Major initiating response for peristalsis is -

Ans, is 'b' i.e., Local stretching of gut o The propulsive movement of the small intestine are called peristalsis0.o Peristalsis consists of a ring of contraction in one segment, and receptive relaxation in the immediatly distal segment.oThis results in propulsion of contents from the contracted segment to the relaxed segment.o This is promptly followed by contraction of the segment which was earlier relaxed and relaxation of the segment which is distal to it.o Thus a wave of contraction travels distally, resulting in propulsion of the contents,o Peristalsis is a local stretch reflex and the usual stimulus for peristalsis is distention of the gutQ,o Peristalsis requires an active myenteric (Auerbach's) plexusQ.o Local stretch by chyme releases serotonin, which activates myenteric plexus.o Cholinergic neurons of this plexus passing in a retrograde direction release substance P and acetylcholineQ,causing smooth muscle contraction.o Cholinergic neurons passing in an antegrade direction activate neurons that secrete NO, VIP, and ATP, produing relaxation ahead of the stimulus.o In addition to nervous signals, several hormonal factors also affect peristalsis.o Gastrin, Cholecystokinin0 insulin, motilin and serotonin enhance intestinal motility,o Secretin and glucagon inhibit small intestinal motility.