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Related Concept Videos

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.
TH is indispensable for the normal development and maturation of the skeletal, muscular, and nervous systems during fetal and childhood growth. It facilitates bone mineral turnover and regulates protein synthesis in developing tissues, contributing significantly to overall growth and...
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...
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...
Hyperthyroidism II: Pathophysiology01:27

Hyperthyroidism II: Pathophysiology

Hyperthyroidism is a hypermetabolic state caused by elevated levels of thyroid hormones, triiodothyronine (T3) and thyroxine (T4). It results from dysregulation at the thyroid, pituitary, or immune system level and affects multiple organ systems.PathophysiologyThe most common cause of hyperthyroidism is Graves’ disease, an autoimmune disorder in which antibodies, specifically thyroid-stimulating antibodies (TSAb), a subtype of TSH receptor antibodies (TRAb), bind to and activate TSH receptors...
Effect of Hepatic Disease on Pharmacokinetics: Pathophysiologic Assessment and Liver Function Test01:22

Effect of Hepatic Disease on Pharmacokinetics: Pathophysiologic Assessment and Liver Function Test

In clinical practice, the direct measurement of hepatic blood flow to evaluate liver function presents significant challenges due to the intricate and specialized nature of the necessary techniques. Consequently, healthcare professionals often rely on empirical estimates derived from thorough patient examinations and liver function tests to gauge liver health. Among the tools at their disposal, the Child–Pugh and MELD scoring systems stand out for their ability to categorize and assess the...
Effect of Hepatic Disease on Pharmacokinetics: Active Drug, Metabolite and Fraction of Metabolized Drug01:14

Effect of Hepatic Disease on Pharmacokinetics: Active Drug, Metabolite and Fraction of Metabolized Drug

In pharmacotherapy, monitoring drug concentrations is paramount, especially for drugs whose therapeutic effects hinge on both the active compound and its metabolite. Hepatic impairment profoundly influences drug potency by altering liver function. If the drug is more potent than its metabolite, impaired liver function amplifies drug activity due to elevated drug concentration levels. Conversely, if the metabolite holds greater potency, diminished liver function diminishes drug activity by...

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Related Experiment Video

Updated: May 26, 2026

A Versatile, Behavioral Method to Investigate Thyroid Hormone Effects on Cerebellar Function
04:05

A Versatile, Behavioral Method to Investigate Thyroid Hormone Effects on Cerebellar Function

Published on: October 6, 2023

Effect of phenytoin therapy on thyroid function.

J F Finucane1, R S Griffiths

  • 1Department of Medicine, Queen Elizabeth Hospital, Birmingham B15 2TH.

British Journal of Clinical Pharmacology
|January 6, 2012
PubMed
Summary
This summary is machine-generated.

Phenytoin medication can alter thyroid hormone levels by displacing thyroxine and triiodothyronine from binding proteins. This leads to increased free thyroxine but maintains euthyroid status and increases urinary thyroxine loss.

Related Experiment Videos

Last Updated: May 26, 2026

A Versatile, Behavioral Method to Investigate Thyroid Hormone Effects on Cerebellar Function
04:05

A Versatile, Behavioral Method to Investigate Thyroid Hormone Effects on Cerebellar Function

Published on: October 6, 2023

Area of Science:

  • Endocrinology
  • Pharmacology

Background:

  • Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are crucial for metabolic regulation.
  • Phenytoin is an anticonvulsant medication with known interactions with various physiological systems.

Purpose of the Study:

  • To investigate the effects of long-term therapeutic phenytoin doses on serum thyroid hormone levels (total and free T4 and T3).
  • To assess urinary excretion of unconjugated thyroid hormones in phenytoin-treated individuals.
  • To elucidate the mechanism by which phenytoin influences thyroid hormone homeostasis.

Main Methods:

  • Measurement of serum total and free thyroxine and triiodothyronine concentrations.
  • Quantification of urinary losses of unconjugated thyroxine and triiodothyronine.
  • Comparison between normal subjects and patients on long-term therapeutic phenytoin doses.

Main Results:

  • Phenytoin treatment resulted in decreased total serum T4 and T3 concentrations.
  • Increased free fractions of T4 and T3 were observed, with a significant rise in free T4 but not free T3.
  • Urinary excretion of unconjugated thyroxine increased, while unconjugated triiodothyronine excretion remained normal.
  • Despite alterations, serum free hormone concentrations stayed within the euthyroid range.

Conclusions:

  • Therapeutic doses of phenytoin displace thyroxine and, to a lesser extent, triiodothyronine from serum binding proteins.
  • This displacement leads to increased peripheral clearance of thyroid hormones.
  • Phenytoin's effects on thyroid hormone binding proteins do not typically result in clinical hypothyroidism.