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90 Cards in this Set
- Front
- Back
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What is the daily adult iodide intake?
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The daily adult iodide intake is 150 mcg
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How much does the thyroid uptake from the extracellular fluid pool?
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75 mcg
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What anions are able to inhibit the sodium/iodide symporter?
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Thiocyanate, pertechnetate, and perchlorate
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What is the transport system to move iodide into the follicle?
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The transport of iodide into the thyroid gland by an intrinsic follicle cell basement membrane protein called the sodium/iodide symporter
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What is Pendred's syndrome?
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A syndrome of deafness and goiter due to absence or deficient pendrin
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Where is pendrin located?
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At the apical cell membrane,
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What is pendrin
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A second I- transport enzyme that controls the flow of iodide
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What is iodide organification?
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The process of iodide being oxidized to iodine by thyroidal peroxidase then rapidly iodinating tyrosine residues within the thyroglobulin molecule
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What conditions are able to block thyroidal peroxidase?
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Thyroidal perioxidase is transiently blocked by high levels of intrathyroidal iodide and blocked more persistently by thioamide drugs
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How are thyroxine, T3, MIT, DIT released from thyroglobulin?
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Thyroxine, T3, MIT, DIT are released from thyroglobulinby exocytosis and proteolysis of thyroglobulin at the apical colloid border
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How does high intrathyroidal iodide block the release of T3 and T4?
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Thyroidal peroxidase is transiently blocked and the process of proteolysis of thyroglobulin is also blocked
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What is the half life of T4 vs T3?
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T4 has a half life of 7 days
T3 has a half life of 1 day |
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What drugs are responsible for the inhibiting the 5' - deiodinase necessary for the conversion of T4?
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Amiodarone, iodinated contrast media, beta blockers, and corticosteriods
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How is reverse T3 formed?
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By the monodeiodination of the inner ring of T4
3,3',5' - triiodothyronine |
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How is T3 formed from T4?
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Deiodination of T4
Monodeiodination of the outer ring, making 3,5,5' - triiodothyronine (T3) |
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Which one has higher oral absorption?
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80% of T4
95% of T3 |
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How does TSH stimulate the thyroid cell?
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TSH stimulates an adenylyl cyclase - mediated mechanism in the thyroid cell to increase the synthesis and release of T4 and T3
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How doe the thyroid gland regulate the uptake of iodide and thyroid hormone synthesis
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The mechanism is related to the iodide level in the blood
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What is Wolff - Chaikoff block?
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Large doses of iodine that inhibit iodide organification
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In Graves' disease, what is the mechanism for hyperstimulating the thyroid?
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In Graves' disease, lymphocytes secrete a TSH receptor -stimulating antibody (TSI). TSI binds to the TSH receptor and stimulates the gland like TSH but the duration of its effect is much longer
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The naturally occuring thyroid molecules are _______ isomers
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levo (L) isomers
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Where is thyroxine absorbed best?
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In the duodenum and ileum
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What conditions absorb T3 and T4 absorption?
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Severe myxedema with ileus
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How is thyroid metabolism altered in pregnancy, oral contraceptives, and estrogen administration?
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TBG sites are increased so there is an initial shift of hormone from free to bound state and there is a decrease in elimination until the normal hormone concentration
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What mediates the effects of thyroid hormone on metabolic processes?
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The activation of nuclear receptors that lead to increased formation of RNA and subsequent protein synthesis
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How does starvation affect thyroid hormone?
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Starvation lowers both circulating T3 hormone and cellular T3 receptors
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What is congenital cretinism?
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Thyroid deprivation in early life results in irreversible mental retardation and dwarfism
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Why is T3 not recommended for hormone replacement?
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It has a shorter half- life (24 hours) which requires multiple daily doses; higher cost; the greater difficulty of monitoring its adequacy of replacement
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What drugs are responsible for the decreasing TBG?
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Androgens, glucocorticoids
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Hyperthyroidism requires _____ doses of warfarin and hypothyroidism requires _____ doses of warfarin
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Lower
Higher |
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Do you get impaired insulin action and glucose disposal in hypo- or hyperthyroidism?
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Hypothyroidism
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Which is best for the short-term suppression of TSH (T3 or T4)?
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T3
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How do goitrogens work?
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Goitrogens are agents that suppress secretion of T3 and T4 to subnormal levels and thereby increase TSH --> glandular enlargement of Thyroid
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Which has the highest potency?
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Methimazole is about 10 x more potent than PTU
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Why is propylthiouracil preferable in pregnancy?
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PTU is more strongly bound to protein and crosses the placenta less readily
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What class are the thioamides in pregancy?
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Both thioamides cross the placental barrier and are concentrated in the fetal thyroid.
Pregnancy category D |
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How do the thioamides block uptake of iodine?
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They don't block uptake of iodide by the gland
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What is the mechanism of action for the thioamides?
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The major acgtion is to prevent hormone synthesis by inhibiting the thyroid peroxidase -catalyzed reactions and blocking iodine organification
They also block coupling of the iodotyrosines |
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Why do PTU and methimazole work so slowly?
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It is because synthesis rather than the release of hormones is affected, --> onset is slow ( about 3-4 weeks) before the stores for T4 are depleted
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Which patients are at most risk for agranulocytosis?
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The risk may be increased in elderly patients and in those recieving high- dose methimazole therapy
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How do the monovalent anions like perchlorate, pertechnate, and thiocynate work to block uptake of iodide?
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They block via competitiive inhibition of the iodide transport
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What is the main indication for using a monovalent anion in hyperthyroidism?
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The major clinical use for potassium perchlorate is to block thyroidal reuptake of I- in patients with iodide- induced hyperthyroidism
i.e. amiodarone -induced hyperthyroidism |
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What is the type of radioactive iodine used for treatment of thyrotoxicosis?
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131 I is the only isotope used for treatment of thyrotoxicosis
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What are the actions of iodides on the thyroid?
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Iodides inhibit organification and hormone release and decrease the size and vascularity of the hyperplastic gland.
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How do propanolol affect thyroid levels?
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Propranolol at doses greater than 160 mg/d may also reduce T3 levels approximately 20% by inhibiting the peripheral conversion of T4 to T3
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How do the iodides prepare the thyroid the surgery?
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Iodides decrease the vascularity, size, and fragility of a hyperplastic gland
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What are the liver effects of the thioamides?
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Hepatitis is common with PTU, cholestatic jaundice is common with methimazole
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How does radioactive iodine treat thyrotoxicosis?
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It emits beta rays which destroy of the thyroid parenchyma
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What is the most common cause of hypothyroidism?
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The most common cause of hypothyroidism is Hashimoto's thyroiditis
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What is the average of thyroxine for an adult
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1.7 mcg/kg/d
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How long does it take after a given dose of thyroxine to reach steady state.
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6-8 weeks
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What is the optimal range to maintain the TSH?
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0.5- 2.5 mU/L
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What are the signs of thyroxine toxicity in children?
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restlessness
insomnia accelerated bone maturation and growth |
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What are the signs of thyroxine toxicity in adults?
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increased nervousness
heat intolerance episodes of palpitation and tachycardia or unexplained weight loss |
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What is the treatment regimen for patients with underlying cardiac disease?
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Start levothyroxine in a dosage of 12.5 -25 mcg/d for 2 weeks, increasing the dosasge by 25 mcg every 2 weeks until euthyroid
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Why do we cautiously correct hypothyroid in a patient with coronary artery disease?
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The low levels of circulating thyroid hormone actually protect the heart against increasing demands that could result in angina pectoris or MI
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What are some signs of a patient with myxedema coma?
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Progressive weakness
Stupor Hypothermia Hypoglycemia Hypoventilation Hyponatremia water intoxication shock death |
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Why do myxedema coma patients require a large loading dose of levothyroxine?
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These patients have large pools of empty T3 and T4 binding sites that must be filled before there is adequate free thyroxine to affect tissue metabolism
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In many hypothyroid pregnant patients, an _____ in the thyroxine dose is needed to normalize the serum TSH
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increase of about 30-50%
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What is the definition of subclinical hypothyroidism?
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An elevated TSH level and normal thyroid hormone level
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When should hormone therapy be started in a subclinical hypothyroid patient?
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For patients with TSH levels greater than 10 mIU/L
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What is the most common form of hyperthyroidism?
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Graves' disease
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How does PTU lower the level of activated thyroid hormone?
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PTU inhibits the conversion of T4 to T3, so it brings the level of activated thyroid hormone more quickly than methimazole
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What is the best clinical guide to remission in hyperthyroidism?
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Reduction in the size of the goiter
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What are the three options for treating hyperthyroidism?
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1. Antithyroid drug therapy
2. Surgical thyroidectomy 3 Destruction of the gland |
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What is the treatment of choice for patients with multinodular goiters/
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A near-total thyroidectomy
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Why should iodide not be used alone?
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Iodide should not be used alone, because the gland will escape from the iodide block in 2- 8 weeks and it withdrawal may produce severe exacerbation of thyrotoxicosis in an iodine -enriched gland
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When should you expect to see shrinkage of the thyroid gland after radioiodine?
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6 -12 weeks
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What should be done before sub-total or near total thyroidectomy?
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Treatment with antithyroid drugs until euthyroid and about 10-14 days prior to surgery take potassium iodide
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What non-thyroid hormone medications are helpful in treating the symptoms of hyperthyroid.
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Propanolol is useful in controlling tachycardia, HTN, Afib
Dilitiazem can be used where B blockers contraindicated |
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What is the primary diagnostic test for thyroid neoplasms?
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Fine needle aspiration biopsy and cytologic examination
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What is the management of thyroid carcinoma?
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Total thyroidectomy , postoperative radioiodine therapy, and lifetime replacement with levothyroxine
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How do you evaluate for recurrence for some thyroid malignancies?
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Withdrawal of thyroxine replacement for 4-6 to cause TSH rise
There is tumor recurrence if there is a rise in serum thyroglobulin or postive I 131 scan |
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What is nontoxic goiter?
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A syndrome of thyroid enlargement without excessive thyroid hormone production.
This is due to TSH stimulation from inadequate thyroid hormone synthesis |
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what is the most common cause of nontoxic goiter worldwide?what about the USA
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Iodide deficiency
Hashimoto's thyroiditis |
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What is the optimal iodide intake?
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150-200 mcg
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What is the difference between amiodarone- induced thyrotoxicosis type I and II?
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Type I is iodine-induced occurs in persons with underlying thyroid disease i.e. multinodular goiter
Type II is inflammatory thyroiditis occurs in patients with thryoid disease due to leakage of thyroid hormone into the circulation |
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What is the difference between the treatment of amiodarone- induced thyrotoxicosis type I and II?
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Treatment of type I requires therapy with thioamides while type II responds to glucocorticoids
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What is subclinical hyperthyroidism?
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Subclinical hyperthyroidism is defined as a suppressed TSH level with conjunction with normal thyroid hormone levels
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When should you treat subclinical hyperthyroidism?
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Hyperthyroidism is appropriate in those with TSH less than 0.1 mIU
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What is the mechanism for infant Graves' disease?
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Graves disease may occur either due to passage of maternal TSH-R ab through the placenta, stimulating the thyroid gland of the neonate or to genetic transmission of the trait to the fetus
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Compare the laboratory studies In a newborn with Graves disease vs a normal infant.
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Elevated free T4, markedly elevated T3, and low TSH in an infant with Graves disease
In a newborn, the TSH is elevated at birth |
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How are glucocorticoids useful in hyperthyroidism?
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They block the conversion of T4 to T3
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What is the treatment for neonatal Graves' disease?
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PTU, Lugol's solution (iodide), propanolol
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If the neonatal Grave's disease is caused by maternal antibodies, what is the prognosis?
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The disease is usually self-limited and subsides over a period of 4-12 weeks
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What is the cause of subacute thyroiditis?
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During the acute phase of a viral infection of the thyroid gland, there is destruction of thyroid parenchyma with transient release of stored thyroid hormones
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What is the treatment of subacute thyroiditis?
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Supportive therapy
Beta blocker for tachycardia ASA or NSAIDs to control local pain and fever Cortisteriods in severe cases for inflammation |
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What is thyroid storm?
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A sudden acute exacerbation of all symptoms of thyrotoxicosis
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How do you treat thyroid storm?
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Propanolol or Diltiazem
PTU Potassium iodide Hydrocortisone |
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when can a pregnant patient get a subtotal thyroidectomy?
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in the 2nd trimester
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