csv-export (2) Flashcards
what does thyroid hormone synthesis start with? where are they made?
starts with iodination of tyrosine residues on thyroglobulin protein within colloid
synthetic processes occur in follicular cells that line the thryoid follices (epithelium)
how is iodide made into T4/T3?
Na/I? symporter transports idodide into thyroid cells
thryoglobulin + I??> MIT/DIT??> T4/T3
thyroid peroxidase catalyzes the 2 rxns above
which thyroid hormone is predominantly secereted?
which one is the biologically active form?
how are they converted?
thryoxine (T4) is predominantly secreted?? its a prohormone that must be converted into biologically active T3 (tri?iodothyronine)
T3 binds to nuclear receptors of almost all cels in body (modulates gene expression, stimulatory)
T4 is converted to T3 by type 1 deiodinase in liver and type 2 deodinase in order to feedback to pit and hypo
where does T3 act?
brain/CNS maturation
bone growth (GH)
beta=adrengergic/CV effects (inc HR, SV, CO, vasodilation
BMR?? via inc Na/K atpase in most tissues, inc O2 consumption, RR, body tempTSH
TSH
structure? functions?
alpha subunit is same as FSH, LH, HCG
unique beta subunit
fx: growth and vascularity of thyroid
stimulates formation and release of thryoid hormones
iodine uptake, TPO activity, lysosomal activity
STABLE throughout the day
how much free T4 and T3 is there in body?
99% protein bound, 60?70% thryoxine binding globulin
free hormones are the biologically active ones
what are causes of increased and decreased binding proteins?
caused of increased binding proteins:
drugs (estrogen, opiates)
pregnancy
acute hepatitis
cause of decreased binding proteins drugs (androgens, glucocorticoids) malnutrition chronic liver disease/cirrhosis renal disease
inherited: X linked TBG deficiency and mutations TBG
what is significance of testing TSH?
reflects long term (about 6 weeks) of feedback from FT4/FT3 on pituitary
changes in F3/4 cause exponential change in TSH
best test to assess primary thryoid disorders
what thyroid antibodies are tested and what do they show?
3
thyroid peroxidase antibodies (TPOAb) and TSH receptor ABs show pathogenic role in autoimmune thyroid disease, stimulate or block thryoid
changes precede thryoid desfunction
thryoglobulin antiboides: fairly nonspecific
what are 2 thryoid tumor markers?
what are they used for?
thyroglobulin: normal protein in follicular cells of thryoid?? used in surveillance of papillary/follicular thryoid cnacer after treatment
calcitonin
normal protein in C cells of thryoid
used in surveillance of medullary thyroid cancer after tx
NOT USED FOR DIAGNOSIS
which two tests do you do the measure intrinsic activity of thyroid?
radioactive iodine uptake (give iodine orally, percent of uptake at 4 and 24 hours is measured?? measures active transport and organification of iodine)
normal uptake is 15?35%
thyroid scan?? radioiodine or technetium pertechnetate is administered and an IMAGE of isotope uptake is produced
localizes rates of active transport of iodine
hypothyroidism
definition
epidemiology
def: usually primary, caused by thyroid gland dysfunction, failure, absence
more common in women and more common with age?? 15% by age 80!
what are specific causes of hypothyroidism?
loss of thyroid tissue
autoimmune (hashimotos thyroiditis)
post surgical, post?radiation
congenital
dec thyroid hormone production
medications: lithium, amiodarone, interferon
other parts of world: iodine def
hashimotos/chronic lymphocytic thyroiditis
autoimmune destruction of thyroid tissue
usually high titers of anti?thryoid antibodies
lymphocytic infiltration of thyroid gland, fibrosis
you have firm, non?tender diffuse goiter until late stages
what causes the non?pitting edema and periorbital swelling?
accumulation of glycoaminoglycans
