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Most commonly, Acromegaly arises as a result of an anterior pituitary tumor producing excess amounts of GH. On rare occasions, Acromegaly may also result from ectopic tumors producing excess GH or GHRH .
The pituitary tumor arises from an overgrowth of the GH producing cells (somatotrophs) within the anterior pituitary gland. These tumors manufacture and secrete excessive amounts of growth hormone continuously. They are not subject to the usual feedback inhibitory (Somatostatin)/stimulatory (GHRH) mechanism within the pituitary that regulates GH levels precisely in health.
These abnormally high GH levels both directly and indirectly (through IGF-1) are responsible for the condition of Acromegaly. In up to 30% of cases of Acromegaly, excess prolactin (PRL) hormone is also secreted from the pituitary, either by tumor cells that have the ability to secrete both hormones ( somatomammotrophs ) or separately from prolactin secreting cells( lactotrophs ).
The reasons for the abnormal growth of pituitary growth hormone secreting cells to form a tumor are several. These include excess GHRH production from the hypothalamus , intra-cellular gene defects and possibly together with a reduction in the level of SRIF.
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