Thyroid Flashcards
descirbe primary thyroid disease
disease affecting thyroid gland itself
autoimmune thyroid disease most common
describe scondary thyroid disease
hypothalmic or pituitary disease
no thyroid gland pathology
what is TSH
thyroid stimulating hormone
where is TSH released?
thyrotroph cells in anterior pituitary
TSH is released in response to what?
thyrotropin releasing hormone TRH
TSH is also called what?
thyrotropin
release of TSH results in what?
production of T3 and T4
99% of T4 and T3 is bound to what?
plasma proteins
what plasma proteins do T3 and T4 bind to?
Thyroxine Binding Globulin (TBG)- 70%
Transthyretin (TTR)- 20%
Albumin- 5%
what levels of free T3/4 and TSH would be seeen in primary hypothyroidism
free T3/4 low
TSH high
what levels of T3/4 and TSH would be seen in primary hyperthyroidism?
free T3/4 high
TSH low
what si the difference between primary and secondary thyroid disease?
primary- problem with thyroid gland iself
secondary- problem with hypothalmus/pituitary
what levels of T3/4 and TSH would be seen in secondary hypothyroidism?
low free T3/4
TSH low (or normal)
what levels of free T3/4 and TSH would be seen in secondary hyperthyroidism?
free T3/4 high
TSH high (or normal)
define myxoedema
severe hypothyroidism
pretibial myxoedema is a rare clinical sign in which autoimmune thyroid condition?
Graves disease
graves disease results in hypo/hyperthyroidism?
hyperthyroidism
what are soem goitrous causes of hypothyroidism?
hashimotos thyroiditis
iodine deficiency
what are some non-goitrous causes of hypothyroidism?
atrophic thyroiditis
post radiotherapy
what would be a self-limiting cause of hyperthyroidism?
withdrawl of antithyroid drugs
describe hashimotos thyroiditis?
autoimmune destruction of thyroid gland and reduced thyroid hormone productioin
hashimotos is characterised by which antibodies?
antibodies against thyroid peroxidase (TPO)
what is seen microscopically in hashimotos?
T cell infiltrate
inflammation
what is prescribed to people with hypothyroidism?
levothyroxine
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?
hyperthyroidism
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?
T3
coupling of 2 DIT forms what?
T4
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?
T4
which thyroid hormone is the most biologically active?
T3
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