| Like other forms of connective tissue, the bone is | | | | - Another mechanism is slower and is dependent on |
| composed of cells and fibers. Unlike the other types of | | | | the activation of osteoclasts. This mechanism could |
| connective tissue, however, the bone has higher | | | | take days to weeks because osteoclasts are not |
| amounts of calcium deposits, making it harder. This | | | | directly stimulated by parathyroid hormone. Instead, |
| unyielding structure of bone enables it to perform its | | | | they receive signals from the osteocytes to increase |
| functions of support and protection. | | | | bone resorption. |
| The physical properties of bone are nothing short of | | | | |
| amazing. Aside from maintaining great strength, bone is | | | | Bone Disease in Hyperparathyroidism |
| also capable of some degree of elasticity while being | | | | Normally, there is a strict balance maintained between |
| surprisingly lightweight. From its gross structure to | | | | bone deposition by osteoblasts and bone resorption by |
| microscopic levels, bone construction was designed for | | | | the osteoclasts. Even in mild hyperparathyroidism, the |
| great strength while maintaining a great economy for | | | | activity of osteoblasts can compensate for the slight |
| material and weight. | | | | increase in bone resorption caused by activated |
| However, despite its apparent toughness, bone is a | | | | osteoclasts. However, in severe hyperparathyroidism, |
| living structure. It responds to metabolic and nutritional | | | | bone resorption far outweighs the formation of new |
| changes as well as endocrine influences. Bone | | | | bone and the bone may be eaten away entirely. It is |
| undergoes constant reorganization while maintaining a | | | | for this reason that bone fractures are commonly the |
| certain degree of hardness necessary for its | | | | reason a hyperparathyroid patient seeks medical help. |
| supportive and protective functions. | | | | In cases of extremely high levels of parathyroid |
| Parathyroid Hormones | | | | hormone, radiographs of bones reveal extensive |
| Parathyroid hormone is responsible for controlling the | | | | decalcification and large punched-out areas filled with |
| extracellular calcium and phosphate concentrations. It | | | | osteoclasts in the form of giant cell osteoclast |
| does so by regulating intestinal reabsorption, renal | | | | “tumors”. This means that the bone structure is |
| excretion and the exchange between the extracellular | | | | extremely weakened by excessive resorption that |
| fluid and the bone. | | | | even slight trauma can result in multiple fractures. The |
| Parathyroid hormones are produced by the | | | | cystic bone disease of hyperparathyroidism is called |
| parathyroid glands located posterior to the thyroid | | | | osteitis fibrosa cystica. |
| gland. Normally, humans possess four parathyroid | | | | Primary hyperparathyroidism is caused by an |
| glands but in some cases, there could be as many as | | | | abnormality in the parathyroid glands themselves. |
| six. Removal of half the number of parathyroid glands | | | | Usually, the increased activity of the parathyroid glands |
| may not affect the normal physiology much. However, | | | | are caused by tumors, which actively secrete |
| the removal of three out of four of the normal glands | | | | parathyroid hormone. These tumors are more |
| may result in transient hypothyroidism. This means that | | | | common in women than in men. |
| even if only one of the parathyroid glands remain, it | | | | Secondary hyperparathyroidism, on the other hand, |
| can compensate for the loss of the other three glands. | | | | occurs as a compensatory mechanism for low |
| Parathyroid hormone acts on bone to elevate the | | | | calcium levels. This then signals the parathyroid glands |
| levels of calcium in circulation in two ways: | | | | to increase secretion of parathyroid hormone to |
| | | | | replenish the depleted calcium ion in the circulation with |
| - One is a rapid phase that calls on bone cells or | | | | calcium derived from deposits in the bone. Secondary |
| osteocytes and proceeds in a matter of minutes to | | | | hyperparathyroidism can be caused by vitamin D |
| several hours. Existing osteocytes in the bone matrix | | | | deficiency or chronic renal disease, in which the |
| pump calcium ions from the bone fluid into the | | | | kidneys are too damaged to produce the active form |
| extracellular fluid, increasing the circulating calcium ions | | | | of vitamin D in sufficient amounts. |
| in circulation. | | | | |