Bio L2 Thyroid Hormones

Question 1

What molecule inhibits iodide uptake in thyroid?

Answer 1

Thiocyanate

Question 2

What enzyme coverts iodide to iodine?

Answer 2

Thyroid peroxidase (TPO)

Question 3

What is organification reaction?

Answer 3

Iodination of tyrosine residues (at position 3 first)

Question 4

What releases when 2 DIT couple

Answer 4

Thyroxine and alanine

Question 5

TPO is inhibited by?

Answer 5

Methimazole & PTU

Question 6

What are PD and MCT

Answer 6

PD: pendrin (transports iodide to colloid cavity)
MCT: mono carboxyl transporter (transports hormones into blood)

Question 7

T4:T3 ratio? Which is more efficient?

Answer 7

30:1 , T3

Question 8

What are the carriers ?

Answer 8

Albumin, thyroxine-binding globulin (alpha), prealbumin (only T4)

Question 9

Which form affects regulation?

Answer 9

Free form, negative feedback inhibits TSH

Question 10

What effect does T3 have on cells?

Answer 10

T3 receptors are in the nucleus, they stimulate metabolic activities (production of proteins)
Increases Na/K ATPase —> more ATP needed

Question 11

Effects on CHO metabolism

Answer 11

Liver glycogenolysis, intestinal glucose absorption, potentiate epinephrine glycogenolysis effect

Question 12

Effect on fat

Answer 12

Stimulates hormone sensitive lipase in fats, stimulates FA oxidation, reduces cholesterol as it promotes its oxidation to bile acids

Question 13

Regulation of thyroid hormones

Answer 13

1) Hypothalamic-hypophyseal-thyroid axis
2) Auto-regulation by iodide content (low=increase sensitivity to TSH & higher T3 than T4)
3) Peripherally by hormone conversion to inactive rT3