Role of serotonin in the digestive system, artwork. In the gut serotonin (5HT) is produced by enterochromaffin (EC) cells (blue and white cells in upper circle), which are found in the epithelial lining, in response to the presence of food in the lumen. Serotonin acts locally (red lines), on the digestive tract, and also on the central nervous system (CNS, brown lines). Local effects include activating peristalsis and secretory cells. Actions on the CNS include transmitting feelings of abdominal discomfort and bloating, and fullness. For a labelled version of this diagram see C007/1823.