Hellekant Thyroid

Question 1

What hormones decrease the release of TSH?

Answer 1

Somatostatin, dopamine, and high glucocorticoids

Question 2

Where are receptors for TRH found? What kind of receptors are they?

Answer 2

Anterior pituitary; transmembrane Gq receptors

Question 3

TSH is similar to what other hormones? Why?

Answer 3

Alpha chain of TSH is same as LH, FSH, placental hormone hCG

Question 4

What chain is specific to TSH and confers specificity of hormonal action?

Answer 4

Beta chain

Question 5

What cells have TSH receptor?

Answer 5

Thyroid follicular cells

Question 6

What type of receptor is the TSH receptor?

Answer 6

Plasmamembrane receptor; GCPR

Question 7

What dietary requirement is needed to synthesize thyroid hormones?

Answer 7

Iodide

Question 8

How is iodide brought into the thyroid follicular cell?

Answer 8

Via active transport with Na+

Question 9

After iodide is brought into the thyroid follicular cell, what happens next?

Answer 9

Iodide is transported to follicular lumen and undergoes oxidation to become iodine

Question 10

What enzyme is responsible for oxidation of iodide in thyroid hormone synthesis?

Answer 10

Thyroid peroxidase

Question 11

After oxidation to iodine, what is the next step in thyroid hormone synthesis? What enzyme is responsible for this?

Answer 11

Organification of iodine via thyroid peroxidase

Question 12

After organification, what is the next step in thyroid hormone synthesis? What enzyme is responsible for this?

Answer 12

Coupling via thyroid peroxidase

Question 13

What does thyroid peroxidase do?

Answer 13

Oxidation, organification, and coupling reactions

Question 14

What enzyme is responsible for converting T4 to T3?

Answer 14

5-deiodinase

Question 15

What thyroid hormone is more active? Has a shorter half life?

Answer 15

T3 is more active and has a shorter half life

Question 16

What proteins bind thyroid hormones?

Answer 16

Thyroid binding globulin (t3=t4), transthyretin (T4>T3), albumin (T3>T4)

Question 17

What increases the amount of thyroxine binding globulin?

Answer 17

Pregnancy or OCP use (estrogen)

Question 18

What decreases thyroxine binding globulin?

Answer 18

Hepatic failure, steroid use

Question 19

What is the function of deiodinase?

Answer 19

Converts T4 to T3

Question 20

Where is deiodinase I found?

Answer 20

Prevalent in liver and kidney

Question 21

What is the MOA of propylthiouracil?

Answer 21

Inhibits both thyroid peroxidase and 5-deiodinase

Question 22

Where is deiodinase II found?

Answer 22

Brian, pituitary, skeletal and cardiac muscle

Question 23

Where is deiodinase III found?

Answer 23

Brain, skin, placenta

Question 24

What is the function of deiodinase III?

Answer 24

Deactivates hormones

Question 25

What does TSH stimulate in the thyroid gland?

Answer 25

Secretion of mature thyroid hormones, increases thyroid peroxidase synthesis, thyroglobulin transcription, and Na/I transport activity

Question 26

What are the main functions of thyroid hormones?

Answer 26

Regulation of BMR, increased heat production, increased glucose utilizatin, uptake, and synthesis; increases HR and contractility

Question 27

What is Cretinism?

Answer 27

Congenital lack of thyroid hormone

Question 28

What are the symptoms of cretinism?

Answer 28

Profound mental retardation, short stature, delay in motor development, coarse hair, protuberant abdomens

Question 29

What are the signs of cretinism in newborns?

Answer 29

Resp difficulty, cyanosis, jaundice, horse cry, umbilical hernia, marked retardation of bone maturation

Question 30

What is the importance of assessing thyroid function at birth?

Answer 30

Early diagnosis can prevent permanent mental retardation; development can proceed normally

Question 31

What effect does thyroid hormones have on the sympathetic system?

Answer 31

Increases beta-1 receptors, resulting in increased HR and contractility

Question 32

What are the 4Bs of T3?

Answer 32

Brain maturation, bone growth, beta adrenergic effects, basal metabolic rate

Question 33

What effect does excess thyroid hormone have on bone?

Answer 33

Promote bone turnover, with net bone loss and hypercalciuria

Question 34

What effect does excess thyroid hormone have on cholesterol?

Answer 34

Increases in LDL receptor number, accelerating LDL clearance

Question 35

The thyroid-stimulating immunoglobulin test is used to diagnose what disease?

Answer 35

Graves

Question 36

What is a difference in release of TSH and T3/T4?

Answer 36

TSH has circadian rhythm, but T3/T4 do not

Question 37

Why does a goiter develop in iodine deficiency?

Answer 37

TSH stimulates Na/I transporter synthesis, thyroid peroxidase and thyroglobulin synthesis; this buildup can result in a mass

Question 38

Why does a goiter develop in Graves diseas?

Answer 38

Antibodies stimulate TSH receptor, resulting in lots of T3/T4 production

Question 39

What is levothyroxine?

Answer 39

T4

Question 40

What is liothyronine?

Answer 40

T3

Question 41

What drug can be used as T3 replacement?

Answer 41

Liothyronine

Question 42

What drug class is used for treatment of hyperthyroidism?

Answer 42

Thioamides

Question 43

What drugs are in the class thioamides?

Answer 43

Methimazole, carbimazole, propylthiouracil, potassium iodide

Question 44

What is used for thyroid ablation?

Answer 44

Iodine 131

Question 45

What radioactive iodine is used for thyroid imaging?

Answer 45

Iodide 123

Question 46

What decreases the absorption of levothyroxine?

Answer 46

Iron, calcium, AlOH, soy

Question 47

What drug is more potent, methimazole or PTU?

Answer 47

Methimazole is 10x more potent

Question 48

What is the MOA of propylthiouracil?

Answer 48

Inhibits thyroid peroxidase and inhibits deiodinase I

Question 49

What is the MOA of methimazole?

Answer 49

Inhibits thyroid peroxidase

Question 50

What are the uses for iodine in antithyroid therapy?

Answer 50

Thyroidectomy, to treat thyroid storm, and protection from radioactive iodine

Question 51

What is iodide 123 used for?

Answer 51

Thyroid scan

Question 52

What is Iodide 131 used for?

Answer 52

Destroy thyroid

Question 53

What is a major AE caused by propylthiouracil?

Answer 53

Hepatotoxicity

Question 54

What thioamide can cause ANCA associated antibodies?

Answer 54

PTU

Question 55

What thioamide is avoided in in 1st trimester?

Answer 55

Methimazole

Question 56

What is used to treat hyperthyroidism in 1st trimester of pregnancy?

Answer 56

PTU

Question 57

What teratogenic effects does methimazole have?

Answer 57

Aplasia cutis