A ring of muscle around a natural opening or passage that acts as a valve, regulating inflow or outflow.
A circular muscle which surrounds the opening from an organ, and, by maintaining a constant state of moderate contraction, prevents the escape of the contents of the organ. Sphincters close the outlet from the URINARY BLADDER and RECTUM, and in certain nervous diseases their action is interfered with, so that the power to relax or to keep moderately contracted is lost, and retention or INCONTINENCE of the evacuation results.
n. a specialized ring of muscle that surrounds an orifice. Contractions of the sphincter partly or completely close the orifice. Sphincters are found, for example, around the anus (anal sphincter) and at the openings between the oesophagus and stomach (lower oesophageal sphincter, LOS) and between the stomach and duodenum (pyloric sphincter).
combining form denoting a sphincter.
(OASIS) a spectrum of injuries that encompasses both third- and fourth-degree *perineal tears. Injury to the anal sphincter mechanism during childbirth may arise secondarily to direct disruption of the sphincter muscles and/or traction of the pudendal nerves. Disruption of the anal sphincter muscles is best assessed by anal ultrasound examination. This is usually performed using a high-frequency (10 MHz) endoanal probe. In selected cases with complex injury and/or suspected rectovaginal *fistula, magnetic resonance imaging (MRI) may also be employed.... obstetric anal sphincter injury
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