Thyroid-valentovic

Question 1

Iodide uptake

Answer 1

Active transport of iodide into thyroid follicular epithelial cells occurs via the Na/I symporter

Question 2

Iodide uptake

Inhibited by

Answer 2

Uncouplers of oxidative phosphorylation (lose ATP) production)

Thiocyanate and perchlorate

Question 3

Iodide trapping stimulated by…

Answer 3

TSH

Question 4

Iodide concentration and thyroid hormone secretion

Answer 4

Iodide concentration inversely modulates thyroid hormone secretion

Question 5

Thyroid hormone release is inhibited by…

Answer 5

Lithium

Question 6

Which Thyroid hormone(s) is/are released into circulation

Answer 6

T3 and T4

Question 7

How are T4 and T3 transported

Answer 7

Bound to thyroxine binding globulin (TBG)

T4 also by transthyretin

Question 8

What is the predominant hormone in the blood?

Answer 8

T4!!!!!!

IMPORTANT

Question 9

What is the most active thyroid hormone?

Answer 9

T3 (5x more active than T4)

IMPORTANT

Question 10

T3 peripheral formation

Answer 10

T4 deiodinated to T3 by iodothyronine 5-deiodinase (3 isoenzymes)

Question 11

Isozymes of iodothyronine 5-deiodinase

D1

Where is it expressed?

Answer 11

Liver, kidney, and thyroid

Question 12

Isozymes of iodothyronine 5-deiodinase

D1

What is its function?

Answer 12

Conversion of T4 to T3

Responsible for majority of circulating T3

Question 13

Isozymes of iodothyronine 5-deiodinase

D1

What is it inhibited by?

Answer 13

Propylthiouracil

Question 14

Isozymes of iodothyronine 5-deiodinase

D2

Where is it expressed?

Answer 14

Brain, pituitary, skeletal and cardiac mm

Question 15

Isozymes of iodothyronine 5-deiodinase

D2

Function

Answer 15

Influences intracellular T3 levels in these tissues

Question 16

Isozymes of iodothyronine 5-deiodinase

D2

What is it inhibited by?

Answer 16

Unresponsive to propylthiouracil

Question 17

Where is 5-deiodinase activity highest?

Answer 17

Liver

Question 18

Thyroid hormone metabolism

Answer 18

Metabolized by P450

ENZYME INDUCERS WILL INCREASE CONVERSION OF T4 TO T3

Question 19

Primary hypothyroidism

Define

Answer 19

Diminished thyroid hormone production and high TSH levels

Question 20

Primary hypothyroidism

Causes

Answer 20

Hypothyroidism

Chronic autoimmune thyroiditis or Hashimoto’s thyroiditis (MC)

Thyroid damage due to rx with radioactive iodine

Surgical removal of thyroid

Question 21

Secondary hypothyroidism

Define

Answer 21

Pituitary hypothyroidism: due to TSH deficiency

Question 22

Thyroid hormone supplementation

What is DOC?

Answer 22

Levothroxine (T4)

Question 23

Thyroid hormone supplementation

Why is liothyronine (T3) not DOC?

Answer 23

Shorter half-life, greater variability

Question 24

Thyroid hormone supplementation

When can liothyronine (T3) be used?

Answer 24

Individuals with 5 deiodinase deficiency

Question 25

Levothyroxine T4 Used for

Answer 25

Hypothyroidism Suppression TSH in cases of benign nodules or large mutinodular goiter Hashimoto's Suppression of TSH thyroid carcinoma

Question 26

Levothyroxine T4 IV for...

Answer 26

Treating myxedema coma Life threatening situation Severe hypothyroidism

Question 27

Levothyroxine T4 Drug interactions

Answer 27

Ca carbonate Aluminum hydroxide Cholestyramine Colesevelam

Question 28

Levothyroxine T4 Agents that alter TBG

Answer 28

Estrogen inc TBG Clinical action: inc T4 Glucocorticoids, anabolic steroids dec TBG

Question 29

Levothyroxine T4 Agents that inhibit 5 deiodinase

Answer 29

Propylthiouracil Amiodarone

Question 30

Levothyroxine T4 ADR

Answer 30

Cardiovascular

Question 31

Hyperthyroidism MC cause

Answer 31

Graves' disease: abs bind to TSH receptors=>inc T4 production (elevated T4, T3, but low TSH)

Question 32

Hyperthyroidism Tx

Answer 32

Thionamides: propylthiouracil and methimazole

Question 33

Propylthiouracil and methimazole (antithyroids) MOA

Answer 33

Inhibit iodide incorporation into tyrosine residues Inhibit iodotyrosyl coupling to form iodothyronine Propylthiouracil inhibits peripheral 5-deiodinase (D1) conversion of T4 to T3

Question 34

Propylthiouracil and methimazole (antithyroids) Use

Answer 34

Hyperthyroidism Propylthiouracil preferred drug in pregnancy Methimazole: half life 6 hr (propylthiouracil: 1 hr)

Question 35

Propylthiouracil and methimazole (antithyroids) ADR

Answer 35

Methimazole: agranulocytosis and aplastic anemia Propylthiouracil: hepatic necrosis and nephritis

Question 36

Propylthiouracil and methimazole (antithyroids) Block box warning

Answer 36

Propylthiouracil ass with liver injury and failure