Hypothalamus-Thyroid Axis (HPT)

Question 1

cold temperatures below 37 C or 98.6 F causes the hypothalamus to release ____

Answer 1

Thyrotropin releasing hormone (TRH)

Question 2

Thyrotropin releasing hormone (TRH) stimulates…

Answer 2

anterior pituitary to release thyroid stimulating hormone (TSH)

Question 3

TSH causes…

Answer 3

thyroid to produce
97% T4 (inactive)
3% T3 (active)

Question 4

T4 goes to the ____

Answer 4

liver

Question 5

what happens to T4 in the liver?

Answer 5

bile dependent deiodinase enzyme converts T4 -> T3

Question 6

T4 has a negative feedback on ____

Answer 6

TSH

Question 7

what is the active thyroid hormone?

Answer 7

T3 (3%)

Question 8

Mechanism of action of active thyroid hormone

Answer 8

• 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

Question 9

synthesis of T4 requires the ____ and synthesis of ____

Answer 9

iodine pump
thyroglobulin (TG)
(both turned on by TSH)

Question 10

thyroglobulin consists of many ____

Answer 10

tyrosine molecules

Question 11

Adding iodine to TG requires the enzyme ____ which is ____ dependent

Answer 11

thyroid peroxidase
selenium

Question 12

adding iodine to TG is referred to as ____

Answer 12

organification of iodine

Question 13

T4 & T3 undergo ____ and are released into the blood

Answer 13

receptor mediated endocytosis

Question 14

both T4 & T3 are ____ soluble

Answer 14

lipid

Question 15

increased ____ synthesis would likely be reported in a patient with an iodine deficiency

Answer 15

thyroglobulin

Question 16

affinity for nuclear receptors in target tissues is greater for ____ than ____

Answer 16

T3 > T4

Question 17

inhibition of the iodine pump would be expected to cause…

Answer 17

increased synthesis of TG (stimulated by TSH)

Question 18

Stimulation of the iodine pump would be expected to cause…

Answer 18

Increased synthesis of thyroxine (T4)