Which of the following statement regarding lower esophageal sphincter is TRUE?
During swallowing when the peristaltic wave sweep down the esophagus the gastroesophageal sphincter relaxes so that the bolus of food can pass into the stomach. the lower esophageal sphincter is tonically active but relaxes on swallowing. This tonic activity of the LES between meals prevents reflux of gastric contents into the esophagus. its tone is under neural control by the parasympathetic nervous system. Contraction of LES is caused by the release of acetylcholine from the vagus and release of NO and VIP from interneurons innervated by other vagal fibers causes it to relax. Ref: Fundamentals of Human Physiology By Lauralee Sherwood page 447. Ganong's Review of Medical Physiology, 24e CHAPTER 27.
It has no tonic activity
It has a tone which is provided by the sympathetic system
Relaxes on increasing abdominal pressure
Relaxes ahead of the peristaltic wave