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Old 02-11-2013
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Question carcinoid tumor


having read about carcinoid tumor, some part that I don't understand..
"The carcinoid tumor is confined to gi system, no carcinoid syndrom is observed, because of metabolism of 5 HT in liver, but when it is metastases (outside GI system), carcinoid syndrome is observed..(FA)"
I don't really understand how 5 HT is metabolized in liver when it is in GI system. (through which way??) why can't it be metabolized when the cancer is located outside GI?

Thanks in advance
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Old 02-11-2013
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Carcinoid tumors are derived from neuroendocrine cells. Function of these cells is to synthesize a variety of peptide & non peptide hormones like seretonin, bradykinin, kallikrein, prostaglandin etc. Most commonly they arise from GIT, but pancreas, gall bladder, Bronchial tissue are also source of these tumor. When carcinoid tumor arise from GIT.......elaboration of these local hormone like substance reach venous circulation & goes to liver. Liver metabolizes serotonin (5-HT) to produce 5-Hydroxyindoleacetic acid (5-HIAA). As a result 5-HIAA level becomes elevated in blood & urine of those suffering from carcinoid tumor. But when liver function gets compromised due to metastasis of primary tumor..............then it will lead to elevated level of 5-HT as well as other metabolites which consequently will result carcinoid syndrome characterized by flushing, diarrhea, dermatitis, bronchoconstriction.
So in case of carcinoid tumor outside the GI system will invariably devolop this systemic syndrome.
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