Thyroid Gland

The Thyroid gland has iodine-containing hormones, tri-iodothyronine (T3) and thyroxine (tetra-iodothyronine T4). They are involved in growth, cell differentiation, the control of oxygen consumption, and the basal metabolic rate in the body. It also produces calcitonin through the parafollicular cells, or C cells. Calcitonin lowers blood calcium levels.

• A thyroid follicle is the structural and functional unit of the gland. The central lumen contains a colloid substance rich in thyroglobulin. It produces the T3/T4 hormones, as well as causing the uptake of inorganic iodide from the blood, synthesis of thyroglobulin, and endocytosis of iodinated thyroglobulin. Lysosomal enzymes degrade iodothyroglobulin to release T3. Thyroid hormones are then released.
• Synthesis of thyroglobulin involved oxidizing iodide by thyroid peroxidase and incorporating the iodide into the thyroglobulin.