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Related Concept Videos

Synthesis and Regulation of Thyroid Hormones01:20

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.
Upon reaching the thyroid gland, TSH stimulates the follicular cells' active uptake of iodide ions from the blood. The ions diffuse to the apical surface of the cells and are oxidized to iodine. The iodine is then...
Functions of Thyroid Hormones01:18

Functions of Thyroid Hormones

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 II: Pathophysiology01:23

Hypothyroidism II: Pathophysiology

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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Hyperthyroidism I: Introduction

Hyperthyroidism is a type of thyrotoxicosis characterized by the thyroid gland's overproduction of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). This hormone excess increases the basal metabolic rate and enhances sensitivity to catecholamines.DiagnosisDiagnosis is based on clinical features and biochemical testing. It typically shows suppressed thyroid-stimulating hormone (TSH) levels below 0.4 mIU/L, with elevated free T3 and/or T4. Additional tests, including thyroid...
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Thermoregulation

The human body has a sophisticated thermoregulation system that employs negative feedback mechanisms to maintain an optimal core temperature. When the core temperature drops, peripheral and central thermoreceptors send signals to the hypothalamus, activating the heat-promoting center. This center triggers several responses aimed at increasing the core temperature. First, vasoconstriction reduces the flow of warm blood from internal organs to the skin so that the heat is not lost from the skin,...
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Related Experiment Video

Updated: Jul 4, 2026

Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans
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Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans

Published on: June 2, 2023

Caloric restriction but not exercise-induced reductions in fat mass decrease plasma triiodothyronine concentrations:

Edward P Weiss1, Dennis T Villareal, Susan B Racette

  • 1Division of Geriatrics and Nutritional Sciences, Department of Internal Medicine, Washington University School of Medicine, St Louis, MO, USA. eweiss4@slu.edu

Rejuvenation Research
|July 3, 2008
PubMed
Summary
This summary is machine-generated.

Caloric restriction (CR) significantly lowers triiodothyronine (T3) levels in middle-aged adults. This T3 reduction is linked to CR itself, not just fat loss from exercise.

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Infrared Thermography for the Detection of Changes in Brown Adipose Tissue Activity
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Infrared Thermography for the Detection of Changes in Brown Adipose Tissue Activity

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Last Updated: Jul 4, 2026

Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans
04:54

Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans

Published on: June 2, 2023

Infrared Thermography for the Detection of Changes in Brown Adipose Tissue Activity
08:16

Infrared Thermography for the Detection of Changes in Brown Adipose Tissue Activity

Published on: September 28, 2022

Area of Science:

  • Endocrinology
  • Metabolic Health
  • Nutrition Science

Background:

  • Caloric restriction (CR) is known to decrease circulating triiodothyronine (T3) levels.
  • It remains unclear whether this effect is a direct consequence of CR or secondary to CR-induced reductions in body fat mass.

Purpose of the Study:

  • To investigate whether plasma T3 concentration decreases with CR-induced fat mass reduction.
  • To determine if similar fat mass reductions achieved through exercise elicit the same effect on T3 levels.

Main Methods:

  • A 12-month randomized controlled trial involving sedentary, nonobese middle-aged men and women.
  • Participants were assigned to either caloric restriction (n=18), exercise-induced weight loss (n=17), or a control group (n=9).
  • Measurements included body composition and plasma concentrations of thyroid hormones (T3, TSH, T4, FT4) at baseline and 12 months.

Main Results:

  • Both CR and exercise groups achieved significant reductions in fat mass, with no significant difference between the groups.
  • Plasma T3 concentration significantly decreased in the CR group (p < 0.0001) but not in the exercise group (p = 0.07) or control group (p = 0.65).
  • Thyrotropin (TSH), thyroxine (T4), and free thyroxine (FT4) levels remained unchanged across all groups.

Conclusions:

  • Twelve months of CR leads to a significant decrease in circulating T3 concentrations in middle-aged adults.
  • The observed reduction in T3 is likely attributable to CR itself, rather than solely to the associated decrease in body fat mass, as exercise-induced fat loss did not produce a comparable effect.