Triiodothyronine

A hormone produced by the thyroid gland

Triiodothyronine (T3) is a thyroid hormone that plays vital roles in the body's metabolic rate, heart and digestive functions, muscle control, brain development, and maintenance of bones. It is one of the two main hormones produced by the thyroid gland, the other being thyroxine (T4).

Structure and Function

Triiodothyronine is a hormone that contains three iodine atoms, hence the name. It is derived from the amino acid tyrosine. T3 is more potent than T4 and is considered the active form of thyroid hormone. It influences almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.

Synthesis

Synthesis of thyroid hormones.

T3 is produced by the thyroid gland and also by the conversion of T4 into T3 in peripheral tissues. This conversion is catalyzed by enzymes called iodothyronine deiodinases.

Mechanism of Action

T3 acts on target tissues by binding to nuclear receptors, which then influence the expression of specific genes. This process regulates various metabolic pathways and is crucial for normal development and metabolism.

Regulation

The production and release of T3 are regulated by the hypothalamic-pituitary-thyroid axis. The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to secrete thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce T3 and T4.

Clinical Significance

Abnormal levels of T3 can lead to various health issues. Hyperthyroidism is characterized by excessive levels of T3, leading to symptoms such as weight loss, increased heart rate, and anxiety. Conversely, hypothyroidism is marked by insufficient T3 levels, causing fatigue, weight gain, and depression.

Related Pages

• Thyroid hormone
• Thyroxine
• Hypothyroidism
• Hyperthyroidism

References

Chemical structure of triiodothyronine.

Iodothyronine deiodinase enzyme.

Diagram of the thyroid system.

Thyroid system overview.