Thyroid Phys- Trachte Flashcards Preview

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Flashcards in Thyroid Phys- Trachte Deck (39)
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1
Q

Describe the hypothalamic pituitary thyroid axis

A

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

2
Q

What other regulators DECREASE TRH/TSH release?

A

Somatostatin
Dopamine
High glucocorticoids

3
Q

What cells secrete TSH?

A

Thyrotropes

4
Q

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

A

Protein hormone

Receptor is in the plasma membrane

5
Q

What type of receptor does TRH bind?

A

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

6
Q

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

A

Gs coupled receptor

7
Q

What are the 3 thyroid hormone carrier proteins?

A

Thyroxine binding globulin (TBG)
Transthyretin
Albumin

8
Q

Which is more active T3 or T4?

A

T3!

9
Q

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

A

rT3 (basically removing the wrong iodine)

10
Q

How is iodine transported into the follicular cells?

A

Linked with Na

11
Q

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

A

INTRACELLULARLY!

Thyroid hormone MUST cross plasma membrane

12
Q

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

A

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

Binds a thyroid response element on DNA

Initiates gene transcription

13
Q

What are the 4 B’s of T3?

A

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

14
Q

What is cretinism?

A
Congenital lack of thyroid hormone in infants:
profound mental retardation
Short stature
Delay in motor development
Coarse hair
Protuberant abdomens
15
Q

How do most people get enough iodine in their diet?

A

Iodized salt!

16
Q

What is hashimoto’s?

A

autoimmune disease
anti-TSH antibodies??

Causes hypothyroidism

17
Q

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

A

Early diagnosis of hypothyroidism can prevent permanent mental retardation

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

18
Q

Cold intolerance is associated with…..

A

HYPOthyroidism

19
Q

Heat intolerance is associated with….

A

HYPERthyroidism

20
Q

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

A

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

High TSH
High TRH

21
Q

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

A

Pituitary deficiency would mean low TSH produced

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

22
Q

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

A

TH high
TSH high
TRH high

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

23
Q

What is grave’s disease?

A

Production of thyroid stimulating immunoglobulins (TSI)

The antibodies MIMIC TSH

24
Q

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

A

Antibodies mimic TSH - so there would be high TH

Low TRH
Low TSH (because of negative feedback)
25
Q

What is a goiter? when do you see it?

A

Goiter = enlarged thyroid gland

Can be seen in hypo or hyper thyroidism

26
Q

What would elevated TSH indicate?

A

Hypothyroidism

27
Q

What would low TSH levels indicate?

A

Hyperthyroidism

28
Q

How do you interpret the radioactive iodine uptake test?

A

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

29
Q

Levathyroxine

A

T4

30
Q

Liothyronine

A

T3

31
Q

How do thioamides work?

A

preventing iodide organization and thyroid peroxidase reactions to iodinate tyrosines

Treats hyperthyroidism

(methimazole, propylthiouracil, potassium iodide)

32
Q

Propylthiouracil

A

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

33
Q

Methimazole

A

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

Inhibition of thyroid hormone synthesis

34
Q

When would you use I(131)?

A

Radioactive iodine used from thyroid ablation

35
Q

When would you use I(123)?

A

Radioactive iodine used for thyroid imaging

36
Q

Which drug do you use for hyperthyroidism in pregnancy?

A

Propylthiouracil

37
Q

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

A

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

38
Q

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

A

Levothyroxine (T4) has a longer half life!!

39
Q

What would you use to treat graves disease?

A

Thioamides: Propylthiouraci and methimazole