Thyroid Phys- Trachte

Question 1

Describe the hypothalamic pituitary thyroid axis

Answer 1

TRH is secreted by hypothalamus

Initiates TSH secretion by anterior pituitary which goes to thymus

Initiates production of T3 and T4 thyroid hormones

T3 and T4 have systemic metabolic effects

Question 2

What other regulators DECREASE TRH/TSH release?

Answer 2

Somatostatin
Dopamine
High glucocorticoids

Question 3

What cells secrete TSH?

Answer 3

Thyrotropes

Question 4

What type of hormone is TRH? Where is its receptor on thyrotropes of the anterior pituitary?

Answer 4

Protein hormone

Receptor is in the plasma membrane

Question 5

What type of receptor does TRH bind?

Answer 5

G-protein linked (Gq) because it is couple to PLC and IP3

Question 6

What type of receptor does TSH bind on the thyroid follicular cells?

Answer 6

Gs coupled receptor

Question 7

What are the 3 thyroid hormone carrier proteins?

Answer 7

Thyroxine binding globulin (TBG)
Transthyretin
Albumin

Question 8

Which is more active T3 or T4?

Answer 8

T3!

Question 9

What would one convert T4 to in order to make it inactive for disposal?

Answer 9

rT3 (basically removing the wrong iodine)

Question 10

How is iodine transported into the follicular cells?

Answer 10

Linked with Na

Question 11

Where are the thyroid hormone receptors located on the target cell?

Answer 11

INTRACELLULARLY!

Thyroid hormone MUST cross plasma membrane

Question 12

Describe the steps following TH binding to it’s intracellular receptor…

Answer 12

The receptor either combines with and THR (homodimer) or retinoid X receptor (heterodimer)

Binds a thyroid response element on DNA

Initiates gene transcription

Question 13

What are the 4 B’s of T3?

Answer 13

Brain maturation
Bone Growth
B-adrenergic effects
Basal metabolic rate increase

Question 14

What is cretinism?

Answer 14

Congenital lack of thyroid hormone in infants:
profound mental retardation
Short stature
Delay in motor development
Coarse hair
Protuberant abdomens

Question 15

How do most people get enough iodine in their diet?

Answer 15

Iodized salt!

Question 16

What is hashimoto’s?

Answer 16

autoimmune disease
anti-TSH antibodies??

Causes hypothyroidism

Question 17

Why is there routine screening for TSH or T4 in the developed world?

Answer 17

Early diagnosis of hypothyroidism can prevent permanent mental retardation

If correction is delayed, physical development can be fixed, but mental delay cannot

Question 18

Cold intolerance is associated with…..

Answer 18

HYPOthyroidism

Question 19

Heat intolerance is associated with….

Answer 19

HYPERthyroidism

Question 20

What would happens to TRH, TSH, and TH in Hashimoto?

Answer 20

Hashimoto is antibodies to protein in thyroid gland - so low TH produced (no negative feedback)

High TSH
High TRH

Question 21

What happens to TRH, TSH, and TH is pituitary deficiency?

Answer 21

Pituitary deficiency would mean low TSH produced

Thus TH would be low
TRH would be high (no negative feedback)

Question 22

What happens to TRH, TSH, and TH if there is TH resistance (like a faulty TH receptor)

Answer 22

TH high
TSH high
TRH high

(it is the EFFECTS of TH binding to the receptor that actually induce the negative feedback)

Question 23

What is grave’s disease?

Answer 23

Production of thyroid stimulating immunoglobulins (TSI)

The antibodies MIMIC TSH

Question 24

What happens to TH, TSH, TRH in grave’s disease?

Answer 24

Antibodies mimic TSH - so there would be high TH

Low TRH
Low TSH (because of negative feedback)

Question 25

What is a goiter? when do you see it?

Answer 25

Goiter = enlarged thyroid gland

Can be seen in hypo or hyper thyroidism

Question 26

What would elevated TSH indicate?

Answer 26

Hypothyroidism

Question 27

What would low TSH levels indicate?

Answer 27

Hyperthyroidism

Question 28

How do you interpret the radioactive iodine uptake test?

Answer 28

Measures the amount of iodine the thyroid collects from the blood stream.

Low levels of iodine uptake might be a sign of hypothyroidism

High levels would support Grave’s diagnosis

Question 29

Levathyroxine

Answer 29

T4

Question 30

Liothyronine

Answer 30

T3

Question 31

How do thioamides work?

Answer 31

preventing iodide organization and thyroid peroxidase reactions to iodinate tyrosines

Treats hyperthyroidism

(methimazole, propylthiouracil, potassium iodide)

Question 32

Propylthiouracil

Answer 32

Blocks thyroide peroxidase, inhibiting oxidation of iodine and the conjugation reactions to make T3 & T4

Inhibition of thyroid hormone synthesis

Also blocks 5’-deiodinase so it decreases peripheral conversion of T4 to T3

Question 33

Methimazole

Answer 33

Blocks thyroide peroxidase, inhibiting oxidation of iodine and the conjugation reactions to make T3 & T4

Inhibition of thyroid hormone synthesis

Question 34

When would you use I(131)?

Answer 34

Radioactive iodine used from thyroid ablation

Question 35

When would you use I(123)?

Answer 35

Radioactive iodine used for thyroid imaging

Question 36

Which drug do you use for hyperthyroidism in pregnancy?

Answer 36

Propylthiouracil

Question 37

Why does pregnancy require an increased dose of Levothyroxine by 30-50%?

Answer 37

Pregnancy increases serum carrier proteins (and T4 is only active when it is FREE!)

Question 38

Why do we usually treat with levothyroxine over liothyronine for hypothyroidism?

Answer 38

Levothyroxine (T4) has a longer half life!!

Question 39

What would you use to treat graves disease?

Answer 39

Thioamides: Propylthiouraci and methimazole