A sphincter is a ring of muscle around an opening in the body. When it tightens, the opening closes; when it relaxes, the opening lets something through.

A sphincter is a ring of muscle around an opening in the body是身體某個開口周圍的一圈肌肉。When it tightens當它收緊時 the opening closes開口就會關閉 when it relaxes當它放鬆時 the opening lets something through開口就會讓東西通過。

You have many of them: at the bottom of the stomach, where the tube from your mouth joins the stomach, around the bladder, in the eye around the pupil, and — the one most people think of first — at the anus. It is a plain medical noun, countable (one sphincter, two sphincters), and doctors say it without any fuss.

You have many of them你身體裡有很多個 at the bottom of the stomach在胃的下端 where the tube from your mouth joins the stomach也就是從嘴巴連到胃的管子接口那裡 around the bladder在膀胱周圍 in the eye around the pupil在眼睛裡瞳孔周圍 and — the one most people think of first — at the anus還有——大多數人第一個想到的——在肛門那裡。It is a plain medical noun, countable (one sphincter, two sphincters)這是一個普通的醫學名詞，可數（one sphincter、two sphincters） and doctors say it without any fuss醫生說起來完全不會扭捏。

In English, though, the word can raise a laugh or embarrass people, because listeners assume you mean the one at the bottom. Because of that it also has a jokey use: sphincter-tightening, sphincter-clenching, meaning very frightening.

In English, though不過在英文裡 the word can raise a laugh or embarrass people這個字可能會引人發笑或讓人尷尬 because listeners assume you mean the one at the bottom因為聽的人會以為你指的是肛門那個。Because of that正因為如此 it also has a jokey use它也有開玩笑的用法：sphincter-tightening, sphincter-clenching像sphincter-tightening、sphincter-clenching meaning very frightening意思是非常嚇人。

Doctors often name which one they mean — the anal sphincter, the lower oesophageal sphincter (the one whose weakness causes 胃食道逆流). A related word your students may meet is sphincter muscle, which is just the same thing said twice.

Doctors often name which one they mean醫生通常會講清楚是指哪一個 — the anal sphincter, the lower oesophageal sphincter像肛門括約肌、下食道括約肌 (the one whose weakness causes 胃食道逆流)（這一個功能不好就會造成胃食道逆流）。A related word your students may meet is sphincter muscle學生可能還會遇到一個相關的字sphincter muscle which is just the same thing said twice其實就是同一件事講兩次而已。