Thyroid Flashcards by Shirley Ross

descirbe primary thyroid disease

disease affecting thyroid gland itself

autoimmune thyroid disease most common

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describe scondary thyroid disease

hypothalmic or pituitary disease

no thyroid gland pathology

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what is TSH

thyroid stimulating hormone

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where is TSH released?

thyrotroph cells in anterior pituitary

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TSH is released in response to what?

thyrotropin releasing hormone TRH

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TSH is also called what?

thyrotropin

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release of TSH results in what?

production of T3 and T4

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99% of T4 and T3 is bound to what?

plasma proteins

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what plasma proteins do T3 and T4 bind to?

Thyroxine Binding Globulin (TBG)- 70%

Transthyretin (TTR)- 20%

Albumin- 5%

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what levels of free T3/4 and TSH would be seeen in primary hypothyroidism

free T3/4 low

TSH high

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what levels of T3/4 and TSH would be seen in primary hyperthyroidism?

free T3/4 high

TSH low

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what si the difference between primary and secondary thyroid disease?

primary- problem with thyroid gland iself

secondary- problem with hypothalmus/pituitary

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what levels of T3/4 and TSH would be seen in secondary hypothyroidism?

low free T3/4

TSH low (or normal)

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what levels of free T3/4 and TSH would be seen in secondary hyperthyroidism?

free T3/4 high

TSH high (or normal)

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define myxoedema

severe hypothyroidism

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pretibial myxoedema is a rare clinical sign in which autoimmune thyroid condition?

Graves disease

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graves disease results in hypo/hyperthyroidism?

hyperthyroidism

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what are soem goitrous causes of hypothyroidism?

hashimotos thyroiditis

iodine deficiency

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what are some non-goitrous causes of hypothyroidism?

atrophic thyroiditis

post radiotherapy

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what would be a self-limiting cause of hyperthyroidism?

withdrawl of antithyroid drugs

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describe hashimotos thyroiditis?

autoimmune destruction of thyroid gland and reduced thyroid hormone productioin

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hashimotos is characterised by which antibodies?

antibodies against thyroid peroxidase (TPO)

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what is seen microscopically in hashimotos?

T cell infiltrate

inflammation

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what is prescribed to people with hypothyroidism?

levothyroxine

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how soon should TSH levels be checked once started on thyroxine in hypothyroidism?

2 months after any dose change

once established how often should TSH be checked?

12-18 months

when should levothyroxine be taken to try and prevent problems with absorption?

before eating before any other medications

what is thyrotoxixosis?

the state when you have too much thyroxine

what is hyperthyroidism?

condition where you get thyrotoxic due to thyroid gland pathology

how cna graves disease affect your bones?

osteoporosis

over 90% of people with Graves will have detectable levels of which antibody?

**TRAb-** TSH receptor antobody

severe hyperthyroidism is referred to as what?

thyroid storm

thyroid storm is common in those with which autoimmune condition?

graves

what is the treatment of hyperthyroidism?

antithyroid drugs

how do antithyroid drugs work?

inhibit TPO therby blocking thyroid hormone synthesis

what is the first line antithyroid drug used in hyperthyroidism?

carbimazole

what is a side effect of antithyroid drugs?

agranulocytosis

when is the risk of angranulocytosis greatest when prescribed an antithyroid drug?

first 6 weeks

which B blocker is commonly used in hyperthyroidism?

propanolol

in which group of patients is the use of radioiodine contraindicated in hyperthyroidism?

contraindicated in pregnancy

what are the risks with surgery in hyperthyroidism?

recurrent laryngeal nerve palsy hypothyroidism hypoparathyroidism

what is thyroiditis?

inflammation of thyroid

what is non-thyroidal illness also known as?

sick euthyroid syndrome

what does non-thyroidal illness refer to?

impact of illness e.g severe infection- TSH supressed then rises again with recovery

thyroid gland tissue secretes what?

thyroxine T4 tri-iodothyronine T3 calcitonin

which imaging technique is particulary useful when investigating the thyroid?

iodine uptake scan

an iodine uptake scan will appear darker in hypo/hyper thyroidism?

**hyper**thyroidism

which cells secrete calcitonin?

parafollicular C cells

what is required for the synthesis of thyroid hormones?

iodine

iodine is taken up by which thyroid cells?

follicle cells

iodine attaches to what in order to form MIT and DIT?

iodine attaches to **tyrosine residues on thyroglobulin**

coupling of MIT + DIT forms what thyroid hormone?

coupling of 2 DIT forms what?

T3 and T4 are stored where?

colloid thyroglobulin

how long can T3 and T4 be stored for?

weeks to months

which thyroid hormone is the most abundant?

which thyroid hormone is the most biologically active?

which form of thyroid hormone is biologically active bound/unbound?

unbound

T3 acts on what kind of receptor?

nuclear receptor

why do T3 and T4 bind to plasma proteins?

hydrophobic lipophilic

metabolic state correlates more with the free T3 and T4/ the total conc in plasma?

the free T3 and T4

thyroid hormones target virtually every tissue to alter what two things?

gene transcription protein synthesis

what are the physiological effect sof thyroid hormones?

metabolism growth & development reproduction behaviour

thyroid hormones inc/dec basal metabolic rate

increase metabolic rate

how do thyroid hormones increase metabolic rate?

inc no & size metabolic rate inc oxygen use and rates of ATP hydrolysis

thyroid hormones inc/dec thermogenesis?

**incerease** thermogenesis

what percentage of temperature regulation is due toi thyroif hormones?

30%

what are the metabolic effects of thyroid hormones?

inc blood glucose inc fatty oxid in tissues inc protein synthesis

whoch growth hormone requires thyroid hormones?

Growth Hormone Releasing Hormone (GHRH)

describe permissive sympathomimetic action

thyroid hormones inc responsiveness to adrenaline and noradrenaline by increasing numbers of receptors

T3 and T4 exert negative feecback on which hormones?

release of TRH and TSH

what kind of receptor is TSH?

G protein coupled receptor

what can alter thyroid hormone levels?

low temp in babies and chlidren stress circadian rhythm

what enzyme is important in the activation and deactivation of thyroid hormone?

Deiodinase enzymes

what does deiodinase enzyme do to thyroid hormone?

adds or removes an iodine atom from the outer ring

what are the two inactive forms of thyroid hormone produced by deioinase enzyme?

**rT3** (reverse T3) from T4 **T2** from T3

of the three subtypes od deiodinase enzyme which is the major determinant in the conversion of T4 to T3?

DII

where are each of the deiodinase enzymes subtypes located?

DI- liver and kidneys DII- heart, skeletal muscle, CNS, thyroid, pituitary DIII- fetal tissue, placenta, brain