VIP

Question 1

Neuro endocrine

Answer 1

are synthesized in neurons of the GI tract, moved by axonal transport down the axon, and released by action potentials in the nerves.
■ Neurocrines then diffuse across the synaptic cleft to a target cell.
■ The GI neurocrines are vasoactive intestinal peptide (VIP), GRP (bombesin), and enkephalins.
1. VIP
■ contains 28 amino acids and is homologous to secretin.
■ is released from neurons in the mucosa and smooth muscle of the GI tract.
■ produces relaxation of GI smooth muscle, including the lower esophageal sphincter.
■ stimulatespancreaticHCO3–secretionandinhibitsgastricH+secretion.Intheseactions,it resembles secretin.
■ is secreted by pancreatic islet cell tumors and is presumed to mediate pancreatic cholera.
2. GRP (bombesin)
■ is released from vagus nerves that innervate the G cells. ■ stimulatesgastrinreleasefromGcells.
3. Enkephalins (met-enkephalin and leu-enkephalin)
■ are secreted from nerves in the mucosa and smooth muscle of the GI tract.
■ stimulatecontractionofGIsmoothmuscle,particularlytheloweresophageal,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.