Which of the following decreases intestinal motility:March 2011

Ans. D: SecretinThe strength of the contractions of small intestine is propoional to the frequency of the spike generated by the slow waves"Slow wave" amplitude is increased by GIT hormones released during digestion e.g. gastrin, CCK-PZ and motilin; whereas secretin and glucagons decrease the slow wave amplitudeIntestinal motilityDigestive hormones, cholecystokinin (CCK), gastrin and motilin increase intestinal motilitySecretin decreases the activity.Serotonin and insulin can increase motilityGlucagon can decrease motility.SecretinSecretin is synthesized in cytoplasmic secretory granules of S-cells which are found mainly in mucosa of duodenum and smaller numbers in jejunum of small intestineSecretin is released into circulation and/or intestinal lumen in response to low duodenal pH.Also the secretion of secretin is increased by the products of protein digestion bathing the mucosa of the upper small intestine.It is the active form of prosecretin.This acidity is due to hydrochloric acid in the chyme that enters the duodenum from the stomach the pyloric sphincter.Secretin targets the pancreas, which causes the organ to secrete a bicarbonate-rich fluid that flows into the intestine.Bicarbonate ion is a base that neutralizes the acid, thus establishing a pH orable to the action of other digestive enzymes in the small intestine and preventing acid burns.Other factors are also involved in the release of secretin such as bile salts and fatty acids, which result in additional bicarbonates being added to the small intestine.Secretin release is inhibited by H2 receptor antagonists, which reduce gastric acid secretion.As a result, if the pH in the duodenum increases above 4.5, secretin cannot be releasedSecretin increases water and bicarbonate secretion from duodenal Brunner's glands in order to buffer the incoming protons of the acidic chyme.It also enhances the effects of cholecystokinin to induce the secretion of digestive enzymes and bile from pancreas and gallbladder, respectively.It counteracts blood glucose concentration spikes by triggering increased insulin release from pancreas, following oral glucose intake.Although secretin releases gastrin from gastrinomas, it inhibits gastrin release from the normal stomach.It reduces acid secretion from the stomach by inhibiting gastrin release from G cells.In addition, secretin stimulates pepsin secretion from chief cells