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Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Parafollicular cells

A

Occasional scattered C cells

  • Slightly larger cells with clearer cytoplasm
  • Secrete calcitonin
  • Lower serum Ca but in practise is of little significance
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2
Q

Causes of Hyperthyroidism

A 
Graves disease
Hyperfunctioning nodules/tumours
Thyroiditis
TSH secreting pituitary adenoma (rare)
Ectopic production (struma ovarii)
Factitious (exogenous intake)
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3
Q

Struma ovarii

A

Literally a goitre of the ovary, containing thyroid tissue

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4
Q

Palpation thyroiditis

A

Palpation thyroiditis refers to the development of thyroid inflammation due to mechanical damage to thyroid follicles. This can occur by vigorous repeated palpation (as with thyroid examination) or surgical manipulation (as can occur with radical neck dissection)

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5
Q

Subacute lymphocytic thyroiditis

A

Subacute lymphocytic thyroiditis features a small goiter without tenderness. This condition tends to have a phase of hyperthyroidism followed by a return to a euthyroid state, and then a phase of hypothyroidism, followed again by a return to the euthyroid state. The time span of each phase can vary; however, each phase usually lasts 2-3 months
Can be diagnosed by radioactive iodine uptake test
During hyperthyroid period, uptake is suppressed. During hypothyroid it is incresased

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6
Q

de Quervains Thyroiditis

A

Hyperthyroid
Hypothyroid
Euthyroid

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7
Q

Distinguishing between subacute thyroiditis and Graves disease

A

The clinical presentation during the hyperthyroid phase can mimic those of Diffuse Toxic Goiter or Graves’ disease. In such cases, a radionuclide thyroid uptake and scan can be helpful, since subacute thyroiditis will result in decreased isotope uptake, while Graves’ disease will generally result in increased uptake. Distinguishing between these two types of disease is important, since Graves’ disease and Diffuse Toxic Goiter can be treated with radioiodine therapy, but subacute thyroiditis is usually self-limited and is not treated with radioiodine.

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8
Q

Riedel’s Thyroiditis

A

Riedel’s thyroiditis is characterized by a replacement of the normal thyroid parenchyma by a dense fibrosis

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9
Q

Who does Grave’s disease tend to affect?

A

F:M 10:1

Age 20-40

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10
Q

When might you see antibodies to TSH receptor, thyroid peroxisomes and thyroglobulin?

A

Grave’s Disease

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11
Q

Anti-TSH receptor antibodies

A

Thyroid stimulating immunoglobulin
Relatively specific (unlike peroxisome and thyroglobulin abs)
Thyroid growth stimulating immunoglobulin
TSH binding inhibitor immunoglobulins
May explain episodes of hypofunction

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12
Q

Triad of features of Grave’s disease

A

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

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13
Q

Why do you get eye changes in hyperthyroidism?

A

The eye changes result from fibroblasts etc expressing TSH receptors

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14
Q

Hashimoto’s Thyroiditis

A

Affects middle aged women
Associated with other AI disease
Associated with HLA – DR3 and DR5

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15
Q

Causes of hypothyroidism

A

Hashimoto’s Thyroiditis
Iodine deficiency, drugs, post therapy (surgery, 131 I, irradiation)
Congenital abnormalities
Inborn errors of metabolism

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16
Q

Which has a longer half life, T3 or T4?

A

T4.

T4 is also the major form of thyroid hormone in the blood

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17
Q

People most likely to develop Hashimoto’s thyroiditis?

A

F:M 10-20:1

Ages 45-60

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18
Q

Gene Polymorphisms associated with Hashimoto’s Thyroiditis?

A

CTLA-4

PTPN-22

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19
Q

What may preceded hashimoto’s thyroiditis?

A

Hashitoxicosis

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20
Q

What does hashimotos thyroiditis put you at a greater risk of?

A

Other autoimmune diseasea

Increased risk of developing B cell non- Hodgkin’s lymphoma in affected gland

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21
Q

What are goitre’s often caused by?

A

Lack of iodind

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22
Q

Diffuse Goitre

A

Endemic - >10% population affected
Sporadic – F > M, puberty and young adults
Ingestion of substances limiting T3/T4 production
Inborn errors of metabolism (dyshormonogenesis)
Most cases – cause unknown
Usually euthyroid – present with mass effects
T3 / T4 normal but TSH high or upper limit of normal
In children dyshormonogenesis may cause cretinis

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23
Q

T3/T4 and TSH levels in diffuse goitre?

A

T3/T4 levels normal

TSH high or upper limit of normal

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24
Q

Multi-nodular goitre differential diagnosis?

A

Thyroid neoplasm

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25
Q

Multi-nodular goitre

A

Evolution from long standing simple goitre
Recurrent hyperplasia and involution
Enlargement can be impressive
DDx thyroid neoplasm
Variation of response of follicular cells to external stimuli
Mutations of TSH signaling pathway.
Rupture of follicles, haemorrhage, scarring, calcification
Mass effects
Cosmetic
Airway obstruction, dysphagia, compress vessels
May develop autonomous nodule – hyperthyroid
10% after 10 years
Low risk of malignancy (<5% but not 0)

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26
Q

What does the thyroid produce?

A

Tri-iodothyronine
Thyroxine
Calcitonin

27
Q

What cells secrete calcitonin?

A

Parafollicular C cells

28
Q

Structure of the thyroid gland tissue

A

Follicular cells
Colloid – tyrosine-containing thyroglobulin filled spheres enclosed by follicular cells
Parafollicular cells

29
Q

What do the follicular cells make?

A

T3, T4 and thyroglobulin

30
Q

Which organs can convert T4 into T3?

A

The liver and the kidney

31
Q

What type of receptors does T3 bind to?

A

Nuclear receptors

32
Q

Are T3 and T4 lipophilic? And if so what do they bind to?

A

Yeah
thyroxine binding globulin (TBG ~70%)
thyroxine binding prealbumin (TBPA ~20%)
Albumin (~5%)

33
Q

Plasma protein which binds the most T3 and T3

A

Thyroxine binding globulin (70%)

34
Q

What is TTR?

A

Transthyretin, a T4 carrier

35
Q

Phenytoin

A

Anti-epileptic

Can cause decrease in TBG

36
Q

Clofibrate

A

Cholesterol lowering drug

Can cause increased TBG

37
Q

Thryoid hormone effects on carbohydrate metabolism

A

Increases blood glucose due to stimulation of gluconeogenesis and glycogenolysis

38
Q

Thyroid hormone effects on protein metabolism

A

Increases protein synthesis

39
Q

Thyroid hormone effects on lipid metabolism

A

Mobilises fats from adipose tissue

Increases fatty acid oxidation in tissues

40
Q

Thyroid hormone and growth

A
  • Thyroid hormone needed for production and secretion of growth hormone releasing hormone (GHRH)
  • Thyroid hormone needed for glucocorticoid stimulated release of GHRH
  • Growth hormone/somatomedins require thyroid hormone for activity (permissive action)
41
Q

Thyroid hormone and foetal/neonatal brain development

A

Thyroid hormone needed for myelinogenesis and axonal growth

42
Q

Thyroid hormone and normal CNS activity

A

Hypothyroidism - slow intellectual functions

Hyperthyroidism – nervousness, hyperkinesis & emotional lability

43
Q

Thyroid hormone Sympathomimetic action

A

Permissive Sympathomimetic action

  • Thyroid hormones increase responsiveness to adrenaline & sympathetic NS neurotransmitter, noradrenaline, by increasing numbers of receptors
  • Cardiovascular responsiveness also increased due to this effect – increased force and rate of contraction of heart
44
Q

Thyroid hormone regulation:

  • Low temperature
  • Stress
  • Circadian rhythm
A
  • Low temperatures - In babies and young children, exposure to cold environments stimulates TRH release which stimulates TSH release and so increases T3 &T4 release from thyroid
  • Stress – inhibits TRH & TSH release
  • Circadian rhythm – thyroid hormones highest late at night, lowest am
45
Q

Thyroid stimulating immunoglobulin

A

Hyperthyroidism - Grave’s disease

Autoimmune disease – Thyroid stimulating immunoglobulin (TSI) acts like TSH but unchecked by T3 & T4

46
Q

Which 2 hormones can lead to insulin resistance in mothers?

A

Human placental lactogen
Progesterones

(insulin resistance may lead to raised blood glucose if predisposed and then gestational diabetes.)

47
Q

Which trimester does gestational diabetes develop?

A

Third trimester

48
Q

In which trimester does the baby begin to make its own insulin?

A

Third trimester (it is a major growth factor)

49
Q

How much folic acid would you give to mothers with gestational diabetes?

A

5mg

50
Q

If a woman has gestational diabetes, what test should you carry out SIX WEEKS AFTER BIRTH to ensure resolution

A

Glucose tolerance test ;)

You should also do an annual fasting glucose

51
Q

hCG levels in hyperemesis gravidarum?

A

hCG HIGH

50-60% have abnormal TSH/fT4

52
Q

What hormone increases TBG?

A

Oestrogen

53
Q

Where is T4 converted to T3?

A

Liver and kidneys

54
Q

Why do thyroxine hormones bind to protein and which proteins do they bind to?

A

T3 &T4 are hydrophobic/ lipophillic - so bind to plasma proteins
thyroxine binding globulin (TBG ~70%)
thyroxine binding prealbumin (TBPA ~20%)
Albumin (~5%)

55
Q

Which hormones are required for production and secretion of GHRH?

A

Thyroid hormones

56
Q

Glucocorticoid-induced GHRH release also dependent on which hormones?

A

Thyroid hormones

57
Q

Myelinogenesis & axonal growth of the foetal and neonatal brain require which hormones?

A

Myelinogenesis & axonal growth

58
Q

Thyroid hormones and effect on responsiveness to adrenaline and noradrenaline?
And effect on the heart?

A

Thyroid hormones increase responsiveness to adrenaline & sympathetic NS neurotransmitter, noradrenaline, by increasing numbers of receptors

cardiovascular responsiveness also increased due to this effect – increased force and rate of contraction of heart

Pharmacology note
Need to use beta-blocker e.g. PROPRANOLOL to treat symptoms in initial stages on therapy for hyperthyroidism

59
Q

Thyroid hormone regulation and stress?

A

inhibits TRH & TSH release

60
Q

Low temperatures and thyroid regulation?

A

In babies and young children, exposure to cold environments stimulates TRH release which stimulates TSH release and so increases T3 &T4 release from thyroid

61
Q

Primary or secondary thyroid dysfunction is associated with goitre?

A

Primary (gland) failure – may be associated
with enlarged thyroid (goitre)
Secondary to TRH or TSH (no goitre)
Lack of iodine in diet (may be associated with goitre

62
Q

In adults – Myxoedema – puffy face, hands & feet

Babies - Cretinism – dwarfism & limited mental functioning due to deficiency of thyroid hormones present at birth

A

Hypothyroidism

63
Q

Thyroid stimulating immunoglobulin?

A

Autoimmune disease – Thyroid stimulating immunoglobulin (TSI) acts like TSH but unchecked by T3 & T4
Exophthalmos – bulging eyes due to water retaining carbohydrate build up behind eyes
Goitre –enlarged thyroid gland

Endocrinology (30 decks)

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