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
5 questions in the bank tagged Thyroid.
A 38-year-old woman presents with three weeks of aching pain in the front of her neck that worsens when she turns her head or swallows and radiates up to both e…
Clinical rotations · middle twist
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