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Physiology II > Endocrine: Thyroid > Flashcards

Endocrine: Thyroid Flashcards

1
Q

Parafollicular cells release…

A

calcitonin

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2
Q

what is the functional unit of the thyroid?

A

follicular cell

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3
Q

hyperthyroid results in ______ reabsorption, and

A

colloid reabsorption, narrowed lumen

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4
Q

hypothyroid results in _____ cells

A

widened lumen

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5
Q

4 major steps of thyroid hormone synthesis?

A

iodide uptake, incorporation of iodide to tyr, coupling, diffusion

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6
Q

TSH binding on the basolateral membrane of follicular cells has what effect?

A

stimulates all steps of thyroid hormone synth

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7
Q

What inhibits TSH and TRH release?

A

T3/T4 increase

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8
Q

What 4 biologic effects occur when TSH binds to basolateral receptor?

A

increased NIS, Tg, TPO, T3/T4

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9
Q

What is responsible for peripheral conversion of T4 to T3?

A

peripheral deiodinases

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10
Q

What is the daily intake of iodide?

A

400 ug

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11
Q

total iodide content of the thyroid is…

A

7500 ug

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12
Q

What is the ratio of iodide in hormone to the amount of daily turnover? What effect does this have?

A

100:1, protects from deficiency for 2 months

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13
Q

What percent of iodide is released as HI/Free?

A

1% (70-80 ug)

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14
Q

What provides energy for the 2:1 na:iodide co-transport of the NIS?

A

Sodium gradient from sodium potassium pump

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15
Q

Once in the cell, _____ allows some iodide efflux to colloid

A

anoctamin-1 (anion channel)

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16
Q

low iodide has what effect on NIS activity?

A

increased

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17
Q

What effects does diet-induced iodide deficiency have on TSH release?

A

lack of T3/T4 production, no negative feedback, increased TSH secretion, increased NIS activity

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18
Q

Mutated NIS in ITD has what effect?

A

reduced T3/T4

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19
Q

what provides iodide for thyroid hormone synthesis in infants?

A

NIS in mammary gland

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20
Q

Is NIS activity in lactating glands under TSH regulation?

A

no

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21
Q

In Graves disease, anti-bodies are directed against…

A

TSH receptor, NIS

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22
Q

In grave’s disease, what causes growth of the thyroid?

A

thyroid stimulating immunoglobulins

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23
Q

Graves disease results in hyper/hypothyroidism, having what effect on TSH?

A

Hyperthyroidism, decreased TSH

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24
Q

What substances inhibits NIS?

A

perchlorate and thiocyanate

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25
Q

___ reflects activity of the thyroid gland, and can be measured via iodine 123 tracer…

A

NIS

26
Q

when iodine cannot be incorporated into tyrosine, it is called….

A

organification defect

27
Q

What carries iodide inside the follicular cell across the apical membrane

A

pendrine

28
Q

This disease:

  • goiter in childhood
  • hearing loss
  • hypothyroidism
  • gene mutation
A

pendred syndrome

29
Q

What oxidizes iodide to iodine for Tyr binding?

A

TPO using H2O2

30
Q

Iodide is bound to tyr residues on ____ by which enzyme? (organification)

A

binds tyr on Thyroglobulin via TPO

31
Q

Coupling occurs when iodinated tyrosines on Tg take on tertiary and quaternary form. Couling yields what two products?

A

monoiodinated tyrosine (MIT)

diiodinated tyrosine (DIT)

32
Q

20% of tyr residues on Tg will be iodinated. What percent will be coupled to become active thyroid hormones?

A

5%

33
Q

Iodide organification can occur independent of TSH in high plasma iodide conentrations.

Iodide itself can inhibit organification in order to prevent excess thyroid hormone production. What is this called?

A

wolff-chaikoff effect

34
Q

how long does wolf-chaikoff inhibition last?

A

few days, reduced iodine

35
Q

Two DIT =

A

T4

36
Q

MIT + DIT =

A

T3

37
Q

Where does the Tg molecule with T3/T4 get stored in the cell? Until when?

A

stored in colloid until TSH stimulation

38
Q

Follicular cell engulfs the T3/T4 containing Tg via…

A

megalin

39
Q

in the follicular cell, what frees T3 and T4 from MIT and DIT?

A

intrathyroidal deiodinase

40
Q

Hyperthyroidism is associated with an increase in what serum value?

A

high Tg levels in plasma due to leakage

41
Q

What inhibits coupling and oxidation of iodide?

A

propylthiouricil (Graves Tx)

42
Q

What 4 proteins do thyroid hormones bind to in the blood?

A

TBG, albumin, transthyretin, lipoprotein

43
Q

What percent of each thyroid hormone is secreted from thyroid?

A

90% T4

10 % T3

44
Q

what percent of T3 and T4 are bound in the blood?

A

99+%

45
Q

What type of deiodinases activate T4 to T3 via outer ring deiodination?

A

Type 1 & Type 2 deiodinases

46
Q

Which deiodinase inactivates T4 via inner ring deiodination?

A

Deiodinase Type 3

47
Q

What 4 types of transporters bring thyroid hormones into the cell?

A

NTCP

OATP

LAT

MCT

48
Q

Which transporter has preference for T4?

A

OATP

49
Q

Which transporter has preference for T3?

A

MCT

50
Q

Mutations in which receptor are assoc. with physchomotor retardation and thyroid hormone resistance?

A

MCT

51
Q

Are thyroid hormone carriers present at the BBB?

A

yes

52
Q

Thyroid hormones bind to nuclear DNA where?

A

TRE promoter region

53
Q

non-genomic effects of thyroid hormones increase stimulation of what channels?

A

(Calcium, sodium, potassium channels)

Ca ATPase, L-type calcium

sodium potassium pump, sodium and potassium channels

NHE

54
Q

What two calorigenic actions occur after T3/T4 stimulation?

A

increased BMR, body temp via sodium potassium pump

55
Q

Where do calorigenic actions not occur?

A

brain, gonads, spleen

56
Q

In the SNS, thyroid hormones increase synthesis of ______ via heterologues up-regulation

A

b-adrenergic (heart, skeletal, adipose)

57
Q

What effect does thyroid hormone stimulation have on the heart?

A

increased CO, chronotropic, inotropic, decreased resistance (vasodilation, temp. reg effect)

58
Q

What effects do thyroid hormones have on metabolism?

A

increased glucose absorption, gluconeogenesis, lipolysis, protein synth

increased proteolysis

59
Q

Tx for Graves…

A

surgery, radiation, beta blockers, PTU

60
Q

Hypo or hyper thyroid?

weight gain
cold intolerance
sleepiness
depression
slow pulse
HTN
A

hypo

61
Q

Hypo or hyper thyroid?

increased appetite
weight loss
heat intolerance
nervousness
anxiety
tremor
Increased SBP
Muscle weakness
A

hyper

Physiology II (28 decks)

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