How does thyrotropin stimulate the thyroid gland?

Thyrotropin, also known as thyroid-stimulating hormone (TSH), stimulates the thyroid gland by binding to specific receptors on the surface of thyroid follicular cells. This binding initiates several physiological responses:12

• Hormone Secretion: It triggers the breakdown of thyroglobulin, a storage protein, which leads to the release of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) into the circulation.12
• Biosynthesis: It stimulates the synthesis of additional thyroglobulin and thyroid hormones, as well as the enzymes required for their production.13
• Cellular Activity: Thyrotropin may exert its effects by stimulating the synthesis of cyclic AMP (cAMP) within the cells. It increases the rates of glucose metabolism and protein synthesis, and promotes the resorption of thyroid colloid.2
• Growth: Prolonged stimulation by thyrotropin leads to increased iodide uptake and the growth of thyroid cells, which can result in the enlargement of the gland, known as a goitre.12