Thyroid hormones and Antithyroid drugs Flashcards

1
Q

Iodine is present in what cells in the thyroid

A

follicular epithelial cells

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2
Q

how is iodide transported into the thyroid

A

active transport via Na/I symporter

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3
Q

what inhibits iodide transport into thyroid

A
  • uncouplers of oxidative phsophorylation (lose ATP production)
  • thiocyanate
  • perchlorate
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4
Q

Iodine trapping is stimulated by what hormone

A

TSH

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5
Q

What happens to the iodine once in follicular cells? where does it enter

A
  • oxidized by thyroid peroxidase in presence of hydrogen peroxide
  • iodide forms I2
  • follicular lumen
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6
Q

What process occurs to I2 in the follicular lumen

A

organification: thyroglobulin react with I2

- forms MIT and DIT

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7
Q

how is T3 and T4 formed?

A

coupling of MIT and DIT by thyroid peroxidase

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8
Q

thyroglobulin that contains T3 and T4 are stored as what

A

colloid in lumen of follicle

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9
Q

During the release of thyroid hormone, what role does TSH play

A
  • stimulates thyroglobulin back into follicular epithelial cells
  • lysosomal enzymes digest thyroglobulin and release T3 and T4
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10
Q

what molecule inversely modulates thyroid hormone secretion

A

iodide concentration

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11
Q

what molecule inhibits thyroid hormone release

A

lithium

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12
Q

What is the predominant thyroid hormone in blood circulation

A

T4

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13
Q

What is the most potent thyroid hormone in circulation

A

T3

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14
Q

In circulation, what is T3 and T4 bound to

A

both - TBG (thyroxine binding globulin)

T4 - Transthyretin

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15
Q

what converts T4 to T3

A

5’-deiodinase

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16
Q

where is D1 isozymes of 5’-deiodinase located

A

liver
kidney
thyroid

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17
Q

D1 isozymes of 5’-deiodinase responsibilites

A
  • majority of circulating T3

- conversion of T4 to T3

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18
Q

D2 isozymes of 5’-deiodinase is expressed where

A

brain
pituitary
skeletal
cardiac

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19
Q

D2 isozymes of 5’-deiodinase role

A
  • influences intracellular T3 levels in certain tissues
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20
Q

what inhibits D1 isozymes of 5’-deiodinase

A

propylthiouracil

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21
Q

where is 5’-deiodinase highest activity

22
Q

what metabolizes thyroid hormones

23
Q

How will enzyme induces of P450 impact thyroid hormone

A
  • increases conversion of T4 to T3
24
Q

what is an autoimmune disease that is the most common cause of hypothyroidism in the U.S

A

Hashimoto’s thyroiditis

25
what is secondary hypothyroidism
pituitary hypothyroidism due to TSH deficiency
26
what is the drug of choice for thyroid supplementation? why?
Levothyroxine (T4) - T4 longer duration of action - can be taken once a day
27
What is another thyroid hormone supplementation
Liothyronine (T3)
28
oral levothyroxine is used to treat what
- hypothyrodism - suppression of TSH - Hashimoto's thyroiditis
29
IV Levothyroxine is used to treat what
- Myxedma coma ( severe hypothyroidism)
30
Levothyroxine interacts with what drugs
1. agnets that reduce thyroxine 2. agents alter thyroid binding globulin 3. agents inhibit 5'-deiodinase 4. Warfin
31
name agents that reduce thyroxine bioavailability
- Calcium carbonate - aluminum hydroxide - cholestyramine - Colesevelam
32
which hormone increase serum thyroid binding globulin
estrogen
33
What molecule decreases serum thyroid binding globulin
Glucocroticod | anabolic steroids
34
Name agents that inhibit 5'-deiodinase
propylthiouracil | amiodarone
35
what is the interaction of Levothyroxine and Warfin
- thyroxine increases anticoagulant activity
36
Adverse effects of Levothyroxine
cardiovascular: increase palpitations, tachycardia, increased blood pressure
37
What is a common cause of hyperthyroidism
Grave's disease
38
What is Grave's disease
- autoimmune disorder | - antibodies bind to thyroid follicular cell or TSH receptor increasing T4 production
39
what used to treat symptoms of inflammation only for hyperthyroidism
- NSIADS | - aspirin
40
what drugs are used to treat hyperthyroidism
- Propanolol - propylthiouracil - methimazole - radioiodine (I131)
41
radioiodine (I131) is contraindicated in who
pregnancy
42
MOA for Propylthiouracil and Methimazole
- inhibit iodide incorporation into tyrosine residues | - inhibit iodotyrosyl coupling to form iodothyronine
43
what is a specific MOA for Propylthiouracil
inhibit peripheral 5'-deiodinase (D1) conversion of T4-T3
44
what antithyroid drug is preferred during pregnancy
- Propylthiouracil
45
compare the half lives of the anti-thyroid drugs
Methimazole 6 hours | Propylthiouracil 1 hour
46
side effects of Methimzaole
agranulocytosis | aplastic anemia
47
side effect of Propylthiouracil
hepatic necrosis and nephritis
48
what is the black box warning for Propylthiouracil
- liver injury and failure
49
what is iodine-131 used for
1. hyperthyroidism 2. thyroid carcinoma 3. grave's disease
50
when is iodide used
preoperative to reduce vascularity of thyroid prior to surgery
51
who should not use iodide and why
pregnant women | - induce goiter, suppress thyroid function in fetus, induce hypothyroidism