Thyroid Pt 1 Flashcards
the thyroid gland is innervated why what nerves?
sympathetic
what are the functional units of the thyroid gland?
thyroid follicles
describe the structure of thyroid follicles
single layer of epithelial cells surrounding a lumen that contains colloid
what kinds of follicles are in the thyroid gland?
thyroid follicles, parafollicular cells
parafollicular cells are a source of…
calcitonin
what is the function of the thyroid gland?
secrete the quantity of thyroid hormone to meet the demand of peripheral tissues
what regulates the release of thyroid hormones? how?
blood flow; affects delivery of TSH, iodine and nutrients
what controls the blood flow through the thyroid gland?
postganglionic sympathetic nerves
what are the biologically active forms of thyroid hormone?
T4 and T3
what are the inactive form of thyroid hormone? where does it get made?
rT3 and T2; formed in peripheral tissues
where is TSH made?
anterior pituitary
which benzene ring is numbered with a prime?
distal benzene ring
what proteins are necessary for the synthesis of T4 and T3?
transporter: NIS
thyroglobuline: TG
thyroid peroxidase: TPO
where does most of our iodine intake occur in North America?
iodized salt
what does NIS do?
brings in iodine against its concentration gradient while also bringing in Na. This is possible due to maintenance of the Na gradient by Na/KATPase
significance of perchlorate?
blocker of iodine; can be used to treat hyperthyroidism
describe the significance of radioactive iodine
- bad/poses danger if you’re exposed to radiation
- can be used to treat cancer
describe relationship of other halogens with iodine
anions can compete with iodine with transport (just trying to balance charge); so when their concentration is high, this can inhibit iodine uptake and lead to hypothyroidism
when is thyroshield recommended?
when there’s a radioactive accident; it brings in a lot of iodine that the thyroid gland can use as competition with the radioactive isotope
true or false: the thyroid gland will show preference to uptaking the iodine it needs over an isotope
false
which enzyme is responsible for the iodination of Tg?
TPO - thyroperoxidase
which enzyme makes H2O2 necessary for the organification of TG?
dual-oxidase
what aspect of the thyroid gland is often targeted in drug treatment?
regulation of TPO
numbering of t3?
3, 5, 3’
what is sick euthyroid syndrome?
when there’s more r-T3 (inactive) than T3 (active)
similar to hypothyroidism
most r-T3 is produced where?
peripheral tissues (product of metabolism in general)
true or false: T3 and T4 require a binding protein
true, they are lipophilic
what would be the side effect of a drug that competes for the binding proteins of T3 and T4? (e.g. anti-epileptic drugs)
effect similar to hyperthyroidism because there would be more free T3 and T4
what are the binding proteins of T3 and T4 called?
- thyroxine binding globulin (TBG)
- Transthyretin, aka thyroxine binding prealbumin TBPA
- Albumin
do thyroid epithelial cells produce more of T3 or T4?
T4 - more concentrated but less active
which is more biologically active? T3 or T4?
T3
why is T4 more concentrated than T3?
it’s better at binding to binding proteins
true or false: only bound T3 and T4 are biologically active
false: only free ones are active
in what scenarios would more binding proteins be produced?
pregnancy, use of oral contraceptives
in what scenarios would fewer binding proteins be produced?
starvation, liver disease
the more binding protein, the (more/less) total hormone required to maintain free hormone level
more
Tg is produced where? Thyroxine binding globulin is produced where?
Tg: thyroid’s follicular cells
binding proteins: liver
which deiodinase converts T4 to rT3?
type III
what’s unique about deiodinases?
they contain the 21st amino acid (selenocysteine)
what regulates local modulation of thyroid hormone?
deiodinases
what would it mean for cells if they down-regulated their production of deiodinases?
in the event that there’s less free and active T3 and T4, they can reduce the amount of deiodinases to better use what’s available
