THYROID-PHYSIOLOGY

SUMMARY

1. TRH in the hypothalamus stimulates the pituitary to secrete TSH, which then stimulates secretion of thyroxine (T₄) by the thyroid.

2. Triiodothyronine (T₃) is the active hormone; 80% is produced by deiodination of T₄ in the peripheral tissues, 20% secreted by the gland.

3. T₄ & T₃ bind to TBG and albumin.

4. Only a very small fraction of the total T₄ and total T₃ is unbound, free & active. These are the components that are measured.

Reference(s)

Wilkinson, I., Furmedge, D. and Sinharay, R. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press. Get it on Amazon.
Feather, A., Randall, D. and Waterhouse, M. (2020). Kumar And Clark’s Clinical Medicine. 10th ed. S.L.: Elsevier Health Sciences. Get it on Amazon.
Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
Therapeutic Guidelines. Melbourne: Therapeutic Guidelines Limited. https://www.tg.org.au [Accessed 2021].