Sitemap

health advisory Hospital Diseases 2007-11-12 17:57:16

Answer:

Parathyroid hormone (PTH) is secreted by the parathyroid glands. It has several actions, but perhaps the most important is to defend against hypocalcemia. Parathyroid cells sense decreases in plasma Ca and, in response, release preformed PTH into the circulation. PTH increases plasma Ca within minutes by increasing renal and intestinal absorption of Ca and by rapidly mobilizing Ca and PO4 from bone (bone resorption). Renal Ca excretion generally parallels Na excretion and is influenced by many of the same factors that govern Na transport in the proximal tubule. However, PTH enhances distal tubular Ca reabsorption independently of Na. PTH also decreases renal PO4 reabsorption and thus increases renal PO4 losses. Renal PO4 loss prevents the solubility product of Ca and PO4 from being exceeded in plasma as Ca levels rise in response to PTH.

PTH also increases plasma Ca by stimulating conversion of vitamin D (see Vitamin Deficiency, Dependency, and Toxicity: Vitamin D) to its most active form, 1,25(OH)2D. This form of vitamin D increases the percentage of dietary Ca absorbed by the intestine. Despite increased Ca absorption, long-term increases in PTH secretion generally result in further bone resorption by inhibiting osteoblastic function and promoting osteoclastic activity. PTH and vitamin D both function as important regulators of bone growth and bone remodeling

Please see the web pages for more details on Parathyroid hormone.

---

The sole purpose of the parathyroid glands is to control calcium within the blood in a very tight range between 8.5 and 10.2. In doing so, parathyroids also control how much calcium is in the bones, and therefore, how strong and dense the bones are. Although the parathyroid glands are located next to (and sometimes inside) the thyroid gland, they have no related function. The thyroid gland regulates the body鈥檚 metabolism and has no effect on calcium levels while parathyroid glands regulate calcium levels and have no effect on metabolism. Calcium is the element that allows the normal conduction of electrical currents along nerves--its how our nervous system works and how one nerve 'talks' to the next. Our entire brain works by fluxes of calcium into and out of the nerve cells. Calcium is also the primary element which causes muscles to contract.

---

Parathyroid hormone acts on the intestines, kidneys and bones. Its secretion depends upon the level of calcium and phosphate in the blood. In the intestine, calcium absorption is increased and phosphate absorption is decreased. In the kidneys, calcium absorption is increased and phosphate excretion is increased. In the bones, it enhances the activity of both osteoblasts and osteoclasts to remodel bone. Osteoblasts increase calcium depositin in bone, while osteoclasts remove calcium from the bones. This is as simple as I can make it.

---