Hypothalamus-Pituitary-Thyroid Axis.
Level 5 - mechanism / opinion, no new human data
Narrative physiological review describing biological mechanisms without original empirical human data.
PubMed 27347897 · doi:10.1002/cphy.c150027
What was done
This paper is a comprehensive narrative review outlining the physiological regulation and molecular mechanisms of the hypothalamus-pituitary-thyroid (HPT) axis, thyroid hormone biosynthesis, negative feedback loops, and peripheral tissue action.
What was found
The abstract reports no experimental trial data, stating only that circulating serum concentrations of thyroxine (T4) are roughly 100-fold higher than triiodothyronine (T3). It details the biological pathway wherein hypothalamic TRH stimulates pituitary TSH to induce thyroidal T4 and T3 release. At target tissues, T4 undergoes enzymatic activation to T3 via 5'-deiodinases (D1 and D2) or inactivation to reverse T3 via 5-deiodinase (D3).
Why it matters
It provides a consolidated foundational reference on endocrine feedback loops and enzymatic pathways controlling thyroid hormone homeostasis and cellular metabolic regulation.
Limits
As a narrative review, it presents mechanistic syntheses without systematic search criteria, meta-analytic pooling, or original empirical data.
Cited by
- context Reverse T3 is produced by the body and acts as a physiological brake when active T3 levels are elevated.