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Endocrinology > Thyroid hormones > Flashcards

Thyroid hormones Flashcards

1
Q

What cells make up the thyroid gland?

A

Follicular cells - simple cuboidal epithelial cells + parafollicular C cells

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2
Q

Which nucleus of the hypothalamus influences thyroid hormone production?

A

Paraventricular nucleus of the hypothalamus secretes thyroid releasing hormone

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3
Q

Where is TRH released from?

A

Paraventricular nucleus

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4
Q

What does TRH do?

A

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

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5
Q

Where is TSH produced from?

A

Thyrotropes in the anterior pituitary gland

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6
Q

Which hormones does TRH stimulate?

A

TSH and Prolactin

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7
Q

What kind of hormone is TRH?

A

A peptide hormone

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8
Q

What causes the synthesis of thyroglobulin?

A

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

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9
Q

How is iodide transported into follicular cells of the thyroid?

A

By iodide/sodium transporters

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10
Q

What is the function of thyroid peroxidase?

A

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

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11
Q

What is the alternative name for T4?

A

Thyroxine

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12
Q

What is thyroxine binding globulin?

A

A protein secreted by the liver that transports T3 and T4

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13
Q

What is the difference between thyroxine binding globulin and thyroglobulin?

A

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

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14
Q

TRH is released by…

A

The paraventricular nucleus of the hypothalamus

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15
Q

TSH is released by…

A

Anterior pituitary gland

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16
Q

TSH stimulates…

A

follicular cells of the thyroid gland to produce thyroglobulin

17
Q

Thyroperoxidase causes…

A

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

18
Q

When does thyroid gland development begin in embryology?

A

By day 24

19
Q

when is thyroid development complete in embryology?

A

5-6th week

20
Q

What are C cells derived from?

A

4th pharyngeal pouch

21
Q

Where does the isthmus of the thyroid gland lie?

A

Anterior to tracheal rings 2-4

22
Q

What is the main blood supply to the thyroid gland?

A

Inferior thyroid artery

23
Q

Where is thyroxine binding globulin made?

A

Liver

24
Q

How is thyroid hormone active in cells?

A

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

25
Q

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

A

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

26
Q

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

A

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

27
Q

What is the impact of thyroid hormone on the liver?

A

Glycogenolysis
Gluconeogenesis
Increase uptake of LDL from the blood

28
Q

What happens to thyroid binding globulins in pregnancy?

A

They increase

29
Q

what happens to total T4 and T3 levels in pregnancy?

A

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

30
Q

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

A

Lower in pregnancy

31
Q

How do free T3 and T4 levels change during pregnancy?

A

They drop

32
Q

What happens to TSH levels in pregnancy?

A

They decrease

33
Q

Why do TSH levels reduce in pregnancy?

A

HCG levels increase (HCG is partially thyrotrophic)

34
Q

In hyperemesis, what is the thyroid function usually like?

A

High free T3 and T4, low TSH

This is thought to be related to the thyrotropic properties of Beta HCG

35
Q

What is the effect of Beta HCG on thyroid function?

A

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

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