Anatomy And Physiology

Anatomy Physiology



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In this article, I will discuss the normal physiology of the parathyroid gland, in addition to two disorders that often affect this gland.  These are hyperparathyroidism and hypoparathyroidosim.  The first disorder refers to excessive secretion of the parathyroid hormone to the circulation by the parathyroid gland and the other disorder refers to deficient secretion of this hormone by the same gland.  These two disorders will be discussed in this article.


There are normally four parathyroid glands that are located in the back of the thyroid gland.  The main function of the parathyroid gland is to secrete the important hormone which is called parathyroid hormone.  This hormone is important for maintaining homeostasis of calcium ions in the blood.


Parathyroid hormone usually functions by stimulating calcium ions resorption from the bone tissue.  In this, it stimulates the release of calcium from the bone to the blood circulation.  It does so by stimulating the bone cells which are called osteoclasts to release calcium ions to the blood circulation. 


An antagonist to the action of parathyroid hormone is called calcitonin and which is secreted by the cells of the thyroid gland.  Calcitonin stimulates the type of cells in the bone and which are called osteoblasts to deposit calcium salts on the bone tissue.  When the level of calcium in the blood is high, calcitonin hormone is released to the circulation causing deposition of calcium on the bone tissue. 


Calcitonin functions by inhibiting the action of osteoclasts of the bone tissue.  Thus decreasing the level of calcium in the blood.  A hypocalcemic state or low level of calcium in the blood stimulates the release of parathyroid hormone from the parathyroid gland.  This condition can occur for example in chronic renal failure in which case the hypocalcemia that occurs stimulates the parathyroid gland to secrete more parathyroid hormone causing a state of hyperparathyroidism that is compensatory to the hypocalcemia due to the renal failure. 


Parathyroid hormone functions also by stimulating the kidney to synthesize the active form of vitamin D, which is called calcitriol.  This compound stimulates the absorption of calcium in the small intestine.  Thus increasing the concentration of calcium in the blood.


Hyperparathyrodism is defined as higher concentration of the parathyroid hormone than a normal range that is usually occurring under normal physiology of this gland.  One cause to this condition is chronic renal failure which was discussed previously in this article. The other cause to hyperparathyroidism is an adenoma which can afect this gland as well as other glands such as the pituitary gland.  Adenomas are usually larger in size than a normal gland.


Another cause to hyperparathyroidism is hyperplastic process that can affect the gland in which case the gland undergoes proliferation of its secreting cells.  Hyperplasia of the parathyroid gland can occur for example due to chronic renal failure which causes hypocalcemia which is the real cause to the hyperplasia.


The third cause to hyperparathyroidism is parathyroid gland carcinoma.  This condition is very rare.  If it occurs it can be characterized by excessive amount of calcium ions in the blood due to excessive resorption of this ion by the action of the parathyroid hormone on the bone osteoclasts. 


In addition to increased amount of parathyroid hormone in the blood that is due to hyperparathyroidism another cause to hyperparathyroidism is ectopic secretion of this hormone due to a malignant tumour elsewhere in the body that secretes this hormone also, in addition to its original source from the parathyroid gland. 


The other medical condition of this gland and which is called hypoparathyroidism is usually caused as a result of surgery to the thyroid gland in which a tumour of the thyroid gland is removed.  This operation can cause blood supply stopping to the parathyroid glands.  Thus causing its damage and subsequent state of hypoparathyroidism.


Another cause to hypoparathyroidism or decreased secretion of the parathyroid hormone is due to damage to the parathyroid gland, which can occur due to an immune disease and can destroy the gland tissues.  This cause to hypoparathyroidism is rare with a slight preponderance for females over males.


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