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2 Endocrine > Physiology of the Thyroid Gland > Flashcards

Physiology of the Thyroid Gland Flashcards

1
Q

which endocrine grand secretes TRH?

A

hypothalamus

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2
Q

where does TRH go after it is secreted?

A

to the pituitary gland

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3
Q

what is TSH secreted by?

A

pituitary gland

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4
Q

what thyroid hormone does the thyroid primarily secrete?

A

T4

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5
Q

what does elevated T3/T4 in the blood plasma cause?

A

TSH to be inhibited

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6
Q

how is T3 made?

A

T4 is converted into it by deiodination

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7
Q

name all the thyroid hormones secreted by the thyroid gland?

A

T4
T3
calcitonin

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8
Q

what do the parathyroid glands produce?

A

parathyroid hormone

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9
Q

what vertebral levels is the thyroid gland located at?

A

C5-T1

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10
Q

what weight is the thyroid gland?

A

25-30g

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11
Q

when does the thyroid gland increase in size physiologically?

A

pregnancy

menstruation

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12
Q

parasympathetic innervation of the thyroid gland?

A

vagus nerve

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13
Q

sympathetic innervation of the thyroid gland?

A

superior, middle and inferior ganglia of the sympathetic trunk

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14
Q

arterial blood supply to the thyroid gland?

A

superior and inferior thyroid arteries

thyroid ima artery (embryological)

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15
Q

venous blood supply to the thyroid gland?

A

superior, middle and inferior thyroid vein

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16
Q

what vein(s) from the thyroid gland drain into the internal jugular vein?

A

superior and middle

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17
Q

what vein(s) from the thyroid gland drain into the brachiocephalic vein?

A

inferior

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18
Q

what is the berry ligament?

A

suspensory ligament located posteromedially to the thyroid gland

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19
Q

what should the thyroid look like on a technetium thyroid scan?

A

symmetrical darker areas over the lobes of the thyroid

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20
Q

what does the thyroid look like on a technetium thyroid scan of someone with graves disease?

A

darker, enlarged symmetrical lobes of the thyroid

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21
Q

what does the thyroid look like in hyperthyroidism?

A

1 lobe looks darker than the other

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22
Q

what cells in the thyroid make T3 and 4

A

follicular cells

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23
Q

where is colloid located?

A

in follicles of the thyroid

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24
Q

what is colloid?

A

tyrosine containing thyroglobulin filled with spheres enclosed by follicular cells

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25
Q

what cells secrete calcitonin?

A

parafollicular C cells

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26
Q

important role of calcitonin in cancer?

A

is a tumour marker for MEDULLARY thyroid cancer

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27
Q

how can free T3 and 4 produced by the colloid get back into the bloodstream?

A

colloid undergoes pinocytosis
some hormones go back into follicular cells
hormones are released into bloodstream

28
Q

what do follicular cells do?

A

make T3 and 4
control uptake of iodine into thyroid
regulates hormones moving in/out of bloodstream

29
Q

what does the colloid do?

A

contains a reservoir of thyroid hormone

30
Q

how is T3 made?

A

iodine taken up by follicular cells,
iodine attaches to tyrosine residues on thyroglobulin to make monoiodotyrosine and di-iodotyrosine units,
1 MIT + 1 DIT = T3

31
Q

how is T4 made?

A

iodine taken up by follicular cells,
iodine attaches to tyrosine residues on thyroglobulin to make monoiodotyrosine and di-iodotyrosine units,
1 MIT + 3DIT = T4

32
Q

how do carbimazole and propylthiouracil stop new T3/4 production?

A

stop iodine attaching to tyrosine residues i.e preventing deiodination

33
Q

what is the major biologically active thyroid hormone?

A

T3

34
Q

how many times more potent is T3 than T4?

A

4 times

35
Q

is most TH found free or bound?

A

bound to plasma proteins

36
Q

what happens to the thyroid hormones in the colloid when TSH is in the bloodstream?

A

they are released via pinocytosis

37
Q

what does T3 act on?

A

the nucleus of follicular cells via gene transcription

38
Q

is T3/4 in blood the same as free T3/4?

A

no, free T3/4 is in colloid

39
Q

is bound or unbound thyroid hormone the biologically active form?

A

unbound

40
Q

what are the 3 plasma proteins that t3/4 bind to?

A

tbg
ttr
albumin

41
Q

why do t3/4 bind to plasma proteins?

A

they are hydrophobic

42
Q

is unbound or bound hormone available to the tissues?

A

unbound

43
Q

if TBG were to increase, what effect would it have on free and bound T3/4?

A

wouldnt affect free

would increase bound

44
Q

what liver and bile duct diseases increases tbg?

A

biliary cirrhosis
hep A
chronic hepatitis

45
Q

what kidney disease decreases tbg?

A

nephrotic syndrome

46
Q

does pregnancy increase or decrease tbg?

A

increase

47
Q

how do thyroid hormones increase basal metabolic rate?

A

increase no and size of mitochondria
increase oxygen use
increase synthesis of resp chain enzymes

48
Q

what effect do thyroid hormones have on blood glucose?

A

stimulate glycogenolysis and gluconeogenesis

49
Q

what effect do thyroid hormones have on lipids?

A

increase fatty acid oxidation

50
Q

what thyroid disease presents with slow intellectual function?

A

hypothyroidism

51
Q

what thyroid disease presents with nervousness and hyperkinesis?

A

hyperthyroidism

52
Q

what should TSH and thyroid hormone levels look like in normal people?

A

should stay the same throughout life

53
Q

why are beta blockers good for treating hyperthyroidism?

A

slow down tachycardia and chronotropic rate

54
Q

what effect do thyroid hormones have on TSH and TRH once they are in the blood stream?

A

switch off their production

55
Q

what kind of receptor is the TSH receptor?

A

GPCR

56
Q

what cell is the TSH receptor located on?

A

follicular cell

57
Q

if a patient had decreased t3/4 and decreased tsh what would you suspect?

A

stress

secondary hypothyroidism

58
Q

what effect does stress have on thyroid hormones?

A

inhibits TRH and TSH release

59
Q

how many kinds of deiodinase enzyme are there?

A

3 (D1, 2 and 3)

60
Q

what do the deiodinase enzymes do?

A

activate/deactivate thyroid hormones

61
Q

which type of deiodinase enzyme is foiund in perpheral tissues?

A

D2

62
Q

what type of deiodinase enzyme is found in pregnancy?

A

D3

63
Q

where is D1 deiodinase enzyme found?

A

liver

kidney

64
Q

what does D2 do?

A

converts T4 to T3 in tissues

65
Q

if T3 is low, what could be going on?

A

not enough D2

66
Q

what is cretinism and who gets it?

A

short stature and limiting mental function in children with thyroid hormone deficiency

67
Q

main regulator of thyroid hormone?

A

TSH

2 Endocrine (35 decks)

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