Thyroid Flashcards
what do colloid cells contain?
tyrosine and thyroglobulin
what do parafollicular C cells secrete?
calcitonin
explain the synthesis and storage of T3 and T4
- iodine is taken up by the follicle cells,
- iodine attached to tyrosine residues on thyroglobulin to form MIT + DIT.
- Coupling of MIT + DIT = T3 and 2(DIT) = t4
- stored in colloid
is t4 more potent than t3?
no t3 is 4 times more potent than t4
where in the body can t4 be converted to t3?
in the liver and kidney
what form of thyroid hormone is active? bound or unbound
unbound
what is the most abundant plasma protein that thyroxine attaches to?
thyroxine binding globulin (70%)
what is the purpose of thyrotrophin (TRH)
comes from the hypothalamus, stimulates TSH from anterior pituitary
embryologically where does the thyroid develop from?
invagination of the pharyngeal epithelium, descends from foramen caecum to normal location along the thyroglossal duct
what are the embryological abnormalities of thyroid?
failure to descend = lingual thyroid,
excessive descent = retrosternal location and thryoglossal duct cyst
biochemically what is happening in hyperthyroidism?
excess T3 and T4
85% of hyperthyroidism are due to?
Graves disease
what antibodies are seen in Graves disease?
TSH receptor antibodies
what are the triad of features in Graves disease?
hyperthyroid, exophthalmos and pretibial myxodema
what is the most common cause of hypothyroid?
Hashimoto’s
what age range is Hashimotos?
45-60
polymorphisms in what genes predispose to Hashimotos?
CTLA-4 and PTPN-22
what are the 4 types of thyroid cancer?
papillary, follicular, medullary and anaplastic
what is the most common form of thyroid cancer?
papillary carcinoma
what is the second most common thyroid cancer?
follicular carcinoma
Describe the thyroid cytology system
Thy1 = uninterpretable Thy2 = benign Thy3 = atypical, probably benign thy4= atypical probably malignant thy5 = malignant
what are the two subtypes of goitre?
diffuse or nodular
what are the causes of goitre
iodine deficiency, multi nodular, graves, thyroiditis, tumour, cysts, inherited
what would make you think a thyroid nodule was malignant?
below 20 or over 70, male sex, dysphagia/dysphonia, firm hard or immobile lump, lymphadenopathy
what is thyroid acropachy?
soft tissue swelling and periostial bone changes
what is the thyroid cytology cut off for surgery?
THY3 and above
FSH is greater than 30 on two separate occasions what does this indicate?
Peri/menopausal
normal thyroid appearance on imaging?
low level uptake, symmetrical
Graves disease on imaging?
diffuse uptake, symmetrical
Multi nodular goitre on imaging?
asymmetrical, patches of intense uptake and patches missed
describe primary hyperthyroidism (biochemically)
TSH is LOW, T3/4 HIGH, overactive thyroid
describe primary hypothyroid (biochemically)
TSH is HIGH, t4/3 LOW, failing thyroid
why should hypothyroid be restored gradually?
can cause arryhthmias
treatment of hypothyroid in younger patients?
50-100 ug/day
treatment of hypothyroid in the elderly?
25-50ug.day adjusted every 4 weeks
what is the treatment of Hyperthryoidism?
Carbimazole or Propylthiouracil
when should TSH be checked after thyroxine therapy begins?
2 months after any dose change, when stable 12-18 months
what should the dose of thyroxine be increased by in pregnancy?
25ug
what age range is De Quervains?
females 20-50 years
describe the changes in T4 in De quervains
High in early stage, low in late and then returns to normal
describe the changes in TSH in De Quervains
low in early stage, high in late, then normal
