SEROTONIN (5-HYDROXYTRYPTAMINE 5-HTD o a brain neurotransmitter and an important regulatory factor in the gastrointestinal (Gi)tract and other organ systems o More than 90% of the bodys 5-HT is synthesized in the gut, where 5-HT activates as many as 14 different 5-HT receptor subtypes located on enterocytes enteric neurons. and immune cell and secretory reflexes, platelet aggregation, immune responses, and bone otor o As such, gut-derived 5-HT regulates diverse functions, including enteric motor development, and cardiac function o Dysregulation of peripheral 5-hT is implicated in the pathogenesis of several diseases, including irritable bowel syndrome(BS)(肠易激综合 征) cardiovascular disease(心血管疾病), and osteoporosis(骨质疏松 症) o 5-HT is synthesized by specialized endocrine cells, called mast cells(黏膜肥大细胎(场嗜铬细胞)(ECs), as well as mucosal enterochromaffin ce and myenteric neurons s(肠肌间神经)SEROTONIN (5-HYDROXYTRYPTAMINE [5-HT])  a brain neurotransmitter and an important regulatory factor in the gastrointestinal (GI) tract and other organ systems.  More than 90% of the body’s 5-HT is synthesized in the gut, where 5-HT activates as many as 14 different 5-HT receptor subtypes located on enterocytes , enteric neurons, and immune cells.  As such, gut-derived 5-HT regulates diverse functions, including enteric motor and secretory reflexes, platelet aggregation, immune responses , and bone development, and cardiac function.  Dysregulation of peripheral 5-HT is implicated in the pathogenesis of several diseases, including irritable bowel syndrome (IBS) （肠易激综合 征）,cardiovascular disease（心血管疾病） , and osteoporosis（骨质疏松 症）.  5-HT is synthesized by specialized endocrine cells, called enterochromaffin cells (肠嗜铬细胞) (ECs), as well as mucosal mast cells （黏膜肥大细胞）and myenteric neurons（肠肌间神经）