 Dear students, in this topic we shall discuss the parathyroid gland and its hormones. The parathyroid glands are tiny pea-sized glands which are embedded in the thyroid gland. Each lobe of thyroid has two parathyroid glands embedded in it. The parathyroid glands produce the hormone which is called paratharmon or PTH. Paratharmon is released in response to drop in plasma calcium levels. It regulates the concentration of calcium and phosphate ions in the blood. It increases plasma calcium level by promoting calcium ions mobilization from the bones. It also promotes calcium reabsorption from the kidneys and decreases the amount of calcium loss in the urine. Paratharmon also enhances calcium absorption from small intestine into the blood. It regulates phosphate ions in the blood by their absorption into the bone and enhances their renal excretion. Paratharmon regulates calcium and phosphate in the opposite ways. It raises the level of calcium in the blood by absorbing the calcium from the kidneys as well as phosphates. Dear students, the paratharmon acts with the help of calcium triole. Calcium triole is the active form of vitamin D. Vitamin D is converted into calcium triole by the action of paratharmon on the kidneys where it enhances the hydroxylase activity of kidneys which metabolize vitamin D and produce calcium triole. Calcium triole, after its production, works with paratharmon and stimulates calcium reabsorption and phosphate excretion through the kidneys. Calcium triole also helps in the release of calcium ions from the bones and its absorption from the gut. Dear students, over production of paratharmon has certain drastic effects on bones. Bones become soft and deformed and prone to fracture because of overscretion of paratharmon. Elevation of this paratharmon really extra over production of paratharmon also results in the elevation of blood calcium levels i.e. hypercalcemia. It also results in the suppression of nervous system and weakness of muscles due to hypercalcemia. Hypercalcemia results in production of kidney stones because in kidneys extra calcium salts are precipitated and converted into stones. The undersecretion of PTH also has bad effects. It produces hypocalcemia when the level of calcium in the blood is reduced. The undersecretion of paratharmon also causes increased excitability of neurons. It also results in muscle tattany in which the muscles remain in contracted state.