Thyroid follicular cell
Target gland or tissue · NIS TPO Thyroglobulin
TSH drives iodide trapping by the sodium-iodide symporter, then thyroid peroxidase oxidises and organifies iodide onto thyroglobulin tyrosines and couples them; colloid is endocytosed and hydrolysed to release T4 and T3.
Traced from the start
Detail
- Output
- About 100 microgram of T4 but only 5-10 microgram of T3 a day — the gland is a T4 factory and most T3 is made peripherally
- Autoregulation
- A large iodide load transiently blocks organification (Wolff-Chaikoff); in a nodular gland the same load can precipitate thyrotoxicosis (Jod-Basedow)
- Drugs
- Carbimazole and propylthiouracil block thyroid peroxidase; PTU also blocks peripheral T4 to T3 conversion, so it is preferred in thyroid storm and the first trimester
- Uptake pathway
- Radioiodine and pertechnetate enter through the same symporter, which is what an uptake scan measures
When it goes wrong
TSH-receptor stimulating antibody (Graves disease)
Thyrotoxicosis with diffuse goitre and suppressed TSH; the receptor is driven regardless of feedback, and the antibody crosses the placenta to cause neonatal thyrotoxicosis
Amiodarone or iodinated contrast
Type 1 thyrotoxicosis from excess substrate in a nodular gland, or type 2 destructive thyroiditis, which is treated with glucocorticoids rather than thionamides
Practise this structure
4 questions in the bank tagged Thyroid.
A 42-year-old man was treated with radioactive iodine for Graves disease three days ago. He now reports dry mouth and painful swelling in front of both ears, wo…
Clinical rotations · common
A 34-year-old woman taking carbimazole for Graves disease presents with fever, malaise and two painful oral ulcers. She has a temperature of 38.7°C and mild cer…
Clinical rotations · common
A 35-year-old woman has palpitations and a 9 kg weight loss over 3 months. Her free thyroxine is 48 pmol/L (reference 10–22 pmol/L), TSH is less than 0.01 mIU/L…
Mechanisms of disease · common
A 38-year-old woman presents with two weeks of pain in the front of her neck radiating to her jaw, together with palpitations, sweating and 2 kg of weight loss.…
Clinical rotations · common