Thyroid

Question 1

How does thyroid peroxidase function?

Answer 1

Binds I- and TG at apical membrane at separate sites.

Oxidises I- and transfers to Tyr residue on TG

Most efficient at beginning of reaction.

Question 2

What are the main actions of thyroid hormones.

Answer 2

Growth (bone elongation, axonal)

Metabolic rate (plasma Na/K , enzymes, oxidative phosphorylation, )

Nervous system excitability.

Question 3

How is thermogenesis regulated by thyroid hormones?

Answer 3

Increase UCP

Sympathetic output to brown fat (thermogenesis) 
Skeletal muscle (gluconeogenesis).

Question 4

What are the deiodinases?

Answer 4

D1 –> 40% converts T4 to T3

D3 –> 45% converts T4 to rT3 (inactive form limiting exposure to active form)

D2 –> brain isoform - T3 for negative feedback.

Question 5

How are thyroid hormones involved in seasonal changes in body mass?

Answer 5

Short days –> reduced body weight in winter
Absence of restricted food availability doesn’t change this.

T3 supplement reverses effect.

Question 6

What is the most common form of hyperthyroidism?

Answer 6

Graves’ disease

Question 7

What is notable about hyperthyroidism?

Answer 7

10 X more prevalent in women