Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
34 Cards in this Set
- Front
- Back
|
What organ is responsible for Iodine organification?
|
Thyroid peroxidase!
|
|
|
Tyrosine residues of thyroglobulin (storage form of TH) are iodinated in the gland to form what?
|
MIT(monoiodotyrosie) and DIT (diiodotyrosine)
note: T3 = MIT + DIT T4 = DIT x2 |
|
|
High levels of iodide or thyroid hormones have what effect on TSH and TRH?
|
Inhibition through negative feedback
|
|
|
What cell releases the thyroid stimulating immunoglobulins that cause an increase in TH levels in pts with Graves Disease?
|
Lymphocytes
|
|
|
High levels of iodide have what effect of TH synthesis and release?
|
inhibit synthesis and release by inhibiting iodination of tyrosine
|
|
|
What causes nontoxic hypothyroidism ?
|
lack of iodine,
|
|
|
What is the mechanism of action of TH ?
|
Enters cell => T4 converted to T3 => dimerization of steroid receptor complex => T3 activated dimers interact with DNA response elements => synthesis of RNA.
note: NO heat shock proteins! |
|
|
What are the therapeutic uses of thyroid hormones?
|
-Replacement therapy in hypothyroid individuals (myxedema)
- Pituitary TSH suppresion (thyroid carcinoma, Hashimoto's thyroiditis, diffuse non-toxic goiter) -Differential diagnosis of hyperthyroidism |
|
|
Which drug is the treatment of choice for myxedema? It is T4 converted to T3 and has a long half life?
|
Levothyroxine (Synthroid, Levoxyl, Levothroid, Tirosint, Unithroid)
|
|
|
Which drug is used in patients with myxedema that can't convert T4 to T3?
|
Liothyronine (Cytomel, Triosat)
- Triostat is given IV in hospital, Cytomel is given orally. - it is more potent, faster acting, shorter duration, more expensive. |
|
|
What is the ratio of T3:T4 in Liotrix?
|
4:1 of T4 to T3
|
|
|
Which drugs are used to manage myxedema coma?
|
IV Triostat or IV Levothyroxine
-levothyroxine is not as fast |
|
|
What converts T4 to T3 in target cells, liver, and kidneys?
|
5'deiodinase
|
|
|
What are the effects of Phenytoin, Phenobarbital, and Rifambin on overall effect of thyroid hormones?
|
DECREASE effect due to increase in cytochrome P450.
|
|
|
What is the half life of T4 and T3?
|
T4- 7 days
T3 - 1 day ( more free in plasma so it gets degraded ) |
|
|
T/F: Patients with longstanding hypothyroidism should be given lower doses of T4 because they are extremely sensitive to the effects on the heart.
|
True
|
|
|
What is the clinical use of Radioactive iodine (I131)?
|
It is used to remove the thyroid gland in thyrotoxicosis or thyroid carcinoma through beta particles given off by radioactive iodine.
- Favored in patients over 21 - Adv: no surgery, permanent, doesn't endager other tissue - Disadv: Delayed hypothyroidism so pt has to take t3/4 supplements |
|
|
What drugs inhibit thyroid hormone synthesis (not release)?
|
Thiomides -Propylthiouracil and Metimazole (Tapozole)
|
|
|
What is the mechanism of Thioamides like Propylthiouracil and Methimazole?
|
- Block thyroid peroxidase -> block iodine organification (oxidation reaction for iodinationof tyrosine residues of thyroglobulin)
- Blocks coupling of DIT and MIT (T3) -High dose PTU blocks conversion of T4 to T3 |
|
|
Why are Propylthiouracil and Methimazole NOT effective in management of thyroid storm alone?
|
Slow onset of action and equires 3-4 weeks for full effectW
|
|
|
What is the safest antuthyroid drug to administer to a pregnant woman because it is less likely to cross the placenta and enter breast milk?
|
Propylthiouracil (PTU)
|
|
|
What are the adverse side effects of Propylthiouracil and Methimazole?
|
- SEVERE IMMUNE REACTIONS SUCH AS AGRANULOCYTOSIS !
- skin rash, edema, hepatotoxicity, jaundice, nephritic, arthralgia, nausea, vomiting, drug fever |
|
|
What is the mechanism of action of Lugol's strong iodine and Saturated solution of potassium iodide (SSKI)?
|
-Inhibit BOTH organification and release of thyroid hormone
-Reduce both size and vascularity of hyperplastic thyroid (beneficial for prior to thyroidectomy) -Rapid onset (2-7 days) and transient effects (wear off so rarely given alone) |
|
|
What is the clinical use of Lugol's strong iodine and Saturated solution of potassium iodide (SSKI)?
|
-Management of "thyroid storm"
-Severe thyrotoxicosis - Surgical resection preparation |
|
|
What is the mechanism of action of Diatrizoate (Hypaque) and Ihexol (omnipaque)?
|
- Decrease conversion of T4 to T3 via 5'deiodinase in liver, kidney, and other peripheral tissue
- Inhibits thyroid hormone release through feedback inhibition |
|
|
What is the clinical use of Diatrizoate (Hypaque) and Ihexol (omnipaque)?
|
Rapid decrease in T3 levels in thyrotoxicoses or thyroid storm in Emergency situation
|
|
|
What drugs are useful in managing manifestations of thyrotoxicosis such as tachycardia?
|
B-Blockers
-note: Propranolol also inhibits 5'deiodinase |
|
|
What is the mechanism of action of Lugol's strong iodine and Saturated solution of potassium iodide (SSKI)?
|
-Inhibit BOTH organification and release of thyroid hormone
-Reduce both size and vascularity of hyperplastic thyroid (beneficial for prior to thyroidectomy) -Rapid onset (2-7 days) and transient effects (wear off so rarely given alone) |
|
|
What is the clinical use of Lugol's strong iodine and Saturated solution of potassium iodide (SSKI)?
|
-Management of "thyroid storm"
-Severe thyrotoxicosis - Surgical resection preparation |
|
|
What is the mechanism of action of Diatrizoate (Hypaque) and Ihexol (omnipaque)?
|
- Decrease conversion of T4 to T3 via 5'deiodinase in liver, kidney, and other peripheral tissue
- Inhibits thyroid hormone release through feedback inhibition |
|
|
What is the clinical use of Diatrizoate (Hypaque) and Ihexol (omnipaque)?
|
Rapid decrease in T3 levels in thyrotoxicoses or thyroid storm in Emergency situation
|
|
|
What drugs are useful in managing manifestations of thyrotoxicosis such as tachycardia?
|
B-Blockers
-note: Propranolol also inhibits 5'deiodinase (t4->t3) |
|
|
If Beta-Blockers are contraindicated, that is used to manage manifestation of thyroid storm?
|
Calcium channel blockers - Diltiazem (Cardizem)
|
|
|
What is the therapy indicated for a patient with "thyroid storm" ?
|
-Proponolol or Diliazem to control manifestations
- SSKI or Lugol's to inhibit release - PTU or Methimazole to inhibit synthesis - Supportive - cool patient down. |
