Hypothalamus, anterior pituitary and thyroid
Thyroid axis (HPT)
The body's thermostat and idle-speed dial.
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Net yieldTRH and cold in, T₃/T₄ out: basal metabolic rate set
Steps3
The three tiers
TRH → TSH → T₃/T₄: hypothalamus, pituitary, thyroid
Reading the labs
Low T₄ with high TSH: thyroid's fault. Low T₄ with low TSH: look upstream.