Pheochromocytomas are endocrine tumors that are characterized by production of certain chemicals
(catecholamines) normally produced by the endocrine cells
(chromaffin cells) from which the tumors are derived. There are two important catecholamines produced by these chromaffin cells:
norepinephrine and
epinephrine. Norepinephrine, or noradrenaline as it is also known, is a catecholamine produced and released as a neurotransmitter by certain nerves in the brain
(central nervous system noradrenergic nerves) and also in the body
(sympathetic nerves). Sympathetic nerves innervate the blood vessels and the heart to control blood pressure and cardiac function. Norepinephrine is also formed in the adrenal medulla, the central part of the adrenal gland, but here it is further metabolized to another catecholamine called epinephrine or adrenaline. The epinephrine produced and released by the adrenal gland functions as a hormone; it acts principally at sites distant from its site of release from the adrenal medulla. This contrasts with the norepinephrine released by nerves which acts to control the function of the cells at the sites in the immediate proximity of the nerve endings from which the transmitter is released. It is the elevations of one or both norepinephrine or epinephrine in the bloodstream that cause the distinctive but variable symptoms of pheochromocytoma.
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One diagnostic test used in the past for a pheochromocytoma is to administer
[ فقط المشتركين فى المنتدى يمكنهم رؤية الرابط . اضعط هنا للتسجيل ... ] (Catapres®), a centrally-acting alpha-2 agonist used to treat high blood pressure. Clonidine mimics catecholamines in the brain, causing it to reduce the activity of the sympathetic nerves controlling the adrenal medulla. A healthy adrenal medulla will respond to clonidine by reducing catecholamine production; the lack of a response is evidence of pheochromocytoma.
[ فقط المشتركين فى المنتدى يمكنهم رؤية الرابط . اضعط هنا للتسجيل ... ] يعني راح يستعملو في تحديد سرطان Pheochromocytomas ؟؟؟؟؟؟؟؟
العرض العادي
