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What happens to thyroglobulin when the body needs thyroid hormones?

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Detailed anatomical illustration of the human thyroid gland and surrounding structures, showing the right and left lobes, isthmus, nearby arteries, veins, nerves, lymph nodes, and cartilage in the neck. — thyroid gland Human thyroid gland.

When the body requires thyroid hormones, thyroglobulin—which is stored as the primary component of colloid within the thyroid follicles—is reabsorbed from the follicular lumen into the follicular cells.12

Once inside these cells, the thyroglobulin is hydrolyzed (broken down) by enzymes into its component parts. This process releases the two biologically active thyroid hormones: thyroxine (T4) and triiodothyronine (T3). These hormones then pass out of the cells and into the circulation. Any remaining inactive components, such as iodotyrosines, are processed by enzymes to conserve and recycle iodine for future hormone synthesis.12