Thyroid, parathyroid hormones and calcium homeostasis

The thyroid gland secretes thyroxine (T4) and triiodothyronine (T3) in response to thyroid-stimulating hormone release from the anterior pituitary gland. Iodine is essential for the synthesis of thyroid hormones. T4 and T3 increase the basal metabolic rate, heat production, and help to maintain normal growth and development. Serum calcium levels are under very tight control. The majority of calcium is found in bones. Calcium and phosphate levels are maintained by four hormones - parathyroid hormone (PTH), calcitonin, vitamin D and fibroblast growth factor 23. PTH is produced by the parathyroid glands and its secretion is determined by serum calcium levels.