Thyrotroph — thyroid-stimulating hormone
Pituitary · TSH Shared alpha subunit Gs to cAMP
A glycoprotein sharing its alpha subunit with LH, FSH and hCG, its beta subunit giving specificity. It binds a Gs-coupled receptor on the follicular cell and drives every step from iodide uptake to hormone release, plus follicular growth.
Traced from the start
- Thyrotrophin-releasing hormone (paraventricular nucleus)
- Thyrotroph — thyroid-stimulating hormone
Detail
- Relationship
- TSH varies log-linearly with free T4, so a small fall in T4 gives a large TSH rise — the most sensitive test of primary thyroid function and useless alone in pituitary disease
- Cross-reaction
- hCG weakly stimulates the TSH receptor: transient gestational thyrotoxicosis with hyperemesis, and overt disease in molar pregnancy
- Suppressed by
- T4 and T3, dopamine, glucocorticoids, somatostatin and severe non-thyroidal illness
When it goes wrong
Pituitary or hypothalamic damage (secondary hypothyroidism)
Low free T4 with a low or inappropriately normal TSH; TSH cannot titrate replacement, so dose against free T4 in the upper half of the range
TSH-secreting adenoma or thyroid hormone resistance
Raised free T4 and T3 with an unsuppressed TSH — the pattern that must not be treated as primary thyrotoxicosis
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