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Terms in this set (17)
TRH from the hypothalamus stimulates production of ___________ from the anterior pituitary, which acts on the thyroid to produce ______ and ______.
TSH; T3 and T4 (more T4, but T3 is more biologically active)
What are the 6 effects of thyroid hormones T3 and T4?
1. increased Na+-K+ ATPase synthesis
2. increased metabolism
3. increased cardiac output
4. increased bone formation and growth
5. CNS maturation
6. interactions with SNS (not important)
T3 and T4 provide negative feedback on ________ and ________.
TSH and TRH
What three things stimulate TH release?
1. stress (cold)
2. TBG levels (thyroid binding globulins; increase during pregnancy)
3. thyroid stimulating IgGs
What 7 things inhibit TH release?
4. iodine deficiency
5. excess iodine intake
6. decreased TBG levels
7. pharmacological agents (Na+/I- cotransporter inhibitors, peroxidase inhibitors)
What is the only difference between T3 and T4?
T3 has 3 iodines bound, T4 has 4
What substance is stored within the lumen of the follicular epithelial cells of the thyroid?
What is the role of thyroid peroxidase in thyroid hormone synthesis?
it adds I2s and tyrosines to thyroglobulins; it also converts I- to I2 (iodine)
end product is one T3 and one T4 attached to the same thyroglobulin
When stimulated, _________ within follicular cells of the thyroid dissociate thyroglobulin from T3 and T4, which are then released into the bloodstream. Here they are bound by ___________ ________ ____________ until they reach their target cells.
proteases; thyroid-binding globulins
TSH from the anterior pituitary increases what five things?
1. activity of the Na+/I- cotransporter
2. thyroglobulin synthesis
3. iodination and conjugation
5. T3 and T4 secretion
The thyroid hormone ________ can be converted into _________ in target tissues, especially in the liver and kidney by the enzyme __________ type 1.
T4; T3; deiodinase
Is all circulating thyroid hormone bound to thyroid-binding globulins? Is it active when it is bound?
no, but most of it is bound; no
Why are there higher levels of TBGs during pregnancy? What does this lead to?
because estrogen causes a decrease in the hepatic breakdown of TBG
less negative feedback on TSH and TRH causes an increase in TSH, T4, and T3 (bound and free)
What is the net effect of increased circulating levels of TBGs during pregnancy? (transiently and sustained)
transient effects: increased bound T3 and T4, but decreased free T3 and T4
sustained effects: increased bound and normal free T3 and T4
Is iodine important during pregnancy?
yes; women should drastically increase their iodine intake as it it essential to fetal development
What is cretinism? What can it lead to? Is it reversible?
congenital hypothyroidism; growth and mental retardation; reversible if treated
What can cause an enlarged thyroid?
hyper- and hypothyroidism
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