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BMS 618 Endocrine and Reproductive Systems > Wk1: Test1: 3 Thyroid Hormones: Synthesis, Actions, Regulation - Pierre > Flashcards

Wk1: Test1: 3 Thyroid Hormones: Synthesis, Actions, Regulation - Pierre Flashcards

1
Q

the thyroid gland is composed of

A

follicles

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2
Q

follicles are lined with — and filled with —

A

follicular cells

colloid

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3
Q

the colloid is primarily composed of

A

thyroglobulin (Tg)

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4
Q

thyroglobulin is synthesized by

A

follicular cells

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5
Q

— is taken up by follicular cells and combined with Tg (Thyroglobulin) to form — and —

A

Iodide

Thyroxine T4

Triiodothyronine T3

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6
Q

Follicular cells are also called — and are —

A

thyroid epithelial cells

polarized

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7
Q

What does polarized mean

A

the basolateral membrane is connected to the blood stream and the apical side is exposed to the colloid

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8
Q

Bidirectional Synthesis

A

iodide is taken up from the basolateral side, combined with Tg in colloid, T3 and T4 released on basolateral side

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9
Q

Step 1: Iodide uptake by — on the basolateral membrane. It is powered by the — ion pump

A

Sodium/ Iodide Symporter (NIS)

Na/K ATPase (NKA) Ion Pump

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10
Q

Mutation of the NIS gene is a rare cause of

A

congenital hypothyroidism

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11
Q

low iodide levels — the amount of NIS and stimulate —

A

increase

uptake of iodide

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12
Q

Low iodide levels — NIS expression and uptake

A

decrease

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13
Q

Step 2: along the apical membrane I- is transported into the lumen by a

A

anion exchanger - Pendrin

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14
Q

Mutation in pendrin gene causes —

A

Pendred Syndrome

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15
Q

Pendred Syndrome is characterized by

A

defective organification of iodine, goiter, and sensorineural deafness

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16
Q

Step 3: the enzyme — located at the apical border of the follicle cells catalyzes the oxidation of iodide to iodine

A

thyroperoxidase (TPO)

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17
Q

Step 4: — is synthesized and released into the lumen via exocytosis

A

Thyroglobulin (Tg)

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18
Q

Step 5: Tg is extruded into the lumen. 20% of its tyrosine residue is —. The catalyst of this reaction is —

A

iodinated

TPO

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19
Q

Step 5: The initial product of tyrosine iodination are — and —

A

monoiodotyrosine (MIT)

diiodotyrosine (DIT)

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20
Q

2 DITs coupled

A

T4 - Tetraiodothyronine

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21
Q

1 DIT and 1 MIT coupled

A

T3 - Triiothryonine

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22
Q

when iodine is abundant – is formed

when iodine is scarce — is formed

A

T4

T3

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23
Q

there is enough thyroid hormones stored as iodinated thyroglobulin in the colloid to last the body —

A

2-3 months

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24
Q

Step 6: When thyroid hormone is needed, — is “pinched” from the follicle

A

thyroglobulin

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25
Q

Step 7: Intracellular proteases cleave off — and —, MIT and DIT from —

A

T3, T4, Tg

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26
Q

Step 8: — and — are secreted and MIT and DIT are —

A

T3, T4

Recycled

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27
Q

Iodine deficiency is assessed by measuring —

A

iodide excreted

> 10ug/dL

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28
Q

Iodine deficiency is most severe in

A

pregnant women and their babies

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29
Q

T3 or T4 has higher binding affinity for proteins

A

T4

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30
Q

T4 half life

T3 half life

A

T4: 6-7 Days

T3: 1-2 Days

31
Q

most circulating thyroid hormone is —

there is 50x more than the other

A

T4

32
Q

the amount of circulation T3/T4 is – times the amount secreted by the thyroid each day

A

3x

33
Q

99% of T3/T4 is bound to

A

plasma binding protiens

34
Q

What 3 proteins bind T3 and T4

A

TBG

Albumin

Transthyretin TTR

35
Q

TBG binding affinity

A

80% T4>T3

36
Q

Albumin binding affinity

A

up to 10% of T4 and 30% T3

37
Q

TTR binding affinity

A

10% of T4

Little T3

38
Q

T3 or T4 binds their receptor with more affinity

A

T3

39
Q

T3 or T4 the more active thyroid hormone

A

T3

40
Q

Many target tissues can regulate the conversion

of T4 to

A

either T3 or reverse T3

41
Q

rT3 is not

A

biologically active

42
Q

Most of the circulating T3 is derived from the
peripheral conversion of — into T3 and its release
again into the circulation

A

T4

43
Q

Abnormal rate of conversion of T4 to rT3 is observed in

A

Euthyroid sick syndrome (ESS)

44
Q

T4 conversion to T3 via

A

5’ monodeiodinase

Activation

45
Q

T4 conversion to reverse T3

A

5 monodeiodinase

Degredation

46
Q

Thyroid hormone synthesis and secretion are

maintained within narrow limits because of a

A

very sensitive

negative feedback

47
Q

A 50% decrease in plasma T4

causes a — times increase in plasma TSH.

A

50-100

48
Q

— provides constant and necessary stimulus

for TSH secretion

A

TRH

49
Q

In the absence of TRH, the

secretion of TSH (and T4) does what

A

decreases to very low

levels

50
Q

The target tissue for TSH is the

A

thyroid where it increases the secretion of T4/T3.

51
Q

Negative feedback of thyroid hormones is exerted

mainly at the level of the

A

anterior pituitary gland

52
Q

Primary hyperthyroidism

A

low TSH

53
Q

Primary Hypothyroidism

A

High TSH

54
Q

Circulating T3/T4 enter cells by — and

specific transporters such the —

A

passive diffusion

monocarboxylase 8
transporter (MCT8)

55
Q

Mutations in the MCT8 gene have been linked to what thyroid function abnormalities

A

low T4, high T3, high TSH

56
Q

After entering cells, T3 and T4 act primarily through nuclear
receptors: the

A

thyroid hormone receptors (TRs).

57
Q

TRs bind to specific DNA sequences:

A

thyroid response elements (TREs) in the promoter region of target genes.

58
Q

TRs bind as homodimers or heterodimers with – receptors

A

retinoic

acid X receptors (RXR)

59
Q

activated TR can — the transcription of the target gene, depending on the nature of the regulatory elements.

A

stimulate or repress

60
Q

Mutations in TR can lead to —, suspected when unbound thyroid hormone levels are increased without
suppression of TSH.

A

thyroid hormone resistance (THR)

61
Q

Widespread Physiological Effects of Thyroid Hormone

A

see chart - slides 16 and 17

62
Q

Hyperthyroidism

A

over activity of thyroid leading to excess T4

63
Q

Hyperthyroidism is more common in men or women

A

women 5:1

64
Q

— is most common cause of hyperthyroidism

A

Grave’s Disease

65
Q

Euthyroidism

A

thyroid gland is functioning normally

66
Q

In — , thyroid test results can be abnormal even though

the thyroid gland is functioning normally (abnormal T3/rT3 ratio)

A

euthyroid sick syndrome (ESS)

67
Q

ESS occurs in people who

A

have a severe illness other than thyroid disease.

68
Q

Hypothyroidism

A

Underproduction of thyroid hormones. One of the most common thyroid disorders.

69
Q

Hypothyroidism more common in men or women

A

women 5 - 8 x

70
Q

— is the most common cause of hypothyroidism worldwide

A

iodine deficiency

71
Q

— is the most common cause of hypothyroidism in iodine sufficient areas

A

Hashimoto’s thyroiditis

72
Q

Effects of thyroid hormone on energy at cellular level

A
73
Q

Effects of thyroid hormone on energy at body level

A

BMS 618 Endocrine and Reproductive Systems (2 decks)

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