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
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