<P> Control of the digestive system is also maintained by ENS, which can be thought of as a digestive brain that can help to regulate motility, secretion and growth . Sensory information from the digestive system can be received, integrated and acted upon by the enteric system alone . When this occurs, the reflex is called a short reflex . Although this may be the case in several situations, the ENS can also work in conjunction with the CNS; vagal afferents from the viscera are received by the medulla, efferents are affected by the vagus nerve . When this occurs, the reflex is called vagovagal reflex . The myenteric plexus and submucosal plexus are both located in the gut wall and receive sensory signals from the lumen of the gut or the CNS . </P> <P> For further information see Gastrointestinal hormone </P> <P> GI peptides are signal molecules that are released into the blood by the GI cells themselves . They act on a variety of tissues including the brain, digestive accessory organs, and the GI tract . The effects range from excitatory or inhibitory effects on motility and secretion to feelings of satiety or hunger when acting on the brain . These hormones fall into three major categories, the gastrin and secretin families, with the third composed of all the other hormones unlike those in the other two families . Further information on the GI peptides is summarized in the table below . </P> <Table> General GI peptide information <Tr> <Th> </Th> <Th> Secreted by </Th> <Th> Target </Th> <Th> Effects on endocrine secretion </Th> <Th> Effects on exocrine secretion </Th> <Th> Effects on motility </Th> <Th> Other effects </Th> <Th> Stimulus for release </Th> </Tr> <Tr> <Td> Gastrin </Td> <Td> G Cells in stomach </Td> <Td> ECL cells; parietal cells </Td> <Td> None </Td> <Td> Increases acid secretion, increases mucus growth </Td> <Td> Stimulates gastric contraction </Td> <Td> None </Td> <Td> Peptides and amino acids in lumen; gastrin releasing peptide and ACh in nervous reflexes </Td> </Tr> <Tr> <Td> Cholecystokinin (CCK) </Td> <Td> Endocrine I cells of the small intestine; neurons of the brain and gut </Td> <Td> Gallbladder, pancreas, gastric smooth muscle </Td> <Td> None </Td> <Td> Stimulates pancreatic enzyme and HCO3 - secretion </Td> <Td> Stimulates gallbladder contraction; inhibits stomach emptying </Td> <Td> Satiety </Td> <Td> Fatty acids and some amino acids </Td> </Tr> <Tr> <Td> Secretin </Td> <Td> Endocrine S cells of the small intestine </Td> <Td> Pancreas, stomach </Td> <Td> None </Td> <Td> Stimulates pancreatic and hepatic HCO3 - secretion; inhibits acid secretion; pancreatic growth </Td> <Td> Stimulates gallbladder contraction; Inhibits stomach emptying </Td> <Td> None </Td> <Td> Acid in small intestine </Td> </Tr> <Tr> <Td> Gastric inhibitory Peptide </Td> <Td> Endocrine K cells of the small intestine </Td> <Td> Beta cells of the pancreas </Td> <Td> Stimulates pancreatic insulin release </Td> <Td> Inhibits acid secretion </Td> <Td> None </Td> <Td> Satiety and lipid metabolism </Td> <Td> Glucose, fatty acid, and amino acids in small intestine </Td> </Tr> <Tr> <Td> Motilin </Td> <Td> Endocrine M cells in small intestine </Td> <Td> Smooth muscle of stomach and duodenum </Td> <Td> None </Td> <Td> None </Td> <Td> Stimulates migrating motor complex </Td> <Td> Action in brain, stimulates migratory motor complex </Td> <Td> Fasting: cyclic release every 1.5--2 hours by neural stimulus </Td> </Tr> <Tr> <Td> Glucagon - like peptide - 1 </Td> <Td> Endocrine cells in small intestine </Td> <Td> Endocrine pancreas </Td> <Td> Stimulates insulin release; inhibits glucagon release </Td> <Td> Possibly inhibits acid secretion </Td> <Td> Slows gastric emptying </Td> <Td> Satiety; various CNS functions </Td> <Td> Mixed meals of fats and carbohydrates </Td> </Tr> </Table>

What muscular contractions are part of the tract