give propylthiouracil instead?
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in pregnancy, PTU crosses the placental barrier less than methimazole
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Which thioamide has a stronger effect on inhibiting 5'-deiodinase? Propylthiouracil or Methimazole?
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propylthiouracil
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If a patient is taking large doses of iodides to treat hyperthyroidism, what additional therapy would be least helpful?
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thiocyanate. thiocyanate is a competitve inhibitor of iodide uptake, but high doses of iodide given as treatment will outcompete the thiocyanate now and it will be useless
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Why would administration of radioactive iodine and thiocyanate together be a bad treatment combination for hyperthyroidism?
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Thiocyanate competitively inhibits iodide uptake (NIS transporter). radioactive iodine depends on that transporter to get into the cell and kill the overactive thyroid cells.
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Which beta-blocker can act as a 5'-deiodinase to further help treat hyperthyroidism?
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propanolol
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What is secondary hypothyroidism?
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low T3/T4 due to low TSH or TRH (very rare)
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Decreased erythropoiesis is a characteristic of which thyroid disorder?
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hypothyroidism
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Increased alkaline phophatase is a characteristic of which thyroid disorder?
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hypothyroidism
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Osteoporosis is characteristic of which thyroid disorder?
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hyperthyroidism
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Should thyroxine be given with food?
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no, empty stomach is best because absorption of T4 is too variable with food
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Atrial fibirilation is characteristic of which thyroid disorder?
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hyperthyroidism
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Lithium therapy can lead to which thyroid disorder?
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hypothyroidism
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Estrogens have what effect on TBG?
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increase TBG
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Lower doses of warfarin are needed in a patient with a thyroid disorder, What thyroid disorder is most likely?
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hyperthyroid patients need lower doses of warfarin.
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3 major treatments for hyperthyroidism
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drugs, thyroidectomy, radioactive iodine
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If propanolol is contraindicated (by asthma), what drug can be given to control thyroid storm symptoms?
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diltiazem
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How is a thyroid storm treated?
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propanolol, potassium iodide, PTU, hydrocortisone to prevent shock
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How is thyrotoxicosis treated during pregnancy?
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PTU at small doses
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Why is prednisone/hydrocortisone given in thyrotoxicosis?
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prevent shock and acts as a 5'-de-iodinase inhibitor
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Amiodarone-induced thyrotoxicosis type 1 responds best to what drug?
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thioamides (methamizole and PTU)
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Amiodarone-induced thyrotoxicosis type 2 responds best to what drug?
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glucocorticoids
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