Parathyroid Hormones: It is the most important endocrine regulator of calcium and phosphorus concentration in extracellular fluid. This hormone is secreted from cells of the parathyroid glands and finds its major target cells in bone and kidney. Another hormone, parathyroid hormone-related protein, binds to the same receptor as parathyroid hormone and has major effects on development.

Like most other protein hormones, parathyroid hormones is synthesized as a preprohormone. After intracellular processing, the mature hormone is packaged within the Golgi into secretory vesicles, the secreted into blood by exocytosis. Parathyroid hormones is secreted as a linear protein of 84 amino acids.

Physiologic Effects of Parathyroid Hormones

If calcium ion concentrations in extracellular fluid fall below normal, bring them back within the normal range. In conjunction with increasing calcium concentration, the concentration of phosphate ion in blood is reduced. Parathyroid hormone accomplishes its job by stimulating at least three processes:

• Mobilization of calcium from bone: Although the mechanisms remain obscure, a well-documented effect of parathyroid hormone is to stimulate osteoclasts to reabsorb bone mineral, liberating calcium into blood.
• Enhancing absorption of calcium from the small intestine: Facilitating calcium absorption from the small intestine would clearly serve to elevate blood levels of calcium. Parathyroid hormone stimulates this process, but indirectly by stimulating production of the active form of vitamin D in the kidney. Vitamin D induces synthesis of a calcium-binding protein in intestinal epithelial cells that facilitates efficient absorption of calcium into blood.
• Suppression of calcium loss in urine: In addition to stimulating fluxes of calcium into blood from bone and intestine, parathyroid hormone puts a brake on excretion of calcium in urine, thus conserving calcium in blood. This effect is mediated by stimulating tubular reabsorption of calcium. Another effect of parathyroid hormone on the kidney is to stimulate loss of phosphate ions in urine.

What if the parathyroid hormones is too high?

Hyperthyroidism is an endocrine disorder which causes oversecretion of parathyroid hormone in the body. This oversecretion of PTH causes an abnormal rise in the blood calcium levels.

Oversecretion of parathyroid hormone can make a person depressed, irritable, insomnia, memory loss, lack of energy and worried are the most common symptoms in patients with parathyroid disease.

It is of three types.

• Primary hyperparathyroidism
• Secondary hyperparathyroidism
• Tertiary hyperparathyroidism

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By Team Learning Mantras