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Endocrine > Thyroid Hormones > Flashcards

Thyroid Hormones Flashcards

1
Q

Thyroid gland anatomy

A

follicles: thyroglobulin solution-filled lumen surrounded by thyroid cells; parathyroid cells b/w follicles synthesize calcitonin

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2
Q

What element is needed for thyroid hormone synthesis

A

IODIDE

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3
Q

Iodide transport

A

Stimulated by TSH= Actively transported into thyroid cells through NA/I symporter; I- is transported from the cell to the follicular lumen via pendrin

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4
Q

Na/I symporter

A

transports Na and I into thyroid cells (TSH stimulated)

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5
Q

Pendrin

A

causes I to move from the thyroid cell into the follicular lumen

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6
Q

Thiocyanate and perchlorate

A

BLOCK NIS transport of iodide

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7
Q

How would renal disease affect the thyroid gland?

A

affect the reabsorption of iodide

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8
Q

Production of T3 and T4

A

thyroglobulin produced by thyroid cells is excreted into lumen and iodine in lumen it reacts with the tyrosine’s (generating MIT) then sequentially DIT; coupling of MIT/DIT generates T3 and T4

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9
Q

MIT and DIT

A

are precursors to T3 and T4 and are biologically inactive

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10
Q

Thyroid peroxidase

A

Uses H2O2 to oxidize I-; also couples MIT and DIT molecules

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11
Q

Organification of the Iodide

A

menas the iodide is added to the tyrosine of the thyroglobulin molecule

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12
Q

T4 is formed by

A

2 DIT molecules

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13
Q

T3 is formed by

A

1 MIT and 1 DIT molecules

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14
Q

Propylthiouracil

A

inhibits the thyroperoxidases (TP); treatment for hyperthyroidism

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15
Q

Wolff-Chaikoff Effect

A

Excessive extracellular iodide is counteracted by an inhibition of organification (H2O2) of the iodide in the thyroid follicles, therefore inhibiting T3 and T4 production

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16
Q

Storage of Thyroid hormones

A

Large amounts stored in follicle attached to thyroglobulin

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17
Q

Body cannot store iodide so it stores

A

thyroid hormones in excess to circumvent a iodide shortage

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18
Q

Secretion of thyroid hormone

A

TSH-dependent megalin receptor causes endocytosis of thyroglobulin by thyroid cells; lysosomes fuse and cleave T3 and T4

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19
Q

Megalin

A

receptor that mobilizes the thyroglobulin colloid droplet from the lumen

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20
Q

Cathepsin

A

lysosomal enzyme that cleaves T3 and T4 from thyroglobulin

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21
Q

T4 is solely made by the

A

thyroid gland

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22
Q

T3 is made by

A

the thyroid gland and the liver cleaves T4 to T3

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23
Q

5’-deiodinase (D1, D2, D3 depending on location)

A

D1 in the liver; removes iodine from T4 to make T3

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24
Q

D1 deiodinase (removes iodide from outer ring)

A

liver and kidney and thyroid

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25
Q

D2 deiodinase (removes iodide from outer ring)

A

CNA and placenta

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26
Q

D3 deiodinase (removes iodide from inner ring)

A

peripheral tissue; reverses T3 producing inactive rT3

27
Q

Deiodinases TYPE I that activate T3 are inhibited by

A

fasting, severe illness, high glucocorticoids, drugs, fetuses

28
Q

Why doesn’t TSH stimulate more thyroid hormone production when fasting is inhibiting T3 production?

A

Because fasting only inhibits type I, type II deiodinase in the CNS is still active and therefore the pituitary still recognizes a higher level of T3 hormone

29
Q

T3 and T4 are bound (except 1%) to transport proteins

A

only free hormone is active

30
Q

Thyroid hormone transport proteins:

A

Thyroxine-binding globulin (TBG), albumin, thyroxine-binding pre-albumin

31
Q

Production of TBG alters

A

the amount of free vs bound T3 and T4

32
Q

Thyroid hormones effects

A

T3 (T4 little direct effect) increases O2 consumption, ATP synthesis, causes PM to become for permeable to solutes, enhances mito conversion of substrates to energy, and induces protein synthesis of mito enzymes

33
Q

Thyroid hormone results in

A

thermogenesis and heat production, increased metabolism, and O2 consumption

34
Q

Which tissues do not have effects of T3 and T4

A

brain, spleen, anterior pituitary, and gonads

35
Q

A major contributor to the heat production is

A

Na/K ATPase which generates ADP, stimulates O2 consumption and heat production

36
Q

Thermogenin

A

protein induced by T3 that uncouples OX PHOS and ATP generation to produce heat without generating ATP

37
Q

Metabolic effects of thyroid hormones

A

increases Carb, Fat and protein metabolism

38
Q

Thyroid hormones are permissive to

A

EPI, GH, and Insulin

39
Q

Thyroid hormone effect son the heart

A

to increase HR, SV, and CO by increasing the adrenergic activity and increasing transcription of beta receptors, Ca-ATPases, G proteins, A.C.

40
Q

Why would a beta blocker work to treat hyperthyroidism

A

to decrease HR, SV, and CO and MAP caused by increased T3

41
Q

Thyroid hormone effect on respiration

A

increased rate of ventilation, increased RBC production

42
Q

Thyroid hormone effect on brain

A

NO EFFECT on metabolism; but important for brian development

43
Q

Thyroid hormone effect on growth

A

permissive to GH, necessary for normal growth and development in children

44
Q

Metabolism of thyroid hormones

A

de-iodination and excretion through feces

45
Q

TRH stimulates and SS inhibits

A

TSH release from the anterior pituitary; TSH enhances Iodine trapping, T3/T4 liberation, and thyroid tissue growth

46
Q

T3 and T3 negative feedback

A

inhibits anterior pituitary and hypothalamus (reducing TRH and TRH receptor #) increases SS to inhibit TSH secretion

47
Q

Why would you see a goiter in hyperthyroidism?

A

TSH is overstimulated, TSH is trophic meaning it causes growth of the thyroid gland

48
Q

What would the labs look like for hypersecretion of T3 and T4

A

increased T3 and T4

49
Q

What would the labs look like for hypersecretion of TSH or secondary hypersecretion of T3 and T4

A

increased TSH and T3 and T4

50
Q

What would the labs look like for hypersecretion of TRH

A

increased TRH, TSH, and T3 and T4

51
Q

What would the labs look like for inability of thyroid

A

increased TRH and TSH, decreased T3 and T4

52
Q

Estrogens increase TBG, effect?

A

increased total serum concentration of T3 and T4 and also increases TRH sensitivity

53
Q

Age effect thyroid function?

A

T4 serum levels remain constant, BUT T3 declines with age

54
Q

GLUCOCORTICOIDS effect thyroid?

A

DEPRESS pituitary secretion of TSH (cortisol and dexamethasone)

55
Q

Severe illness effects thyroid hormones

A

increases rT3 and peripheral metabolism of T4, generating inactive thyroid hormones to slow “sick hypothyroidism”

56
Q

Acute iodine deficiency

A

T4 plasma levels decrease, TSH increases, and T3 is being generated in the thyroid at higher rates (T3 requires less I and is more potent)

57
Q

Chronic iodine deficiency

A

T3 and T4 levels fall and TSH is chronically active causing hypertrophy of the thyroid gland (goiter)

58
Q

Tumor in AP that secretes TSH

A

cause increased levels of T3 and T4 and TSH

59
Q

Atrophy of AP

A

increased TRH, decreased TSH, T3, and T4

60
Q

Abnormal stimulation of the thyroid gland

A

increased T3 and T4, decreased TSH

61
Q

destruction of thyroud gland

A

decreased T3 and T4 despite high levels of TSH

62
Q

Systemic illness

A

decreased T3, and NORMAL TSH and T4

63
Q

acute iodine deficiency

A

Increased TSH, normal T3, low T4

Endocrine (9 decks)

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