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Endocrinology > Thyroid physiology and pathology > Flashcards

Thyroid physiology and pathology Flashcards

1
Q

What hormones does thyroid tissue secrete?

A

Thyroxine (T4)
Tri-iodothyronine (T3)
Calcitonin

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2
Q

What hormone does the parathyroid glands secrete?

A

Parathyroid hormone

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3
Q

What are follicles in thyroid tissue?

A

Colloid spheres enclosed by follicular cells

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4
Q

Which cells secrete calcitonin?

A

Parafollicular C cells

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5
Q

What is colloid in thyroid tissue?

A

Tyrosine-containing, thyroglobulin filled spheres surrounded by follicular cells

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6
Q

Which chemical is taken up by follicular cells to initiate synthesis of T3 & T4?

A

Iodine

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7
Q

What does iodine do to form T3 & T4 once it has been taken into follicular cells?

A

Iodine attaches to tyronine residues on thyroglobulin to form MIT (monoiodotyrosine unit) and DIT (di-iodotyrosine unit)
These then couple to form T3 and T4
MIT + DIT = T3
DIT + DIT = T4

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8
Q

Where is newly formed T3 and T4 stored in the thyroid?

A

In the thyroglobulin

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9
Q

Which is the major biologically active thyroid hormone?

A

T3

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10
Q

Which is the most abundantly produced thyroid hormone?

A

T4

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11
Q

Which organs in the body convert T4 to T3?

A

Liver and kidney

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12
Q

What is the significance of T3 & T4 being lipophilic/hydrophobic?

A

Has to bind to plasma proteins to be transported in blood

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13
Q

What plasma proteins can T3 & T4 bind to for transport?

A

Thyroxine binding globulin (~70%)
Thyroxine binding prealbumin (~20%)
Albumin (~5)

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14
Q

In which form is T3 & T4 biologically active?

A

Unbound (from plasma proteins)

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15
Q

What effect do thyroid hormones have on basal metabolic rate?

A

Increase BMR:
Increase number & size of mitochondria
Increase oxygen use and rates of ATP hydrolysis
Increase synthesis of respiratory chain enzymes

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16
Q

What effect do thyroid hormones have on thermogenesis?

A

Increase thermogenesis

~ 30% temperature regulation due to thyroid hormone thermogenesis

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17
Q

What effect do thyroid hormones have on carbohydrate metabolism?

A

Increase blood glucose due to stimulation of glycogenolysis and gluconeogenesis
Increase insulin-dependent glucose uptake into cells

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18
Q

What effect do thyroid hormones have on lipid metabolism?

A

Mobilise fats from adipose tissue

Increase fatty acid oxidation in tissues

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19
Q

What effect do thyroid hormones have on protein metabolism?

A

Increased protein synthesis

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20
Q

What role do thyroid hormones play in the development of foetal and neonatal brains?

A

Myelinogenesis & axonal growth require thyroid hormones

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21
Q

What effect do thyroid hormones have on growth?

A

Required for growth hormone releasing hormone (GHRH) production and secretion
Required for glucocorticoid-induced GHRH release (permissive action)
GH/somatomedins require presence of thyroid hormone for activity (permissive action)

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22
Q

What is thyroid hormones permissive sympathomimetic action?

A

Thyroid hormones increase the number of beta-receptors, increasing cardiovascular responsiveness as tissues become more sensitive to noradrenaline and adrenaline
Rate and force of cardiac contraction increased

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23
Q

Which hormone is the major stimulant for release of T3 and T4 and from where is it secreted?

A

Thyroid stimulating hormone

Anterior pituitary

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24
Q

Which hormone is the major stimulant for release of thyroid stimulating hormone and from where is it secreted?

A

Thyrotrophin releasing hormone

Hypothalamus

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25
Q

When are thyroid hormone levels naturally highest?

A

Late at night

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26
Q

When are thyroid hormone levels naturally lowest?

A

Morning

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27
Q

What does a thyroid function test in Hashimotos show?

A

Low T3 & T4

High TSH

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28
Q

What does a thyroid function test in Graves disease show?

A

High T3 & T4

Low TSH

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29
Q

What is the onset of graves disease?

A

Gradual

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30
Q

Describe the swelling in Graves disease and does this cause dysphagia?

A

Diffuse enlargement
Painless swelling
Dysphagia only in bulky disease

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31
Q

What is the clinical thyroid status in thyroiditis?

A

Initially hyperthyroid, then hypothyroid

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32
Q

What are the symptoms of thyroiditis?

A

Acute onset
Flu-like symptoms
Tremor often present
No eye disease

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33
Q

What is the most common type of thyroid cancer?

A

Papillary

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34
Q

What is the second most common type of thyroid cancer?

A

Follicular

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35
Q

Between what ages does the risk of developing thyroid cancer in women increase?

A

15-40

36
Q

What thyroid condition is development of papillary thyroid cancer associated with?

A

Hashimoto’s

37
Q

How does papillary thyroid cancer tend to spread?

A

Through lymphatics

38
Q

Where does papillary thyroid cancer spread haematogenously?

A

Bone
Brains
Lung
Liver

39
Q

How does follicular carcinoma tend to spread?

A

Haematogenously

40
Q

What investigations can be done if thyroid cancer suspected?

A

Ultrasound guided fine needle aspiration

May need excision biopsy of lymph node

41
Q

What are some of the clinical predictors of thyroid malignancy?

A 
New thyroid nodule aged 50
Vocal cord palsy
History of radiation exposure to head and neck
Male
Nodule increasing in size
42
Q

What is the preferred treatment option for thyroid cancer?

A

Surgery:
Sub-total thyroidectomy
Total thyroidectomy
Thyroid lobectomy with isthmusectomy

43
Q

Which system is used in Ninewells to determine risk of post-op complications in patients who have just had thyroid cancer surgery?

A 
AMES
A - Age
M - Metastatses
E - Extent of primary tumour
S - Size of primary tumour
44
Q

What is involved in post-op care following thyroid surgery?

A

Calcium levels monitored and replaced if necessary
IV calcium if <1.8mm/L
Patients discharged on T3 and T4

45
Q

When is whole body iodine scanning used?

A

In patients who have undergone total or sub-total thyroidectomy, between 3-6 months post-op

46
Q

When are thyroid replacement medications stopped prior to whole body iodine scanning?

A

T3 - 2 weeks prior to scan

T4 - 4 weeks prior to scan

47
Q

What is Grave’s disease?

A

An autoimmune disease causing hyperthyroidism - antibodies to TSH receptors, thyroglobulin and thyroid peroxisomes

48
Q

Which antibody should be tested for if Grave’s disease suspected and why?

A

Anti-TSH antibody: more specific than peroxisome or thyroglobulin Abs

49
Q

What is the triad of features in Grave’s disease?

A

Hyperthyroidism with diffuse enlargement of the thyroid
Eye changes (exophthalmos)
Pretibial myxoedema

50
Q

What would TFTs show in primary thyroid disease?

A

Hypothyroidism - high TSH and low T3/T4

Hyperthyroidism - low TSH and high T3/T4

51
Q

What would TFTs show in secondary thyroid disease?

A

Hypothyroidism - low TSH and low T3/T4

Hyperthyroidism - high TSH and high T3/T4

52
Q

What is the first marker of hypothyroidism/pre-clinical hypothyroidism?

A

High TSH

T3 & T4 normal

53
Q

What is pretibial myxoedema?

A

Accccumulation of hydrophilic mucopolysaccharides in the ground substance of the dermis and other tissues, resulting in doughy appearance of skin seen classically in the shins: this is seen in Graves disease

54
Q

What are some goitrous causes of hypothyroidism?

A 
Hashimoto's thyroiditis
Iodine deficiency
Drug induced - amiodarone, lithium, IL-2, IFN-a, aminosalicylic acid
Hereditary biosynthetic defects
Maternally transmitted
55
Q

What are some self-limiting causes of hypothyroidism?

A

Following withdrawal of suppressive thyroid therapy
Subacute thyroiditis and chronic thyroiditis with transient hypothyroidism
Postpartum thyroiditis

56
Q

What are some of the non-goitrous causes of hypothyroidism?

A

Congenital developmental defect
Atrophic thyroiditis
Post-ablative (radioiodine, surgery)
Postradiation (e.g. for lymphoma)

57
Q

What is the most common cause of hypothyroidism in the western world?

A

Hashimoto’s thyroiditis/autoimmune thyroiditis

58
Q

What is Hashimoto’s thyroiditis?

A

Autoimmune destruction of the thyroid gland resulting in reduced thyroid hormone production

59
Q

What antibodies are present in Hashimoto’s?

A

Thyroid peroxidase antibodies

60
Q

What are some of the signs and symptoms of hypothyroidism?

A 
Course, sparse hair
Dull expressionless face
Periorbital puffiness
Pale cool 'doughy' skin
Vitiligo
Hypercarotenaemia
Cold intolerance
Pitting oedema
Reduced heart rate
Pericardial effusion
Cardiac dilatation 
Hyperlipidaemia
Decreased appetite
Weight gain
Constipation
Deep hoarse voice
Macroglossia
Obstructive sleep apnoea
Decreased intellectual and motor activities
Depression
Psychosis
Muscle stiffness/cramps
Carpal tunnel syndrome
Menorrhagia
Oligo- or amenorrhoea
Hyperprolactinaemia
61
Q

Why is it dangerous to rapidly restore metabolic rate in hypothyroidism?

A

May precipitate cardiac arrhythmias

62
Q

How frequently should TSH be checked in treated hypothyroidism?

A

2 months after any dose change

Every 12-18 months once stable

63
Q

What is the main treatment in hypothyroidism?

A

Thyroxine

64
Q

When might dose requirement of thyroxine be increased?

A

During pregnancy

65
Q

Who is typically affected by myxoedema coma?

A

Elderly women with long standing but frequently unrecognised or untreated hypothyroidism

66
Q

What are some of the signs and symptoms of hyperthyroidism?

A 
Palpitations
Atrial fibrillation
Cardiac failure (rare)
Tremor
Sweating
Anxiety/nervousness
Irritability
Sleep disturbance
Frequent, loose bowel movements
Lid retraction
Double vision
"Bulging eyes" (Graves)
Brittle, thinning hair
Rapid fingernail growth
Lighter/less frequent periods
Muscle weakness - thighs & upper arms
Weight loss
Increased appetite
Intolerance to heat
67
Q

What does Graves disease show on scintigrapy?

A

Smooth symmetrical goitre

High uptake

68
Q

What is the typical presentation of nodular thyroid disease?

A

Older patient
Insidious onset
Gland may feel nodular

69
Q

What does nodular thyroid disease show on scintigraphy?

A

Assymetrical goitre

High uptake

70
Q

What is sub-acute thyroiditis/de Quervains often associated with?

A

Viral infection - sore throat/fever

71
Q

What do thyroid function tests show in de Quervains?

A

T4 - high in early stage, low in late, then normal

TSH - low in early stage, high in late, then normal

72
Q

What does a scintigraphy scan show in sub-acute thyroiditis?

A

Low uptake

73
Q

What is a thyroid storm?

A

A medical emergency - severe hyperthyroidism

74
Q

What are the signs and symptoms of a thyroid storm?

A

Respiratory and cardiac collapse
Hyperthermia
Exaggerated reflexes

75
Q

What oral medications can be given to treat hyperthyroidism?

A

Carbimazole

Propylthiouracil

76
Q

Which treatment of hyperthyroidism is preferred in pregnancy?

A

Propylthiouracil

77
Q

What treatment can be given to treat the sympathomimetic symptoms of hyperthyroidism?

A

Beta-blockers

78
Q

What are the risks associated with thyroid surgery?

A

Scar
Hypothyroidism
Para-hypothyroidism
Reccurent laryngeal palsy

79
Q

Where are TSH receptors found?

A

The surface of follicular cells

80
Q

What effect does increased production of cAMP have on T3 and T4 levels?

A

Increases production and release of T3 and T4

81
Q

Which patients are typically affected by Hashimoto’s?

A

Middle aged women

82
Q

What are some of the risks associated with Hashimoto’s?

A

Increased risk of developing other auto-immune diseases

Increased risk of developing B cell lymphoma in the affected gland

83
Q

What is a goitre?

A

Any enlargement of the thyroid gland

84
Q

What are thyroid adenomas?

A

Discrete solitary mass composed of neoplastic thyroid follicles, encapsulated by a surrounding collagen cuff

85
Q

Which thyroid carcinoma is derived from C-cells?

A

Medullary carcinoma

Endocrinology (12 decks)

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