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Synthesis and Regulation of Thyroid Hormones

Synthesis and Regulation of Thyroid Hormones

Low blood levels of the thyroid hormones — triiodothyronine (T3) and thyroxine (T4) — signal the hypothalamus to release the thyrotropin-releasing hormone (TRH). TRH then reaches the pituitary gland and stimulates the release of thyroid-stimulating hormone(TSH) into the bloodstream.
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The thyroid hormone (TH) plays a pivotal role in the intricate orchestration of physiological processes, exerting profound effects on development, metabolism, and homeostasis throughout different life stages.
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Hypothyroidism is a disorder characterized by insufficient production of thyroid hormones, which regulate metabolism, energy balance, and multiple organ systems.TypesHypothyroidism is classified based on the level of dysfunction. Primary hypothyroidism results from intrinsic thyroid gland dysfunction, causing reduced hormone production despite normal or increased stimulation. Secondary hypothyroidism arises from inadequate thyroid-stimulating hormone (TSH) secretion by the pituitary. Tertiary...

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Related Experiment Video

Updated: May 11, 2026

An Ex vivo Culture System to Study Thyroid Development

An Ex vivo Culture System to Study Thyroid Development

Published on: June 6, 2014

Maternal thyroid function at gestational weeks 11-13 in twin pregnancies.

Ghalia Ashoor¹, Ornella Muto, Leona C Y Poon

¹1 Harris Birthright Research Center for Fetal Medicine, King's College Hospital , London, United Kingdom .

Thyroid : Official Journal of the American Thyroid Association

|May 11, 2013

Summary

Thyroid-stimulating hormone (TSH) is lower in twin pregnancies compared to singletons, while free thyroxine (FT4) levels remain similar. These findings aid in diagnosing thyroid function in twin pregnancies.

Related Experiment Videos

Last Updated: May 11, 2026

An Ex vivo Culture System to Study Thyroid Development

An Ex vivo Culture System to Study Thyroid Development

Published on: June 6, 2014

Area of Science:

Endocrinology
Maternal-Fetal Medicine
Reproductive Biology

Background:

Thyroid disease in pregnancy poses risks for complications.
Human chorionic gonadotrophin (hCG) in early pregnancy suppresses serum thyrotropin (TSH).
Higher hCG in twin pregnancies may cause more pronounced TSH suppression.

Purpose of the Study:

Establish reference ranges for maternal serum TSH and FT4 at 11-13 weeks gestation in twin pregnancies.
Differentiate physiologic TSH suppression from overt thyroid disease in twin gestations.
Provide a basis for studying thyroid function in pathological pregnancies.

Main Methods:

Case series of 177 dichorionic and 58 monochorionic twin pregnancies with normal outcomes.
Inclusion of 19 monochorionic pregnancies with twin-twin transfusion syndrome.
Measurement of maternal serum TSH, FT4, and antibodies at 11-13 weeks gestation.
Conversion of TSH and FT4 to multiples of median (MoM) relative to singleton pregnancies.

Main Results:

Antibody-negative twin pregnancies showed lower TSH MoM (0.62) compared to singletons (1.01).
FT4 MoM was not significantly different between twin and singleton pregnancies.
Free beta-hCG MoM was higher in twin pregnancies (1.91) versus singletons (0.98).
No significant differences in TSH, FT4, or free beta-hCG MoM were observed in twin-twin transfusion syndrome pregnancies compared to normal twins.

Conclusions:

Maternal serum TSH is lower in twin pregnancies compared to singletons.
Maternal serum FT4 levels are comparable between twin and singleton pregnancies.
Established reference ranges are crucial for diagnosing thyroid dysfunction in twin pregnancies.