Thyroid,parathyroid hormones and calcium homeostasis

The thyroid gland secretes thyroxine (T4) and triiodothyronine (T3) in response to thyroid-stimulating hormone (TSH) released from the anterior pituitary gland. Iodine is essential for the synthesis of thyroid hormones. T4 and T3 increase basal metabolic rate, heat production and help to maintain normal growth and development. The parathyroid glands are essential for maintaining normal levels of serum calcium, which is necessary to maintain normal cellular function via calcium acting as a secondary messenger. Calcium is also involved in the coagulation of blood, transmission of nerve impulses and muscular contraction. Calcium is provided by various dietary sources and plasma levels are altered by varying absorption in the gut, mobilization from bone and excretion by the kidney.