system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Lower esophageal sphincter
assistant
The correct answer is  Lower esophageal sphincter (LES) The resting pressure is about 20 mm Hg. Basal tone regulated by both intrinsic and extrinsic nerves, and hormones. A significant fraction of this basal tone is mediated by vagal cholinergic fibers (contraction of LES). Hence, options A & B are not correct. Stimulation of sympathetic nerves to the sphincter causes the LES to contract. Relaxation LES occurs in response to primary peristalsis in the esophagus is mediated by VIP and NO. Contraction of the diaphragm or increased intra-abdominal pressure will increase the pressure in LES. Option C is not correct.