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OSSF 2 > Exam 3- Physiology of the Thyroid Gland and Thyroid Hormones > Flashcards

Exam 3- Physiology of the Thyroid Gland and Thyroid Hormones Flashcards

1
Q

thyroid hormone synthesis starts with synthesis of _______________

A

thyroglobulin

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2
Q

tetraiodothyronin (thyroxine; T4) is produced from __________

A

tyrosine

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3
Q

what do thyroid follicular cells do to iodide?

A

trap and concentrate it via Na/I symporter in basal membrane

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4
Q

how does iodide get into the colloid?

A

chloride/iodide transporter in apical membrane

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5
Q

what does thyroperoxidase (TPO) do?

A

oxidizes I- (iodide) to iodine
iodinates tyrosine molecules
produces monoiodotyrosine (MIT) and diiodotyrosine (DIT), thyroid hormone precursors

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6
Q

after making MIT and DIT, what does thyroperoxidase do?

A

cleaves and couples MIT or DIT to acceptor DIT residues

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7
Q

thyroperoxidase actions result in a mixture of ___, ___, ___, and ___ attached to the thyroglobulin backbone

A

MIT
DIT
T3
T4

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8
Q

how do the final thyroid hormones get into the blood?

A

diffuse through basal membrane after being cleaved

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9
Q

what mediates synthesis and secretion of thyroid hormone?

A

thyroid stimulating hormone: receptors on basal membranes, G protein mediated increase in cAMP

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10
Q

what does thyroid stimulating hormone stimulate?

A

I- uptake
thyroglobulin synthesis
endocytosis of colloid

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11
Q

what is most of the hormone released from the thyroid gland?

A

thyroxine (T4)

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12
Q

from where is most of the T3 in serum derived?

A

deiodination of T4 in tissues

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13
Q

is T3 or T4 more metabolically active?

A

T3

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14
Q

why is thyroid hormone bound?

A

prolongs the circulating half life and controls the blood hormone levels

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15
Q

what proteins bind thyroid hormone?

A

thyroid hormone-binding globulin (TBG)
albumin
plasma lipoproteins

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16
Q

how does estrogen affect thyroid hormone-binding globulin (TBG)?

A

increases: increases total T4

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17
Q

how do cortisol and NSAIDS affect thyroid hormone levels?

A

compete for binding sites: lower total levels because cause it to be cleared more

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18
Q

what regulates thyroid hormone?

A

hypothalamus and central nervous system

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19
Q

how does heat affect TRH?

A

decreased by heat
increased by cold

20
Q

true/false: excess iodide exerts negative feedback on thyroid hormone synthesis

A

true

21
Q

do deiodinases differ by tissue?

A

yes

22
Q

what does thyroid hormone (T3) bind to in the nucleus?

A

heterodimer with retinoid X receptor

23
Q

what is thyroid hormone essential for in development?

A

brain
synapse formation
myelination

24
Q

what does thyroid hormone do with erythropoiesis?

A

stimulates it

25
Q

what cell organelles are necessary for making thyroglobulin?

A

rER makes backbone
Golgi glycosylates and packages

26
Q

what stimulates the synthesis of thyroglobulin?

A

thyroid stimulating hormone

27
Q

what percent of the body’s iodide is in the thyroid?

A

> 90%

28
Q

where is coupling done?

A

thyroglobulin backbone

29
Q

what are goitrogens?

A

substances that disrupt production of thyroid hormones

30
Q

what is used to treat hyperthyroid cats?

A

methimazole

31
Q

what percent of the body’s T3 is produced by the thyroid?

A

20%

32
Q

what is the sequence for control of thyroid hormone?

A

thyrotropin releasing hormone from hypothalamus
thyroid stimulating hormone from thyrotropes in anterior pituitary
increased T4 release from thyroid
negative feedback from T4 to both hypothalamus and anterior pituitary

33
Q

how does cortisol affect thyroid stimulating hormone?

A

inhibits its secretion

34
Q

does iodide exert negative feedback on thyroid hormone?

A

yes: iodination thyroglobulin, thyroid hormone synthesis, and sensitivity to TSH

35
Q

what is the thyroid nuclear receptor specific for?

A

T3

36
Q

where is deiodinase 1 (D1) specific to?

A

liver, kidneys, thyroid, pituitary

37
Q

what deiodinase is the main source of rT3?

A

D3

38
Q

what deiodinase is specific to the brain?

A

D2
astroglia

39
Q

what substance is essential to iodinases?

A

selenium

40
Q

when is deiodinase 3 (D3) more active?

A

sustained catabolism periods (starvation, illness, hibernation)
fetus

41
Q

what does thyroid receptor do in the absence of hormone?

A

binds to co-repressor proteins that silence gene expression

42
Q

what is the thyroid receptor?

A

heterodimer with retinoid X receptor

43
Q

what does thyroid hormone do to the daily energy use?

A

increases it
free fatty acids mobilized and used
Na/K ATPase stimulated
increased body heat

44
Q

what does thyroid hormone synergize with in a young animal?

A

growth hormone and IGF-1

45
Q

how does thyroid hormone stimulate carbohydrate metabolism?

A

facilitates gluconeogenesis: enhances effects cortisol, epinephrine, growth hormone, glucagon
facilitates glycogenolysis
enhances absorption carbohydrates in intestine
enhances insulin-dependent entry into cells

46
Q

what does thyroid hormone do with fat metabolsm?

A

increases lipolysis
increases cholesterol synthesis, excretion in bile, and lipoprotein catabolism
increases triglyceride turnover and chylomicron clearance

47
Q

what does thyroid hormone do with the beta:alpha-adrenergic receptor ratio?

A

increases beta-adrenergic receptors

OSSF 2 (19 decks)

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