Hypothalamus-Thyroid Axis (HPT) Flashcards
cold temperatures below 37 C or 98.6 F causes the hypothalamus to release ____
Thyrotropin releasing hormone (TRH)
Thyrotropin releasing hormone (TRH) stimulates…
anterior pituitary to release thyroid stimulating hormone (TSH)
TSH causes…
thyroid to produce
97% T4 (inactive)
3% T3 (active)
T4 goes to the ____
liver
what happens to T4 in the liver?
bile dependent deiodinase enzyme converts T4 -> T3
T4 has a negative feedback on ____
TSH
what is the active thyroid hormone?
T3 (3%)
Mechanism of action of active thyroid hormone
- T3 (fat soluble) has nuclear receptor which increases gene transcription -> increases number & size of mitochondria
- increases BMR and temperature (metabolism) -> negative feedback on hypothalamus, turns off TRH
synthesis of T4 requires the ____ and synthesis of ____
iodine pump
thyroglobulin (TG)
(both turned on by TSH)
thyroglobulin consists of many ____
tyrosine molecules
Adding iodine to TG requires the enzyme ____ which is ____ dependent
thyroid peroxidase
selenium
adding iodine to TG is referred to as ____
organification of iodine
T4 & T3 undergo ____ and are released into the blood
receptor mediated endocytosis
both T4 & T3 are ____ soluble
lipid
increased ____ synthesis would likely be reported in a patient with an iodine deficiency
thyroglobulin
affinity for nuclear receptors in target tissues is greater for ____ than ____
T3 > T4
inhibition of the iodine pump would be expected to cause…
increased synthesis of TG (stimulated by TSH)
Stimulation of the iodine pump would be expected to cause…
Increased synthesis of thyroxine (T4)
