Thyroid Physiology Flashcards
The thyroid is supplied by the
superior and inferior thyroid artery and vein
__ is the biologically active thyroid hormone
T3
__ doesn’t play a physiologic role but is a tumor marker for ___ thyroid cancer
Calcitonin; medullary
Thyroid increases basal ____ rate in all tissues except
metabolic; brain, testes, spleen
Thyroid effect on CV system
increases expression of alpha myosin heavy chains, which increases contractility and heart rate
Thyroid effect on heme
increases oxygen dissociation
Congenital hypothyroidism symptoms (aka cretinism)
severe mental retardation and dwarfism
T4 and T3 are made where
T4 exclusively in the thyroid gland, 80% of T3 converted from T4 outside the thyroid
_ has the major regulatory feedback on the hypothalamus and pituitary
T3
__ is required to synthesize thyroid hormone
iodine
This group needs more iodine and this other group need the most iodine
pregnant women, breast feeding women
Thyroglobulin is made by what and stored by
thyroid follicular epithelial cells; colloid
What is penderin
a iodine/cl transporter which move iodine to the membrane-colloid interface
Two reactions TPO catalyzes
Oxidation of Iodide to iodine and iodination of the thyroid hormone (adding iodine to it)
TPO gene stimulated by
TSH
Why do you have more T4 in the thyroid
it’s made 10x faster than T3
T4, T3 and uncoupled DIT/MIT are bound to what in the colloid
Thyroglobulin
MIT and DIT combination is catalyzed by
TPO
What happens when the thyroid gland is stimulated by TSH
colloid is taken to the follicular cells by pinocytosis and there the thyroglobulin is cleaved off T3/T4 by proteases
Iodines are cleaved from unused DIT and MIT
by an enzyme called
thyroid deiodinase
Reverse T3 is ____ (activity)and made from ___
inactive; T4 iodine cleaved off the inner ring
Over 70% of T4/T3 are abound to
TBG
Half lives of T4/T3 and its significance
T4- 8 days, T3- one day, T4 is biologically very available
Estrogen and Hepatitis do what to TBG
increase it
How does pregnancy affect free T3 levels
doesn’t affect em, achieves steady state
__ is the best measurement for thyroid function
TSH
Thyroid remains connected to foramen cecum by the __, which regresses at 8 weeks
thyroglossal duct
