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BRS 4: Endocrinology > 4.3: The thyroid gland > Flashcards

4.3: The thyroid gland Flashcards

1
Q

What glands are embedded in the thyroid

A

Parathyroid glands

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2
Q

What nerve, supplying the vocal cords, runs close to the thyroid gland

A

Left recurrent laryngeal nerve

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3
Q

Embryology of the thyroid gland

A

Midline outpouching from floor of pharynx
Development of thyroglobulin duct
Divided into 2 lobes
Duct disappears leaving for amen caecum
Final position by week 7
Thyroid gland then develops

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4
Q

5 congenital anomalies of the thyroid gland

A

Thyroid agenesis
Lingular thyroid
Retrosternal goitre
Thyroglossal cyst
Thyroglossal fistula

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5
Q

Role of the isthmus

A

Separates 2 lobes of thyroid

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6
Q

What is the pyramid of the thyroid

A

3rd lobe of the thyroid, found in 10-30% of population

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7
Q

Role of parafollicular cells

A

Secrete calcotonin used to produce calcium

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8
Q

What 2 glands are important in calcium metabolism

A

Superior and inferior parathyroid gland

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9
Q

What can happen if the superior or inferior parathyroid glands are damaged during surgery

A

Permanent under active hypoparathyroid glands - hypoparathyroidism

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10
Q

Where is the thyroid hormone made

A

Colloid

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11
Q

How does the thyroid hormone enter the circulation

A

Via capillaries surrounding the follicles

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12
Q

How is thyroid hormone made within the thyroid gland

A

1) TSH from the blood binds to the TSH-R receptor
2) this activates the Na+/I- transporter on the basolateral membrane, stimulating active transport of iodide ions into the follicular cell
3) I- within colloid, oxidases in iodisation to form iodine
4) TSH binding also activates production of thyroglobulin
5) activates thryoperoxidase (enzyme)within cell which enters the colloid with H2O2 and catalyses iodisation reactions
6) once thyroglobulin is iodinated MIT and DIT (mono and id -iodothyrosine) are produced
7)MIT AND DIT join together to form T3 and T4
8) T3 T4 in colloid bound to thyroglobulin,
9) transported out of follicular cell by lysosome
10) T3 T4 enter circulation

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13
Q

What is thyroglobulin and where is it produced

A

Prohormone -glycoprotein which can be iodinated
Produced in the nucleus of the follicular cell

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14
Q

T3 is

A

Active form of thyroid hormone
Provides almost all thyroid hormone activity in target cells

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15
Q

T4 is

A

Tetraiodothyronine
Prohormone converted by deiodinase enzyme into more active triiodothyronine (T3)

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16
Q

What is the main hormone product of the thyroid gland

A

Thyroxine (T4)

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17
Q

What happens to T4 in target tissues

A

Deiodinated to triiodothyronine (T3) - bio active form
Deiodinated in different position to produce reverse T3 (inactive)

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18
Q

Proportions of circulating T3

A

80% from deiodination of T4
20% from direct thyroidal secretion

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19
Q

Half life of T4

A

7-9 days

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20
Q

Half life of T3

A

2 days

21
Q

How are thyroid hormones transported in the blood

A

Bound to plasma proteins
70-80% thyroid-binding globulin TBG
10-15% albumin
prealbumin - aka transthyretin
Only 0.05% T4 and 0.5% T3 is unbound

22
Q

How do T3 and T4 affect gene expression

A

1) enters target tissue cells through respective receptors on cell membrane
2)T4 deiodinated into active T3
3) binds to thyroid hormone receptor - nuclear receptor
4) layers gene expression

23
Q

Actions of thyroid hormone in early life

A

Fetal growth and development - CNS
Untreated congenital hypothyroidism: cretinism

24
Q

How is TSH measured in new borns

A

Heel-prick test

25
Q

Where do foetuses gain their thyroid hormone from whilst in utero

A

Mothers, via placenta

26
Q

4 Actions of thyroid hormone in humans

A

Effects on growth, CNS, GI Reproductive systems
Increases basal metabolic rate
Protein, carb and fat metabolism
Potentiate actions of catecholamines

27
Q

Control of thyroid hormone production

A

1) TRH released from hypothalamus to activate TSH in anterior pituitary gland
2) TSH into circulation and to thyroid gland, stimulates production of T3 and T4
3)Negative feedback at anterior pituitary level and hypothalamic level
4) Somatostatin (prod. In hypothalamus) negatively acts on anterior pituitary
5)large quantities of iodine can inhibit T3/4 production in thyroid

28
Q

What can be used to urgently control thyroid levels

A

Potassium iodide

29
Q

What happens during primary hypothyroidism

A

Thyroxine levels decline
TSH levels climb

30
Q

2 commonest forms of autoimmune thyroid disease

A

Hashimoto’s thyroiditis
Graves’ disease
Presence of one autoimmune disease increases risk of others

31
Q

7 symptoms and signs of hypothyroidism

A

Deepening voice
Depression and tiredness
Cold intolerance
Weight gain with reduced appetite
Constipation
Bradycardia
Eventual myxoedema coma

32
Q

What drug is used to treat hypothyroidism

A

Levothyroxine

33
Q

Proposed mechanism of levothyroxine

A

Same as thyroid action
T4 -> active T3

34
Q

Indications of levothyroxine use

A

Hypothyroidism
Hyperthyroidism- blocking and replacement regimen

35
Q

Dosing of levothyroxine

A

Adjusted according to TSH - aim to get normal range
Common dose 100 micro grams
Most commonly administered orally once daily

36
Q

Potential minor complications of levothyroxine

A

Weight loss
Headache

37
Q

Potential major complications of levothyroxine

A

Heart attack
Rapid HR

38
Q

Alternative therapy for hypothyroidism

A

Combined thyroid hormone replacement

39
Q

Benefits of combined thyroid hormone replacement

A

Combination of T3 and T4 - some improvement in wellbeing

40
Q

Disadvantages of combined thyroid hormone replacement

A

T3 has a shorter half life, so needs to be administered multiple times a day
Complicated symptoms of “toxicity” - palpitations, tremor, anxiety
Often surpresses TSH

41
Q

In hyperthyroidism

A

Thyroid makes too much thyroxine
Thyroxin levels rise
TSH levels drop

42
Q

3 causes of hyperthyroidism

A

Graves’ disease - whole gland smoothly enlarged and whole gland overactive
Toxic multinodular goitre
Solitary toxic nodule

43
Q

What kind of disease is Graves’ disease

A

Autoimmune disease

44
Q

In Graves’ disease

A

Antibodies bind to and stimulate TSH receptor in thyroid
Other antibodies bind to muscles behind eye
Or antibodies stimulate growth of soft tissue of shins

45
Q

In Graves’ disease the binding to and stimulation of TSH receptors in thyroid is called

A

Smooth goitre

46
Q

In Graves’ disease binding of antibodies to muscles behind the eye is called

A

Exophthalamos

47
Q

In Graves’ disease the stimulation of growth of soft tissue in the shins due to antibodies is called

A

Pretibial myxoedema

48
Q

8 symptoms and signs of hyperthyroidism

A

Heat intolerance
Weight loss and increased appetite
Myopathy
Mood swings
Diarrhoea
Tremor of hands
Palpitations
Sore eyes, goitre

BRS 4: Endocrinology (10 decks)

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