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thyroid gland Flashcards

1
Q

what types of hormones are there?

A

peptides
steroids
amines

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2
Q

what type of hormone is thyroid hormone?

A

amine

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3
Q

what are the 2 main types of thyroid hormone?

A

Thyroxine (T4) and Triiodothyronine (T3)

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4
Q

which thyroid hormone is the active form?

A

T3

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5
Q

which thyroid hormone is made in the largest amounts by the thyroid?

A

T4

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6
Q

which lobe of the thyroid is larger?

A

the right lobe

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7
Q

how will enlargement of the thyroid present?

A

right sided lump in the neck

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8
Q

why is the thyroid so good at trapping iodine in a short amount of time?

A

Receives the most blood per unit volume – hence why it’s so good at trapping iodine in a short period of time

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9
Q

what are thyroid follicles?

A

Thyroid follicles are a ring of cells surrounding a ball of fluid in the lumen (colloid)

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10
Q

what type of cells are thyroid cells?

A

cuboidal

columnar when active

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11
Q

name some adaptations of the thyroid follicular cell?

A

• Apex has numerous microvilli extending into the colloid
• Cytoplasm has extensive ER and microsomes
• Predominant Golgi apparatus bc thyroglobulin has a carbohydrate portion
• Numerous lysosomes to break down Tg
- TSHR to receive pituitary signals

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12
Q

what is NIS?

A

thyroidal sodium iodine symporter) to take up iodine from the circulation

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13
Q

what is pendrin?

A

protein to transport iodine into the colloid

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14
Q

what is thyroid peroxidase’s function?

A

oxidising the iodine

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15
Q

what is iodotyrosine dehalogenase 1 (IYD) needed for?

A

recycling iodine

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16
Q

how is thyroid globulin secreted into the follicle lumen?

A

via exocytosis

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17
Q

what is thyroglobulin?

A

a long peptide chain with lots of tyrosine rings

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18
Q

what happens if pendrin is mutated?

A

hypothyroidism and sensory neuron deafness bc it’s also expressed in the semi-circular canals

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19
Q

why does thyroperoxidase do?

A

converts I- to atomic iodine

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20
Q

what is MIT?

A

monoiodotyrosine

when atomic iodine attaches to just 1 tyrosine ring on the thyroglobulin

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21
Q

what is DIT?

A

diiodotyrosine

when atomic iodine attaches to 2 tyrosine rings on the thyroglobulin

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22
Q

how is T3 made?

A

DIT + MIT

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23
Q

how is T4 made?

A

DIT + DIT

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24
Q

how is T4 converted to T3?

A

di-iodinase enzymes

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25
Q

what signalling pathways are activated when TSH binds to TSHR?

A

cAMP or IP3

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26
Q

where is D2 expressed?

A

brain, liver and brown fat

27
Q

what happens to D2 in hypothyroidism?

A

D2 enzyme is upregulated so more T4  T3 – acts as a buffer against changes in T4 levels

28
Q

when is D2 upregulated in brown fat?

A

when you’re cold bc T3 stimulates thermogenesis

29
Q

what proteins do thyroid hormones bind to when in circulation?

A

thyroid binding globulin or albumin

30
Q

what happens to T3 and T4 levels in pregnancy? explain how this happens

A

• In pregnancy, oestrogen levels are higher – causes attachment of side chains to TBG (scialation). Increases the half-life of TBG  binds more thyroid hormone  less free thyroid hormone  hypothyroidism  decreased T4 levels  release more thyroid hormone to compensate

31
Q

what are the locations for receptors?

A

nucleus
cytoplasm
cell surface

32
Q

what happens to the thyroid hormone receptor when thyroid binds?

A
  • When thyroid hormone binds to THR, THR complex falls apart

* Retinoic acid is recruited to make a new heterodimer and allows transcription to be activated

33
Q

what is hyperthyroidism?

A

when the thyroid gland makes too much thyroid hormone

34
Q

what is thyrotoxicosis?

A

the state in which there’s too much thyroid hormone

35
Q

what can cause thyrotoxicosis?

A

Can be caused by hyperthyroidism; damage to the thyroid gland and releasing stored thyroid; taking too much thyroid

36
Q

what are the effects of hyperthyroidism of the cardiovascular system?

A
  • Basal metabolic rate increases  increases heat production
  • More blood is sent to the skin so you get warmer
  • Need to increase CO and therefore increase HR
  • Can lead to tachyarrhythmias
37
Q

how does hyperthyroidism affect metabolism?

A
  • Heat intolerance
  • Increased basal metabolic rate
  • Increased appetite bc nutrients needed to supply fuel
  • Need to break down protein and lipids to get this fuel
  • Leads to weight loss and myopathy (mostly felt in larger proximal muscles – cant stand up in a chair)
38
Q

what is the effect of hyperthyroidism on diabetes?

A

o Increased insulin turnover
o Increased gluconeogenesis
o Reduced insulin secretion

39
Q

what effect does hyperthyroidism have on the nervous system?

A
  • Nervousness
  • Seizures – lower seizure threshold in people with epilepsy
  • Hyperphagia – increased hunger
40
Q

what effect does hyperthyroidism have on the skin?

A

Plummer’s nails

Pretibial myxoedema

41
Q

what is pretibial myxoedema?

A

a swollen rash you get in Graves disease

42
Q

what effect does hyperthyroidism have on the GI tract?

A

• Increased appetite, weight loss, increased motility, transaminitis, constipation

43
Q

what effect does hyperthyroidism have on bones?

A
  • Accelerated osteoclast activity – break down bone for fuel  transient hypercalcaemia
  • Osteoperosis in long term hyperthyroidism
44
Q

what haematological effects does hyperthyroidism have?

A

pernicious anaemia, B12 deficiency (only in AITD)

45
Q

what effect does hyperthyroidism have on reproduction?

A

oligomenorrhoea, gynecomastia (bc testosterone is developing into oestrogen more rapidly), erectile dysfunction

46
Q

what is Grave’s disease characterised by?

A
  • Characterised by antibodies against TSHR

* T-lymphocytes commonly seen

47
Q

why does grave’s disease affect the eyes?

A

Retroorbital fibrocytes express TSH-receptor

48
Q

what are risk factors for Grave’s disease?

A

HLA status (imp bc it’s an autoimmune disease), infection, stress, female

49
Q

how does Grave’s disease present in men?

A

Men normally have a severe phenotype that’s harder to treat with anti-thyroid drugs

50
Q

what are other causes of thyrotoxicosis?

A

toxic multinodular goitre
toxic adenoma
Excess iodine, Amiodarone, HCG, Thyroiditis, Struma ovarii, TSHoma, Hamburger thyrotoxicosis

51
Q

how does TSHR cause thyrotoxicosis?

A
  • TSHR in one cell mutates and becomes constitutively active
  • Stimulating the TSHR causes hyperplasia so the cell divides
  • Mutated TSHR divides
52
Q

how do you diagnose a toxic adenoma?

A

Technetium or iodine uptake scans

53
Q

how do you treat a toxic adenoma?

A

o Thionamide drugs – Propylthiouracil or Carbimazole
 Start with 18 months of C then stop
 If it doesn’t work then they either need long term C or different more definitive treatment
o Radioactive Iodine I-131
o Thyroidectomy

54
Q

how effect is Carbimazole?

A

Cures 50% of women and 20% of men

55
Q

what effect does hypothyroidism have on the skin?

A
  • Skin becomes rlly dry
  • Hair becomes dry
  • Myxoedema in the skin
  • Hyaluronic acid accumulation
  • Hypercarotenaemia
  • Reduced sweat and sebum
  • Wounds heal slowly
  • Capillary fragility
56
Q

what effect does hypothyroidism have on the cardiovascular system?

A
  • Reduced cutaneous ciculation = sensitivity to cold
  • Sinus bradycardia
  • LDL cholesterol up
  • J waves of hypothermia
57
Q

what effect does hypothyroidism have on the GI tract?

A

reduced appetite and constipation (bc reduced peristalsis)

58
Q

what effect does hypothyroidism have on nervous system. muscle and bone?

A
  • Impaired fetal brain development
  • Dementia
  • Slow relaxing reflexes
  • Growth retardation
59
Q

what effect does hypothyroidism have on the renal system?

A

reduced GFR, mild hyponatremia

60
Q

what haematological effects does hypothyroidism have?

A

normochromic normocytic anaemia
• decreased red cell mass and less EPO norm norm anaemia
• B12 def macrocytic
• menorrhagia and achloryhydria - microcytic

61
Q

what endocrine effects does hypothyroidism have?

A

delayed puberty, reduced libido, erectile dysfunction

62
Q

what effects does hypothyroidism have on metabolism?

A

reduced basal metabolic rate, decreased GLUT4 stimulation

63
Q

what are the causes of hypothyroidism?

A

• Hashimoto’s disease; Endemic goitre; Lithium; Cabbage; Infiltrative diseases; Pendred’s syndrome; Hypopituitarism

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