<unk>  <unk> , also called parathormone or parathyrin, is a peptide<unk>  secreted by the<unk>  glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine.<unk>  influences bone remodeling, which is an ongoing process in which bone tissue is alternately resorbed and rebuilt over time.<unk>  is secreted in response to low blood serum calcium (Ca2+) levels.<unk>  indirectly stimulates osteoclast activity within the bone matrix (osteon), in an effort to release more ionic calcium (Ca2+) into the blood to elevate a low serum calcium level. The bones act as a (metaphorical) "bank of calcium" from which the body can make "withdrawals" as needed to keep the amount of calcium in the blood at appropriate levels despite the ever-present challenges of metabolism, stress, and nutritional variations.<unk>  is "a key that unlocks the bank vault" to remove the calcium.<unk>  is secreted primarily by the chief cells of the<unk>  glands. It is a polypeptide containing 84 amino acids, which is a prohormone. It has a molecular mass around 9500 Da. Its action is opposed by the<unk>  calcitonin. There are two types of<unk>  receptors.<unk>  1 receptors, activated by the 34 N-terminal amino acids of<unk> , are present at high levels on the cells of bone and kidney.<unk>  2 receptors are present at high levels on the cells of central nervous system, pancreas, testes, and placenta. The half-life of<unk>  is about 4 minutes. Disorders that yield too little or too much<unk> , such as hypoparathyroidism, hyperparathyroidism, and paraneoplastic syndromes can cause bone disease, hypocalcemia, and hypercalcemia.
Parathyroid hormone
Calcitriol
Growth hormone
Calcitonin
Thyroglobulin
Orexin
Calcitonin gene-related peptide
Estrogen 