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How is thyroglobulin moved from the colloid into thyroid follicular cells?

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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 thyroid hormones are required, thyroglobulin is reabsorbed from the colloid stored in the follicular lumen into the follicular cells. This process occurs through pinocytosis, a form of endocytosis where the cell membrane invaginates to engulf the substance, forming a membrane-bound vesicle that carries the thyroglobulin into the cytoplasm. Once inside the cell, the thyroglobulin is split by enzymes into its component parts, including the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are then released into the circulation.12