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## Paracrines * are released from endocrine cells in the GI mucosa. * diffuse over short distances to act on target cells located in the GI tract. * The GI paracrines are somatostatin and histamine. ### Somatostatin * is secreted by cells throughout the GI tract in response to $H^+$ in the lumen....

## Paracrines * are released from endocrine cells in the GI mucosa. * diffuse over short distances to act on target cells located in the GI tract. * The GI paracrines are somatostatin and histamine. ### Somatostatin * is secreted by cells throughout the GI tract in response to $H^+$ in the lumen. Its secretion is inhibited by vagal stimulation. * inhibits the release of all GI hormones. * inhibits gastric $H^+$ secretion. ### Histamine * is secreted by mast cells of the gastric mucosa. * increases gastric $H^+$ secretion directly and by potentiating the effects of gastrin and vagal stimulation.