L74: Thyroid & HPT Axis Flashcards Preview

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

Flashcards in L74: Thyroid & HPT Axis Deck (56)
1

Anterior to cricoid cartilage

Location of thyroid gland

2

Two symmetrical lobes fused by

isthmus

3

blood supply by

sup and inf thyroid artery....forms a plexus

4

C-cells produce

calcitonin

5

2 precursors of thyroid hormone

1. Iodide 2. Thyroglobulin

6

Very high doses of Iodide will

rapidly shut down thyroid hormone production in hyperhroid patients

7

Thyroid perixidase TPO

oxidizes iodide to iodine...

8

What inhibits TPO?

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

9

DIT + DIT =

T4

10

MIT + DIT =

T3

11

Megalin

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

12

Each step is under TSH control

?

13

What's NIS?

Sodium iodide symporter

14

Diagnostic thyroid gland tests

?

15

>60% uptake

?

16

Graves disease

Antibodies stimulate TSH receptor

Elevated T4/T3

Goiter (symmetrical)

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

17

Organification defect

I- cannot be added to thyroglobulin in colloid.

18

Predominant in liver

Type I de-iodinase

19

Type II

?

20

Type III

?

21

Type IIi

Inner ring deiodinase (makes reverse T3)

22

Type II

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

23

Which has highest affinity for T4?

TBG

24

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

squamous to cuboidal

25

Inactivated follicles have flattened _____ epithelium

squamous

26

Parafollicular cells (C-cells) secrete

Calcitonin

27

5 cell types thyroid gland

Epithelial Fibroblasts Lymphocytes Adipocytes C-cells

28

Parafollicular cells dont touch

colloid

29

2 precursors for TH

Iodide

Thyroglobulin

30

Less than 20micrograms per day of Iodine

Iodine deficiency

31

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

Wolf-Chaikoff Effect.

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

32

What hypothalamic nucleus makes TRH?

PVN

33

What hypothalamic nucleus makes TSH?

Trick question! TRH is from hypothalamus

34

What blocks NIS?

Perchlorate

Lithium

35

Half life of T4

7-8 days because binds TBG

Binds receptor with LOW affinity

36

T4 to T3 via what enzyme?

De-iodinases (I, II, III)

37

Type 1 De-iodinase removes Iodide from

outer or inner ring

38

Type 2 De-iodinase

outer ring deiodinase

39

What deiodinase will make T4 into active T3?

Type II deiodinase because it removes outer ring iodine.

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

40

Only deodinase in thyroid gland itself

Type I de-iodinase

41

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

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

42

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

Type II de-iodinase

43

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

Type 3 de-iodinase

44

EVEN THOUGH its a peptide hormone, TH needs to be

bound to TBG in the blood (99%)

45

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

TBG has a higher affinity for TH than albumin!

46

What does estrogen and hepatitis do to TBG?

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

47

Is TH receptor intracellular or extracellular?

Intracellular! Acts like a steroid hormone by affecting transcription

48

Cretinism

Iodine deficiency

Small body, mental retardation..

49

T3 effect on heart

Increased SV

Increased HR

Increased CO

50

Ab against TPO

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

GOITER

51

GOITER can be the result of

Hashimotos

Graves

Iodine deficiency

52

Thyroid storm

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

Which DECREASES serum cholesterol levels: hypothyroid or hyperthyroid?

Hyperthyroid

54

What does hyperthyroidism do to Beta adrenergic receptors?

upregulates them. thats why you get arryhthmia

55

net cardiac effect of T3?

increased CO and HR

56