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OSSF > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

What is the major product of the thyroid gland

A

thyroxine (T4)

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2
Q

The backbone of TH is _____ and is synthesized in the ____

A

thyroglobulin, rER

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3
Q

Thyroglobulin is stored in ___

A

follicular colloid

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4
Q

How does iodide enter thyroid follicular cells

A

thyroid follicular cells trap and concentrate iodide via Na/O- symporter in basal membrane

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5
Q

How does iodide get into the colloid?

A

iodide is shuttled across the apical membrane by Cl-/I- transporter

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6
Q

What is the key enzyme in the production of thyroid hormone

A

thyroperoxidase

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7
Q

What are the three main rolls of thyroperoxidase

A

oxidize iodide to iodine
iodinate tyrosine melecules
condensation of MIT and DIT

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8
Q

TSH stimulates what three actions in the thyroid

A

I- uptake
throglobulin synthesis
endocytosis of colloid

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9
Q

How does methimazole work?

A

it inhibits TPO

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10
Q

What are goitrogens

A

they are substances that disrupt production of thyroid hormones

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11
Q

True/False: T4 is a prehormone for T3

A

true

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12
Q

Where is most T3 producted

A

in tissues via deiodination of T4

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13
Q

What are the three main binding proteins of TH

A

TBG, ALB, plasma lipoproteins

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14
Q

Where is TGB produced

A

the liver

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15
Q

what is the main TH binding protein in large animals and primates

A

TBG

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16
Q

What is the main TH binding protein in small animals

A

ALB

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17
Q

What TH binding protein has the highest affinity for T4?

18
Q

True/False: TBG has a higher affinity for T3 than T4

A

false, it has a higher binding affinity for T4

19
Q

How does estrogen, cortisol, and NSAIDS affect T4 protein binding?

A

estrogen increases binding while cortisol and NSAIDS compete for binding sites

20
Q

Typically with drug therapy (glucocorticoids and NSAIDS) fT4 is _____

A

cleared more rapidly due to the competitive binding initially yielding higher fT4 levels

21
Q

What are the two main factors that contribute to lower circulating T3 levels?

A

difference in TBG binding affinity and the difference in thyroid output

22
Q

True/False: TSH goal is to maintain fT4 levels

23
Q

with drug therapy (glucocorticoids, NSAIDS) bloodwork will show ____ fT4 values and ____ Total T4 values as compared to normal

A

normal, lower

24
Q

How does iodide concentration regulate thyroid hormone synthesis

A

excess iodide exerts negative feedback thus suppressing hormone synthesis

25
Q

What are the different deiodinases and what are their functions? where?

A

D1: T4 to T3 in most tissues
D2: T4 to T3 in brain
D3: main source of rT3

26
Q

True/False: a selenium deficiency will result in a decrease in T3 levels, why

A

True, because all deiodinases contain selenium so T4 wouldn’t be able to be converted to T3

27
Q

What is the purpose of rT3

A

it helps lower metabolic rate

28
Q

What are three example of conditions where D3 activity may increase yielding increase in rT3

A

starvation, hibernation, illness

29
Q

What is the main basic function of TH?

A

it affects expression of ~1% of genes in target tissues

30
Q

What is the effect of TH on O2 consumption and metabolic rate

A

TH increases consumption of O2 and basal metabolic rate

31
Q

What three tissues O2 consumption is not affected by TH

A

spleen, brain, testes

32
Q

Why do hyperthyroid cats tend to display agitated/ hyperactive behavior?

A

because in adults, TH has an excitatory effect on the CNS

33
Q

TH is essential for what 3 things during fetal development

A

Brain development, synapse formation, myelination

34
Q

Fetal hypothyroidism can present with:

A

decreased mentation and reflexes
stillbirths

35
Q

Why can you see angular limb deformaties in hypothyroid foals

A

because TH synergizes with GH and IGF-1 which promotes ossification, fusion of bone plates, and bone maturation

36
Q

If TH stimulates carbohydrate metabolism why does it not result in hyperglycemia

A

because it also enhances insulin dependent entry into cells

37
Q

True/False: plasma concentrations of cholesterol and TG are inversely correlated with thyroid hormone levels

38
Q

TH ____ EPO

A

stimulates

39
Q

True/false: TH increases beta:alpha adrenergic receptor ration

40
Q

What type of cardiovascular changes might you see in response to TH

A

vasodilation, increased HR, increased tissue profusion

41
Q

What is the affect of TH on the hair cycle

A

it initiates and maintains the anagen phase of the hair cycle

42
Q

What signs might you expect in a hypothyroid dog (4)?

A

anemia, hair loss, weight gain, heat seeking

OSSF (37 decks)

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