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BRS Y1 > Week 3- The Thyroid Gland > Flashcards

Week 3- The Thyroid Gland Flashcards

1
Q

How many lobes does the thyroid have?

A

Usually 2, some people have 3 (10-15% of people have a third lobe called the pyramid)

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2
Q

What is the gap that joins the 2 lobes of the thyroid?

A

Isthmus

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3
Q

What is the thyroid comprised of?

A

Follicles

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4
Q

What glands are embedded in the thyroid?

A

Parathyroid

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5
Q

What nerve associated with the thyroid supplies the vocal chords?

A

Left recurrent laryngeal nerve

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6
Q

What are the 2 glands in the thyroid that are important for calcium metabolism?

A

Inferior and superior parathyroid glands

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7
Q

What part of the cell are the thyroid hormones made?

A

In the colloid

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8
Q

What are the 2 thyroid hormones called?

A

T3 (triiodothyronine) and T4 (thyroxine)

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9
Q

Out of T3 and T4, which is active and which is inactive

A

T3 is active

T4 is inactive

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10
Q

What 2 molecules couple to form T3?

A

Monoiodotyrosine and diiodotyrosine

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11
Q

What 2 molecules couple to form T4?

A

2 molecules of triiodothyronine

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12
Q

What is the main hormone product of the thyroid gland?

A

T4

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13
Q

How is T4 activated?

A

It is deiodinated to T3 in target tissues

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14
Q

What is reverse T3?

A

A molecule produced when T4 is deiodonated in a different position to produce an inactive molecule

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15
Q

What enzyme converts T3 to T4?

A

Deiodinase enzyme

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16
Q

How do thyroid hormones affect cells?

A

They bind to receptors and change gene expression

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17
Q

Why is the mothers thyroid hormone status important in pregnancy?

A

The foetus gets its thyroid hormone from the mother so essential for growth and development

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18
Q

What is cretinism?

A

Untreated congenital hypothyroidism

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19
Q

How is congenital hypothyroidism measured in babies?

A

Heel prick test

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20
Q

What are some of the main actions of the thyroid hormone?

A

It increases basal metabolic rate, increases cardiac output, affects GI, CNS, reproductive system

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21
Q

What is the half life of T3

A

2 days

22
Q

What is the half life of T4?

A

7-9 days

23
Q

A lot of which molecule inhibits T3/T4 production?

A

Iodide

24
Q

Are thyroid disorders more common in women or men, by how much and why?

A

In women by a 4:1, due to autoimmunity

25
Q

Are over or under active thyroids more common?

A

Neither they’re the same

26
Q

What happens in hypothyroidism and how does it arise?

A

Thyroxine levels decline and TSH levels climb, due to autoimmune damage

27
Q

What are the 2 main common thyroid disease?

A

Hashimoto’s thyroiditis (hypothyroidism)

Graves’ disease (hyperthyroidism)

28
Q

What are common symptoms of hypothyroidism?

A 
Fatigue
Depression 
Deep voice
Cold intolerance
Weight gain
Reduced appetite 
Constipation 
Bracycardia
Eventual myxedema coma
29
Q

What medicine is given to treat hypothyroidism?

A

Levothyroxine

It can also treat hyperthyroidism sometimes

30
Q

What is the common dose of levothyroxine?How is it administered?

A

100 micrograms

Administered orally

31
Q

What is common thyroid hormone replacement?

A

Giving a mix of T3 as well as T4

32
Q

What happens in hyperthyroidism?

A

Thyroxine levels rise

TSH levels drop

33
Q

What are the 3 main causes of hyperthyroidism?

A

Graves’ disease (whole gland smoothly enlarged and whole gland overactive)

Toxic multinodular goitre

Solitary toxic nodule

34
Q

What is the mechanism of action in Graves’ disease?

A

Antibodies bind to and stimulate TSH receptors in the thyroid causing a smooth goitre

35
Q

What happens in Graves’ disease when antibodies bind to muscles behind the eye?

A

Exophthalmos- the eyes bulge and you can see the whites around the eye

36
Q

What happens in Graves’ disease when antibodies bind to soft growth tissue of shins?

A

Pretibial myxoedema

37
Q

What are common symptoms of hyperthyroidism?

A 
Heat intolerance
Weight loss with increased appetite 
Myopathy
Mood swings
Diarrhea 
Tremor of hands
Palpitations
Sore eyes 
Goitre
38
Q

What 2 cell types are present in thyroid follicles?

A

Follicular cells and colloid cells

39
Q

Describe the embryology of the thyroid gland

A

Originates from the base of the tongue (floor of the pharynx)

Development of thyroglossal duct

Divides into 2 lobes

Duct disappears leaving the foramen cæcum

Thyroid gland then develops

40
Q

Where does circulating T3 come from?

A

80% from deiodination of T4

20% from direct thyroidal secretion

41
Q

How are thyroid hormones transported in the blood?

A

They are bound to plasma proteins (99% of the time)

42
Q

What are the 3 main plasma proteins that transport thyroid hormones?

A

Thyroid binding globulin
Albumin
Prealbumin/ transthyretin

43
Q

How is thyroid hormone production controlled?

A

The negative feedback loop prevents excess production as T3/T4 production switches off TRH in hypothalamus (indirectly via switching off TSH) and TSH production in the anterior pituitary (directly)

44
Q

What are potential minor complications of taking levothyroxine?

A

Weight loss and headache

45
Q

What are potential major complications of taking levothyroxine?

A

Heart attack and rapid heart rate

46
Q

What is thyroglobulin, where is it produced and what special property does it have?

A

It is the prohormone produced in the anterior pituitary gland that has a thymine residue that can be iodised. It allows the synthesis of T3 and T4 in the presence of thyroperoxidase

47
Q

Describe the pathway for T3/T4 synthesis in the thyroid gland

A

TSH is produced by the anterior pituitary gland and binds to TSH receptors on follicular cells

Iodide is transported into the follicular cell via sodium iodine receptor and then to the colloid

Iodide is oxidized to iodine

TSH binding also starts production of thyroglobulin (a proenzyme that has a thymine residue that can be iodised)

Thyroperoxidase enzyme is also activated by TSH binding and travels to the colloid where it catalyses iodination reactions

Iodination of thyroglobulin allows synthesis of T3 and T4 (that are still bound to thyroglobulin)

Protein bound T3 and T4 travel back to follicular cells where peptide bonds are broken and T3/T4 are released into the bloodstream

48
Q

What molecule is essential in the synthesis pathway of T3/T4?

A

Iodide (but it must be oxidized to iodine in the synthesis pathway)

49
Q

How does TRH from the hypothalamus reach the anterior pituitary?

A

It is released into the medial leminence and as the vessels are leaky travels via portal circulation

50
Q

What does ‘primary’ in primary hypothyroidism mean?

A

That it is a problem with the gland

51
Q

What is menorrhagia and what thyroid condition is it a common feature of?

A

Heavy peroids- a common feature of hypothyroidism

52
Q

How much time after initial levothyroxine prescription is the dosage checked and how is it checked?

A

Checked after 6/8 weeks

If the dose is too high TSH levels will be too low

If the dose is too low TSH levels will be too high

BRS Y1 (52 decks)

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