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endocrine (mine) > thyroid axis + physiology > Flashcards

thyroid axis + physiology Flashcards

1
Q

where is TRH released from

A

hypothalamus

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2
Q

what does TRH do, what does it stand for

A

thyrotropin releasing hormone

stimulates the anterior pituitary to produce TSH

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3
Q

where is TSH released from

A

anterior pituitary

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4
Q

what does TSH stand for, what does it do

A

thyroid stimulating hormone

stimulates the thyroid gland to produce T4 and T3

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5
Q

what does TRH act on

A

anterior pituitary

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6
Q

what does TSH act on

A

thyroid

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7
Q

what does high TSH suggest

A

hypothyroidism

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8
Q

what does low TSH suggest

A

hyperthyroidism

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9
Q

when are TSH levels unreliable

A

during acute illness or if there is pituitary disease present

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10
Q

where is T4 and T3 produced

A

colloid thyroglobulins which are located within the follicular cells of the thyroid

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11
Q

what is T4

A

thyroxine

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12
Q

what is T3

A

triiodothyronine

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13
Q

what percentage of all thyroid hormones does T4 and T3 make up

A 
T3 = 10%
T4 = 90%
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14
Q

which is the more active thyroid hormone, how much more active? why?

A

T3

x4 more active than T4 as it remains mostly free within the blood

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15
Q

what happens to T4 in body cells

A

it is converted to T3

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16
Q

what is T4 made up of

A

DIT + DIT

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17
Q

what is T3 made up of

A

DIT + MIT

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18
Q

how does low temperature affect thyroid hormones, in who does this happen

A

low temp = high TRH

in children and babies

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19
Q

how does stress affect thyroid hormones

A

stress = decreased TSH & TRH

20
Q

how does the circadian rhythm affect thyroid hormones

A 
night = high levels of hormone
morning = low levels of hormone
21
Q

what does deiodinase enzymes do

A

adds or removes an iodine atom from the thyroid hormones

22
Q

how many types of deiodinase enzymes are there

A

3

23
Q

where is type 1 deiodinase enzyme found

A

liver & kidney

24
Q

where is type 2 deiodinase enzymes found

A

everywhere! - heart, CNS, fat, brain pituitary

25
Q

what does type 2 deiodinase enzyme do

A

turns T4 to T3

26
Q

where is type 3 deiodinase enzyme found

A

placenta, foetal tissues, brain except from hypothalamus)

27
Q

what does type 3 deiodinase enzyme do

A

inactivated T3 and T4

28
Q

where is the thyroid gland normally located

A

C5/6-T1

along the thyroglossal duct

29
Q

what does the thyroid develop from, how does it descend

A

evagination of the pharyngeal epithelium that descends from the foramen caecum to the normal location

30
Q

what are the abnormalities thatch occur during the descent of the thyroid, what do they result in

A

failure to descend = lingual thyroid
excessive descent = retrosternal location in the mediastinum
thyroglossal duct cyst

31
Q

what is the thyroid composed of

A

follicles surround by flat/cuboidal follicular epithelial cells

32
Q

what makes up the thyroid follicles

A

dense, pink material that contains thyroglobulin

occasionally there are some C cells

33
Q

what are C cells, what do they secrete

A

C cells = parafollicular cells

they secrete calcitonin

34
Q

how are T3 and T4 synthesised

A

iodine is take up by the follicle cells where it attaches to tyrosine residues on thyroglobulin to form MIT and DIT. these then couple to form T3 and T4

35
Q

attachment if iodine to thyroglobulin residues are inhibited by what drugs

A

carbimazole

propylthiouracil

36
Q

how does T3 & T4 travel in the blood, why?

A

they are hydrophilic so must bind to plasma proteins to travel in the blood

37
Q

give examples of plasma binding proteins and their percentages

A

thyroxine binding globulin (TBG) = 70%
thyroxine binding prealbumin (TBPA) = 20%
albumin = 5%

38
Q

what hormone does thyroxine binding globulin (TBG) bind to more strongly

A

T4

39
Q

when do thyroxine binding globulin (TBG) levels naturally increase

A

pregnancy

on the contraceptive pill

40
Q

what is the effect of thyroid hormones on basal metabolic rate, how does this happen

A

INCREASES basal metabolic rate by:

increasing size + number of mitochondria
increasing O2 use and rate of ATP hydrolysis
increasing synthesis of respiratory chain enzymes

41
Q

what is the effect of thyroid hormones on thermogenesis

A

INCREASE

42
Q

what is the effect of thyroid hormones on carbohydrate metabolism

A

INCREASES:

stimulation of glycogenolysis and gluconeogenesis = increase blood glucose
insulin-dependent glucose uptake

43
Q

what is the effect of thyroid hormones on lipid metabolism

A

mobilise fats from adipose tissue

increases fatty axis oxidation in tissues

44
Q

what is the effect of thyroid hormones on protein metabolism

A

INCREASES protein synthesis

45
Q

what is the effect of thyroid hormones on  permissive symoathomimetic action

A

increase responsiveness to adrenaline and noradrenaline by increasing the number of receptors
cardiovascular responsiveness is increased

endocrine (mine) (12 decks)

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