Thyroid Hormones: Functions, Mechanism, and Regulation

Study Notes

Thyroid Hormones

Overview

Thyroid hormones are produced by the thyroid gland, a butterfly-shaped gland located in the neck
They play a crucial role in regulating metabolism, growth, and development

Types of Thyroid Hormones

Triiodothyronine (T3): the most active form of thyroid hormone, responsible for regulating metabolism and energy production
Thyroxine (T4): the less active form of thyroid hormone, converted to T3 in the liver and other tissues
Reverse T3 (rT3): an inactive form of thyroid hormone, produced in small amounts

Functions of Thyroid Hormones

Regulate metabolic rate and energy production
Influence growth and development, particularly in children and adolescents
Regulate body temperature
Affect heart rate and cardiac output
Involved in the regulation of muscle strength and tone

Mechanism of Action

Thyroid hormones bind to specific receptors in the nucleus of target cells
This binding activates gene transcription, leading to changes in protein synthesis and cellular metabolism
Thyroid hormones also have non-genomic effects, influencing cellular signaling pathways and ion channels

Regulation of Thyroid Hormones

Thyroid-stimulating hormone (TSH) from the pituitary gland stimulates the thyroid gland to produce thyroid hormones
Thyroid hormones, in turn, feedback to inhibit TSH production
The hypothalamic-pituitary-thyroid (HPT) axis regulates thyroid hormone production and balance

Clinical Significance

Hypothyroidism: a condition characterized by low thyroid hormone levels, resulting in fatigue, weight gain, and dry skin
Hyperthyroidism: a condition characterized by high thyroid hormone levels, resulting in weight loss, anxiety, and rapid heart rate
Thyroid hormone replacement therapy is used to treat hypothyroidism and thyroid cancer

Description

Learn about the different types of thyroid hormones, their functions, mechanism of action, and regulation. Understand the clinical significance of thyroid hormones and how they affect the body. Test your knowledge on thyroid hormones and their role in metabolism, growth, and development.