Thyroid hormones

Question 1

What cells make up the thyroid gland?

Answer 1

Follicular cells - simple cuboidal epithelial cells + parafollicular C cells

Question 2

Which nucleus of the hypothalamus influences thyroid hormone production?

Answer 2

Paraventricular nucleus of the hypothalamus secretes thyroid releasing hormone

Question 3

Where is TRH released from?

Answer 3

Paraventricular nucleus

Question 4

What does TRH do?

Answer 4

TRH stimulates the thyrotropes to secrete thyroid stimulating hormone (TSH)

Question 5

Where is TSH produced from?

Answer 5

Thyrotropes in the anterior pituitary gland

Question 6

Which hormones does TRH stimulate?

Answer 6

TSH and Prolactin

Question 7

What kind of hormone is TRH?

Answer 7

A peptide hormone

Question 8

What causes the synthesis of thyroglobulin?

Answer 8

TSH activation of G protein linked receptors on the follicular cells of the thyroid gland

Question 9

How is iodide transported into follicular cells of the thyroid?

Answer 9

By iodide/sodium transporters

Question 10

What is the function of thyroid peroxidase?

Answer 10

Converts iodide to iodine (oxidation of iodide to I2) and then iodinates the tyrosine amino acids of thyroglobulin forming T4 (thyroxine) and T3 (triiodothyronine) = thyroid hormone

Question 11

What is the alternative name for T4?

Answer 11

Thyroxine

Question 12

What is thyroxine binding globulin?

Answer 12

A protein secreted by the liver that transports T3 and T4

Question 13

What is the difference between thyroxine binding globulin and thyroglobulin?

Answer 13

TBG - protein that transports T3 and T4 in blood
Thyroglobulin - a protein formed by thyroid cells under stimulation by TSH, which is iodinised by TPO enzymes to form T3 and T4 hormones

Question 14

TRH is released by…

Answer 14

The paraventricular nucleus of the hypothalamus

Question 15

TSH is released by…

Answer 15

Anterior pituitary gland

Question 16

TSH stimulates…

Answer 16

follicular cells of the thyroid gland to produce thyroglobulin

Question 17

Thyroperoxidase causes…

Answer 17

oxidation of iodine, iodination of tyrosine amino acids on thyroglobulin and coupling to form T3 and T4

Question 18

When does thyroid gland development begin in embryology?

Answer 18

By day 24

Question 19

when is thyroid development complete in embryology?

Answer 19

5-6th week

Question 20

What are C cells derived from?

Answer 20

4th pharyngeal pouch

Question 21

Where does the isthmus of the thyroid gland lie?

Answer 21

Anterior to tracheal rings 2-4

Question 22

What is the main blood supply to the thyroid gland?

Answer 22

Inferior thyroid artery

Question 23

Where is thyroxine binding globulin made?

Answer 23

Liver

Question 24

How is thyroid hormone active in cells?

Answer 24

Thyroxine (T4) is deionised at 5 prime carbon to form active T3

Question 25

What does active T3 do on a molecular level in cells?

Answer 25

Causes the production of sodium/potassium/ATPase pumps, which leads to increased metabolic activity within the cell

Question 26

What is the impact of thyroid hormone on blood glucose levels?

Answer 26

Hyperglycaemia - They increase by release of glucose from glycogen stores in the liver and stimulate gluconeogenesis

Question 27

What is the impact of thyroid hormone on the liver?

Answer 27

Glycogenolysis Gluconeogenesis Increase uptake of LDL from the blood

Question 28

What happens to thyroid binding globulins in pregnancy?

Answer 28

They increase

Question 29

what happens to total T4 and T3 levels in pregnancy?

Answer 29

They increase due to an increase in thyroid binding globulins, therefore free T3 and T4 must be measured

Question 30

What are TSH levels in pregnancy compared to TSH outside of pregnancy?

Answer 30

Lower in pregnancy

Question 31

How do free T3 and T4 levels change during pregnancy?

Answer 31

They drop

Question 32

What happens to TSH levels in pregnancy?

Answer 32

They decrease

Question 33

Why do TSH levels reduce in pregnancy?

Answer 33

HCG levels increase (HCG is partially thyrotrophic)

Question 34

In hyperemesis, what is the thyroid function usually like?

Answer 34

High free T3 and T4, low TSH | This is thought to be related to the thyrotropic properties of Beta HCG

Question 35

What is the effect of Beta HCG on thyroid function?

Answer 35

Beta HCG is thyrotropic and therefore raises thyroid hormone levels in early pregnancy causing a fall in TSH