Thyroid hormones : Overview

The thyroid gland is a butterfly-shaped endocrine organ located in the anterior neck, just below the Adam's apple. It plays a crucial role in regulating various physiological processes through the production and secretion of thyroid hormones. The primary hormones produced by the thyroid gland are thyroxine (T4) and triiodothyronine (T3).

Thyroxine (T4) is the predominant hormone released by the thyroid gland, accounting for about 90% of the hormone output. Despite its abundance, T4 is relatively inactive and serves mainly as a precursor to T3.

Triiodothyronine (T3), although produced in smaller quantities, is the biologically active form of thyroid hormone and is responsible for regulating metabolism, growth, and development. Most T3 is derived from the peripheral conversion of T4 through deiodination.

Additionally, the thyroid gland produces reverse T3 (rT3), an inactive form that serves as a marker for certain pathological conditions such as the sick euthyroid syndrome.

The hormones are transported in the bloodstream predominantly bound to proteins such as thyroxine-binding globulin (TBG), transthyretin, and albumin, ensuring their availability to various tissues in the body where they exert their metabolic effects.