Tone of lower esophageal sphincter is increased by-

Ans. is 'c' i.e., Acetylcholine Lower esophageal sphinctero Unlike the rest of the esophagus, the musculature of the gastroesophageal junction (lower esophageal sphincter: LES) is tonically active but relaxes on swallowing,o The tonic activity of the LES between meals prevents reflux of gastirc contents into the esophagus,o The LES is made up of three components.o The esophageal smooth muscle is more prominent at the junction with the stomach (intrinsic sphincter),o Fibers of the crural portion of the diaphragm, a skeletal, a skeletal muscles, surround the esophagus at this point (extrinsic sphincter) and exert a pinchcock-like action on the esophagus. In addition, the oblique or sling fibers of the stomach wall create a flap valve that helps close off the esophagogastric junction and prevent regurgitation when intragastric pressure rises,o The tone of the LES is under neural control.o Release of acetylcholine front vagal endings causes the intrinsic sphincter to contact, and release of NO and VIP from interneurons innervated by other vagal fibers causes it to relax.o Contraction of the crural portion of the diaphragm, which is innervated by the phrenic nerves, is coordinated with respiration and contractions of chest and abdominal muscles,o Thus, the intrinsic and extrinsic sphincters operate together to permit orderly flow' of food into the stomach and to prevent reflux of gastric contents into the esophagus.