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FHB - Endocrinology (by Richie) > L74: Thyroid & HPT Axis > Flashcards

L74: Thyroid & HPT Axis Flashcards

1
Q

Anterior to cricoid cartilage

A

Location of thyroid gland

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2
Q

Two symmetrical lobes fused by

A

isthmus

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3
Q

blood supply by

A

sup and inf thyroid artery….forms a plexus

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4
Q

C-cells produce

A

calcitonin

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5
Q

2 precursors of thyroid hormone

A
  1. Iodide 2. Thyroglobulin
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6
Q

Very high doses of Iodide will

A

rapidly shut down thyroid hormone production in hyperhroid patients

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7
Q

Thyroid perixidase TPO

A

oxidizes iodide to iodine…

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8
Q

What inhibits TPO?

A

Carbimazole (among other drugs)….so you can’t oxidize I2 into I-…ultimately cant make thyroid hormone

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9
Q

DIT + DIT =

A

T4

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10
Q

MIT + DIT =

A

T3

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11
Q

Megalin

A

Endocytoses the TG-T3/4 complex from the colloid into the follicular cell.

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12
Q

Each step is under TSH control

A

?

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13
Q

What’s NIS?

A

Sodium iodide symporter

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14
Q

Diagnostic thyroid gland tests

A

?

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15
Q

>60% uptake

A

?

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16
Q

Graves disease

A

Antibodies stimulate TSH receptor

Elevated T4/T3

Goiter (symmetrical)

Tachycardia, opthalmopathy, irritability, hyperactivity, heat intolerance, weight loss, nervousness, muscle wasting.

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17
Q

Organification defect

A

I- cannot be added to thyroglobulin in colloid.

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18
Q

Predominant in liver

A

Type I de-iodinase

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19
Q

Type II

A

?

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20
Q

Type III

A

?

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21
Q

Type IIi

A

Inner ring deiodinase (makes reverse T3)

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22
Q

Type II

A

mainly in brain and pituitary (this is the T3 being sensed by pit thyrotropes that is the negative feedback signal)….also in placenta

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23
Q

Which has highest affinity for T4?

A

TBG

24
Q

Upon TSH stimulation, follicular cells (surrounding colloid) turn from

A

squamous to cuboidal

25
Q

Inactivated follicles have flattened _____ epithelium

A

squamous

26
Q

Parafollicular cells (C-cells) secrete

A

Calcitonin

27
Q

5 cell types thyroid gland

A

Epithelial Fibroblasts Lymphocytes Adipocytes C-cells

28
Q

Parafollicular cells dont touch

A

colloid

29
Q

2 precursors for TH

A

Iodide

Thyroglobulin

30
Q

Less than 20micrograms per day of Iodine

A

Iodine deficiency

31
Q

“Increases in iodide intake decrease gland transport and hormone synthesis, and visa versa”

A

Wolf-Chaikoff Effect.

Note: this explains why excess Iodine will shut down hyperthyroidism….

32
Q

What hypothalamic nucleus makes TRH?

A

PVN

33
Q

What hypothalamic nucleus makes TSH?

A

Trick question! TRH is from hypothalamus

34
Q

What blocks NIS?

A

Perchlorate

Lithium

35
Q

Half life of T4

A

7-8 days because binds TBG

Binds receptor with LOW affinity

36
Q

T4 to T3 via what enzyme?

A

De-iodinases (I, II, III)

37
Q

Type 1 De-iodinase removes Iodide from

A

outer or inner ring

38
Q

Type 2 De-iodinase

A

outer ring deiodinase

39
Q

What deiodinase will make T4 into active T3?

A

Type II deiodinase because it removes outer ring iodine.

Found in brain, pituitary, placenta, and cardiac tissue.

40
Q

Only deodinase in thyroid gland itself

A

Type I de-iodinase

41
Q

Only way to get T3 into the blood via what de-iodinase?

A

Type I deiodinase (located in thyroid! think about it.)

42
Q

Type ____ deodinase is the thyroid hormone “sensor” in the pituitary, thus INHIBITING IT.

A

Type II de-iodinase

43
Q

Which deiodinase is protective so you dont make too much active T3?

A

Type 3 de-iodinase

44
Q

EVEN THOUGH its a peptide hormone, TH needs to be

A

bound to TBG in the blood (99%)

45
Q

How does it make sense that 70% of TH is bound to TBG, even though theres less TBG than albumin?

A

TBG has a higher affinity for TH than albumin!

46
Q

What does estrogen and hepatitis do to TBG?

A

Increase TBG, thus increasing binding of T3/4 in circulation

47
Q

Is TH receptor intracellular or extracellular?

A

Intracellular! Acts like a steroid hormone by affecting transcription

48
Q

Cretinism

A

Iodine deficiency

Small body, mental retardation..

49
Q

T3 effect on heart

A

Increased SV

Increased HR

Increased CO

50
Q

Ab against TPO

A

Hashimotos. Autoimmune; can’t make I- from I2

GOITER

51
Q

GOITER can be the result of

A

Hashimotos

Graves

Iodine deficiency

52
Q

Thyroid storm

A

Hyperthyroid person with a severe illness. Inflammatory response and excessive T4/3 potentiates the cytokine response. Fever, tachycardia, altered mental status.

Note: excessive palpation of thyroid

53
Q

Which DECREASES serum cholesterol levels: hypothyroid or hyperthyroid?

A

Hyperthyroid

54
Q

What does hyperthyroidism do to Beta adrenergic receptors?

A

upregulates them. thats why you get arryhthmia

55
Q

net cardiac effect of T3?

A

increased CO and HR

56
Q
A

FHB - Endocrinology (by Richie) (24 decks)

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