The pharyngoesophageal sphincter.
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004947:Esophagus / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008875:Middle Aged; D009132:Muscles / Q000033:anatomy & histology; D010614:Pharynx / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D011859:Radiography