Deiodinase T4 to T3 — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

ModeratePhysiology - Endocrine & MetabolicDeiodinase T4 to T3FRCA Primary

Regarding thyroid hormone physiology which enzyme converts T4 to T3 in peripheral tissues?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — 5'-deiodinase (type 1 and type 2)

Type 1 and type 2 5'-deiodinases (also called iodothyronine deiodinases) convert T4 to the more active T3 by removing one iodine atom from the outer ring. Type 3 deiodinase converts T4 to reverse T3 (rT3 / inactive). Propylthiouracil inhibits peripheral conversion of T4 to T3 (in addition to blocking thyroid hormone synthesis).

Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist