Türoidotsüüdid

Thyroidocytes are the principal functional cells of the thyroid gland. These epithelial cells are responsible for synthesizing, storing, and secreting thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3). Thyroidocytes are arranged in spherical structures called follicles, which are the basic anatomical and functional units of the thyroid. The lumen of each follicle is filled with colloid, a gel-like substance primarily composed of thyroglobulin, a protein synthesized by the thyroidocytes that serves as a precursor for thyroid hormones.

Within the thyroidocyte, the endoplasmic reticulum and Golgi apparatus are highly developed, reflecting their significant role in protein synthesis and secretion. The apical surface of the thyroidocyte faces the follicular lumen, where it actively takes up iodide from the bloodstream and transports it into the colloid. This iodide is then oxidized and incorporated into tyrosine residues of thyroglobulin in a process called iodination. Subsequently, these iodinated tyrosine residues are coupled to form T3 and T4, which remain bound to thyroglobulin within the colloid.

When stimulated by thyroid-stimulating hormone (TSH) from the pituitary gland, thyroidocytes undergo endocytosis to engulf portions of the colloid. Within the cell, lysosomes fuse with these endocytic vesicles, and the thyroglobulin is degraded, releasing T3 and T4 into the bloodstream. This intricate process allows for precise regulation of thyroid hormone levels in the body, which are crucial for metabolism, growth, and development.