L74: Thyroid & HPT Axis

Question 1

Anterior to cricoid cartilage

Answer 1

Location of thyroid gland

Question 2

Two symmetrical lobes fused by

Answer 2

isthmus

Question 3

blood supply by

Answer 3

sup and inf thyroid artery….forms a plexus

Question 4

C-cells produce

Answer 4

calcitonin

Question 5

2 precursors of thyroid hormone

Answer 5

1. Iodide 2. Thyroglobulin

Question 6

Very high doses of Iodide will

Answer 6

rapidly shut down thyroid hormone production in hyperhroid patients

Question 7

Thyroid perixidase TPO

Answer 7

oxidizes iodide to iodine…

Question 8

What inhibits TPO?

Answer 8

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

Question 9

DIT + DIT =

Answer 9

T4

Question 10

MIT + DIT =

Answer 10

T3

Question 11

Megalin

Answer 11

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

Question 12

Each step is under TSH control

Answer 12

?

Question 13

What’s NIS?

Answer 13

Sodium iodide symporter

Question 14

Diagnostic thyroid gland tests

Answer 14

?

Question 15

>60% uptake

Answer 15

?

Question 16

Graves disease

Answer 16

Antibodies stimulate TSH receptor

Elevated T4/T3

Goiter (symmetrical)

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

Question 17

Organification defect

Answer 17

I- cannot be added to thyroglobulin in colloid.

Question 18

Predominant in liver

Answer 18

Type I de-iodinase

Question 19

Type II

Answer 19

?

Question 20

Type III

Answer 20

?

Question 21

Type IIi

Answer 21

Inner ring deiodinase (makes reverse T3)

Question 22

Type II

Answer 22

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

Question 23

Which has highest affinity for T4?

Answer 23

TBG

Question 24

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

Answer 24

squamous to cuboidal

Question 25

Inactivated follicles have flattened _____ epithelium

Answer 25

squamous

Question 26

Parafollicular cells (C-cells) secrete

Answer 26

Calcitonin

Question 27

5 cell types thyroid gland

Answer 27

Epithelial Fibroblasts Lymphocytes Adipocytes C-cells

Question 28

Parafollicular cells dont touch

Answer 28

colloid

Question 29

2 precursors for TH

Answer 29

Iodide Thyroglobulin

Question 30

Less than 20micrograms per day of Iodine

Answer 30

Iodine deficiency

Question 31

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

Answer 31

Wolf-Chaikoff Effect. Note: this explains why excess Iodine will shut down hyperthyroidism....

Question 32

What hypothalamic nucleus makes TRH?

Answer 32

PVN

Question 33

What hypothalamic nucleus makes TSH?

Answer 33

Trick question! TRH is from hypothalamus

Question 34

What blocks NIS?

Answer 34

Perchlorate Lithium

Question 35

Half life of T4

Answer 35

7-8 days because binds TBG Binds receptor with LOW affinity

Question 36

T4 to T3 via what enzyme?

Answer 36

De-iodinases (I, II, III)

Question 37

Type 1 De-iodinase removes Iodide from

Answer 37

outer or inner ring

Question 38

Type 2 De-iodinase

Answer 38

outer ring deiodinase

Question 39

What deiodinase will make T4 into active T3?

Answer 39

Type II deiodinase because it removes outer ring iodine. Found in brain, pituitary, placenta, and cardiac tissue.

Question 40

Only deodinase in thyroid gland itself

Answer 40

Type I de-iodinase

Question 41

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

Answer 41

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

Question 42

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

Answer 42

Type II de-iodinase

Question 43

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

Answer 43

Type 3 de-iodinase

Question 44

EVEN THOUGH its a peptide hormone, TH needs to be

Answer 44

bound to TBG in the blood (99%)

Question 45

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

Answer 45

TBG has a higher affinity for TH than albumin!

Question 46

What does estrogen and hepatitis do to TBG?

Answer 46

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

Question 47

Is TH receptor intracellular or extracellular?

Answer 47

Intracellular! Acts like a steroid hormone by affecting transcription

Question 48

Cretinism

Answer 48

Iodine deficiency Small body, mental retardation..

Question 49

T3 effect on heart

Answer 49

Increased SV Increased HR Increased CO

Question 50

Ab against TPO

Answer 50

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

Question 51

GOITER can be the result of

Answer 51

Hashimotos Graves Iodine deficiency

Question 52

Thyroid storm

Answer 52

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

Question 53

Which DECREASES serum cholesterol levels: hypothyroid or hyperthyroid?

Answer 53

Hyperthyroid

Question 54

What does hyperthyroidism do to Beta adrenergic receptors?

Answer 54

upregulates them. thats why you get arryhthmia

Question 55

net cardiac effect of T3?

Answer 55

increased CO and HR