The thyroid gland regulates calcium homeostasis through a complex interplay of parathyroid hormone (PTH), calcitonin, and calcitriol (vitamin D). PTH increases blood calcium by promoting bone resorption and renal reabsorption. Calcitonin decreases blood calcium by inhibiting bone resorption. Calcitriol stimulates intestinal calcium absorption. Together, these hormones tightly control blood calcium levels through effects on bone, kidney, and intestine. Imbalances can lead to hyperparathyroidism, hypoparathyroidism, or vitamin D deficiency disorders.

1. Thyroid gland The name "thyroid" comes from the Greek word which means "shield"

10. Steps of thyroid hormone synthesis Iodine trapping (using iodide pump); thyroglobulin synthesis; oxidation of iodide to iodine; iodination of tyrosine molecules within the thyroglobulin molecule to give MIT and DIT at the apical border of the cell; coupling of MIT and DIT to give T3 and T4 still within the thyroglobulin molecule in the colloid; pinocytosis of thyroglobulin and proteolysis of thyroglobulin and release of T3 and T4

14. Effects of Thyroid Hormone on Basal Metabolic rate T 3 GI activity Fat and carbohydrate mobilization Heart rate BMR Metabolic waste products Oxygen consumption Metabolic fuels Cardiac output Respiration Active hyperemia

31. Calcium pool