ypothalamus-pituitary-thyroid axis TRH: thyrotropin-releasing hormone TRH TSH thyroid-stimulating hormone TSH Pituitary TSH receptor T4: thyroxine Th id GG protein homone T3: triiodothyronine T3, T receptor GTP G void Target The net effect of t4 t3 tcAMP on t basal metabolic rate (BMR) Gene expression onhypothalamus-pituitary-thyroid axis The net effect of T4 T3 :  basal metabolic rate (BMR) TRH: thyrotropin-releasing hormone TSH: thyroid-stimulating hormone T4: thyroxine T3: triiodothyronine