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Sphincter - Definition


The sphincter is a generally ring-shaped muscle that lines an orifice, usually controlling its opening and closing with different mechanisms of muscular contraction. There are several different sphincters in the body, notably in the esophagus, anus, and bladder, among others. When these sphincters contract, they close the tube they control, which prevents whatever content it holds from progressing. When they relax, the passage is cleared. When there are abnormalities in the function of the bladder or anal sphincter, this can lead to involuntary secretion of urine or fecal matter, in which case it is called sphincter incontinence. When it is the esophageal sphincter that is affected, the ball of food cannot correctly pass through, in which case a condition called achalasia often occurs, which leads to the feeling of digestive regurgitation.