In addition to thyroxine (T4) and triiodothyronine (T3), the thyroid gland secretes calcitonin from its parafollicular C-cells. Calcitonin lowers blood calcium by inhibiting osteoclast activity and promoting calcium deposition in bone. Parathyroid hormone (PTH) is secreted by the separate parathyroid glands (not the thyroid); somatostatin is from the hypothalamus/pancreas; thyroglobulin is a precursor protein, not a secreted hormone.