That hormone is vitamin D.
Calcitonin
The main primary target tissue of the Parathyroid hormone is the bone, but the kidneys are a target as well.
Parathyroid hormone is a hormone secreted by the Parathyroid glands. It increases the concentration of calcium in the blood. It effects bone, kidney and intestine tissue.
Calcetonin is a hormone that stimulates the absorption of serum calcium by bone tissue. It is an antagonist of Parathyroid Hormone, which stimulates the release of calcium from bone tissue into the blood stream to make it available for muscle contractions, neural impulses, and assisting in blood clotting factors.Source: Medical-Nursing Care, 3rd ed.
Leptin is a hormone released by adipose tissue.
Because they Thyroid makes its own natural hormones. When it was removed the body needed a new place for the hormones to come from.Actually, the thyroid itself has little to do with calcium. so the answer is only partially correct. Embedded in the thyroid tissue there are 4 little glands, the parathyroids. These produce a hormone called parathyroid hormone or PTH. PTH stimulates calcium absorption in the instestine, calcium reabsorption in the kidneys and liberates calcium from the bones. Hence the need for the calcium supplement.The thyroid gland produces many hormones that are necessary for normal body function. When the gland is removed (a thyroidectomy) the deficiency of these hormones results in hypothyroidism without external treatment - hormone therapy. Calcium (and vitamin D) are necessary to prevent hypocalcemia secondary to hypoparathyroidism, that is, a low level of of calcium in the blood (very serious) due to insuffient parathyroid hormone levels (parathyroid hormone functions to increase blood levels of calcium).
Chemorecptors in blood measure the Ca level If there is too little Ca, the parathyroid releases its hormone to release Ca from bone tissue (termed osteoclast), once levels are back to body norm, inhibitory hormone tells the parathyroid hormone to stop releasing its hormone
Prostaglandins are the group of hormones referred to as tissue hormones.
A tissue becomes a target tissue when it is affected or stimulated by a specific amino acid. The target tissue has the appropriate receptors to make it susceptible to the hormone.
The hormone Calcitonin has the effect of reducing blood calcium levels. The hormone comes from the thyroid gland and works in basically three ways. 1. It works to slow absorption of calcium by the intestine. 2. It also inhibits the osteoclast (cells in bone that break down old bone tissue) that raise blood calcium levels. 3. It causes osteoblast (cells in bone that lay down new bone matrix) to form new bone. This explanation is at it's simplest form of course.
Target tissue
The parathyroid gland produces parathyroid hormone (PTH), which regulates the blood calcium level. When blood calcium is low, PTH is secreted and stimulates the digestion of bone tissue by osteoclasts, this releases calcium from the bone into the bloodstream. Calcitonin has the opposite effect of PTH, and is released from the thyroid gland when blood calcium is too high.