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at the junction of the esophagus and stomach
lower-esophageal-sphincter
The lower esophageal sphincter must open to permit vomiting.
cardiac sphincter; or
gastroesophageal sphincter; or
lower esophageal sphincter (LES); or
esophageal sphincter
from http://en.wikipedia.org/wiki/Cardia
cardiac sphincter/lower esophageal sphincter (LES)
lower esophageal sphincter.