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44 Cards in this Set
- Front
- Back
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Primary hypothyroidism?
Secondary? Tertiary? |
malfunction of the thyroid itself
not enough TSH from pituitary not enough TRH from hypothal |
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most severe form of hypothyroidism?
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myxedema (accumulation of MPS and water in dermis --> puffy skin)
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What is the most common cause of hypothyroidism in US?
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Hashimoto's thyroiditis
AB atttack thyroglobulin, thyroperoxidase, or TSH receptor |
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What is thyroglobulin?
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contains activated tyrosine molecules that get joined by enzymes to make MIT and DIT
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How is iodine taken up?
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it accumulates in thyroid
transports by energy dependent process up a gradient using a Na-I Symporter (this last step can be regulated by drugs) |
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What happens to I once it is taken up?
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oxidized by H2O2 and TPO
Enzyme joins activated iodine atoms to activated tyrosines of thyroglobulin --> MIT and DIT TPO couples MIT and DIt --> T3 and DIT x2 --> T4 |
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What can inhibit TRH
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Somatostatin (SST)
DA GC's |
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Waht things in diet can --> Hashimoto's thyroiditis?
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Lack of I2 in diet, remedied with iodized salt
Cabbage Soybeans Sphiach can interfere with thyroid hormone production |
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What do goitrogens do? Examples?
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block T2/T4 release
cabage can do this |
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What other conditions are associated with severe iodide deficiency?
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cretinism
dwarfism congenital hypothyroidism |
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What chemicals may induce hypothyroidism?
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iodides
lithium fluiroide thioamides aminosalicylic acid phenylbutazone amiodarone |
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What happens with amiodorone metabolism?
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elevates serum i levels
They rise enough to inhibit thyroid hormone production Inhibits T4 --> T3 conversion Metabolites block binding of T2 to receptors |
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What effect does pregnancy have on thyroid function?
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--> increased TBG during pregnancy --> hypothyroid state that resolves after birth
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Treatments of hypothyroidism?
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synthetic thyroxine (levothyroxine/L-T4)
Liothyronine T3 |
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Does levothyroxine or liothyronine have longer half-life?
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levothyroxine (7 d)
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Does levothyroxine or liothyronine have more adverse effects?
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liothyronine (cardiotoxicity)
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Effects of T3/T4 overdose?
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signs of hyperthyroidism
increased Ca loss --> increased risk for osteoporosis |
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How is hypothyroidism treated in pregnancy?
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levothroxine is given (it is identical to natural T4)
Dose might have to be increaed |
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Which is the most common cause of hyperthyroidism?
Pathophysiology |
Graves' disease
AB that cross-react with human TSH receptors |
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What causes the exopthalmos seen in hyperthyroidism?
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autoAB activation of TSH-R on orbital fibroblasts --> hyaluronic acid production --
> increased osmotic load of tissues --> passive swelling |
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What is the 2nd most common cause of hyperthyroidism?
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toxic nodular goiter (no exopthalmos)
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What happens in thyroid adenoma, clinically?
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cancerous cells in thyroid gland that overproduce thyroid hormones
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Amiodarone and hyperthyroidism?
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structurally similar to T4, plus it has high I content
Can cause hypothyroidism when serum I levels are too high and suppress TSH secretion Cause hyperthyrodism when it brings I levels up to a more normal level |
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4 types of drugs used to treat hyperthyroism?
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drugs taht modify production of thyroid hormone
drugs that block I uptake drugs that modify tissue response drugs that destroy the thyroid gland |
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Basic mechanims of thioamides
Drugs in this category? |
modify the production ofo thyroid hormone
They bind TPO competitively and inhibit I incorporation and coupling PTU methimazole carbimazole |
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What is the main difference between PTU and the other thioamides?
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Inhibits 5 deiodinase and therefore reduces T4 --> T3 conversion
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Which thioamide has the longest half life?
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Methimazole (given once a day, 6-8 hr half life)
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Which thioamide is good in pregnancy?
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PTU (more strongly bound to proteins)
Thioamide can penetrate the placental barrier |
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Adverse effects of thioamides?
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rash
HA nausea pain jaundice agranulocytosis can occur rarely |
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basic mechanism of anion inhibitors?
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block I uptake
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Which are the anion inhibitors
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perchlorate
thiocyanate pertechnetate |
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how do anion inhibitors work?
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they compete withe I for NIS
can displace I alrady taken up by cell |
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what is major use of anion inhibitors?
adverse effects? |
to block I uptake in amiodarone induced hyperthyrodism
anemia |
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Which is the preferred hyperthyroidism treatment for pts over 21 yo?
what may be required if pt is elderly? |
radioiodide
pretreatment wiht methimazole |
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what results from radioidide?
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hypothyroidism
wht lifelong levothyroxine replacement possibly needed |
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Actions of I
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inhibition of thyroperoxidase, colloid resorption, proteolysis
hyperthyroid sx subside in 1-2 dyas, and 10-14 d for peak effect |
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cons of I?
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leaves thyroid loaded with I which is problematic for I and thioamide tx to follwo
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when is I given?
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reduces size and vascularity of thyroid before thyroidectomy (given as KI)
thyrotoxic crisis when hormone production must be stopped immediately |
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adverse efects of I
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sore throat
rash ulcers of mucous membranes metallic taste can cause fetal goiter |
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What can block T4-->T3?
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iodinate contrasting aents
dexamethasone beta-blockers PTU |
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What is guanethidine?
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norE blocking agen used in eye to ameliorate exopthalmos
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Thyroid storm?
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thyrotoxic crisis caused by hyperthyroidism wiht a precipitating factor (infectioin, etc)
--> sudden exacerbation of all sx of thyrotoxicosis (life threatening) |
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treatment of thyroid storm?
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Beta blockers to control CV probs and block T4-->T3
PTU to block synth of new hormone and T4-->T3 KI to block proteolysis of TG Dexamethasone to protect against shock and prevent T4-->T3 Iodinated contrast to block T4-->T3 supportive therapy |
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what should be avoided in thyroid storm?
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aspirin
can increase free T4 and T3 |
