photo.jpg

## Neurocrines - **Synthesized** in neurons of the GI tract, moved by axonal transport down the axons, and released by action potentials in the nerves. - **Diffuse** across the synaptic cleft to a target cell. - **Types:** vasoactive intestinal peptide (VIP), neuropeptide Y, nitric oxide (NO), GRP...

## Neurocrines - **Synthesized** in neurons of the GI tract, moved by axonal transport down the axons, and released by action potentials in the nerves. - **Diffuse** across the synaptic cleft to a target cell. - **Types:** vasoactive intestinal peptide (VIP), neuropeptide Y, nitric oxide (NO), GRP (bombesin), and enkephalins. ### VIP - **Contains** 28 amino acids and is *homologous to secretin*. - **Released** from neurons in the mucosa and smooth muscle of the GI tract. - **Produces** relaxation of GI smooth muscle, including the lower esophageal sphincter. - **Stimulates** pancreatic HCO3- secretion and **inhibits** gastric H+ secretion. - **Resembles** secretin. - **Secreted** by pancreatic islet cell tumors and is presumed to mediate pancreatic cholera. ### GRP (bombesin) - **Released** from vagus nerves that innervate the G cells. - **Stimulates** gastrin release from G cells. ### Enkephalins (met-enkephalin and leu-enkephalin) - **Secreted** from nerves in the mucosa and smooth muscle of the GI tract. - **Stimulate** contraction of GI smooth muscle, particularly the lower esophageal, pyloric, and ileocecal sphincters. - **Inhibit** intestinal secretion of fluid and electrolytes. This action forms the basis for the usefulness of opiates in the treatment of diarrhea.