anal sphincter

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a circular muscle that constricts a passage or closes a natural orifice. When relaxed, a sphincter allows materials to pass through the opening. When contracted, it closes the opening. Four main sphincter muscles along the alimentary canal aid in digestion: the cardiac sphincter, the pyloric sphincter, and two anal sphincters. Other sphincters are found in the iris of the eye, the bile duct (sphincter of Oddi), the urinary tract, and elsewhere.
anal sphincter (sphincter a´ni) either of two sphincters (the internal and external anal sphincters) that open and close to control evacuation of feces from the anus.
cardiac sphincter a sphincter between the esophagus and the stomach, opening at the approach of food that can then be swept into the stomach by rhythmic peristaltic waves.
sphincter of Oddi a sheath of muscle fibers investing the associated bile and pancreatic passages as they traverse the wall of the duodenum.
pyloric sphincter a sphincter at the opening from the stomach into the duodenum; it is usually closed, opening only for a moment when a peristaltic wave passes over it.
urinary sphincter, artificial a fluid-filled system that surrounds the urethra with a silicone cuff that functions as a sphincter; a pump is in the scrotum and a fluid reservoir is in the abdomen. For urination, the pump's release valve is squeezed to allow the fluid to leave the urethral cuff and return to the reservoir; after urination is complete, the pump is squeezed and the fluid returns to the cuff to occlude the urethra.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

ex·ter·nal a·nal sphinc·ter

a fusiform ring of striated muscular fibers surrounding the anus, attached posteriorly to the coccyx and anteriorly to the central tendon of the perineum; it is subdivided, often indistinctly, into a subcutaneous part, a superficial part, and a deep part for descriptive purposes.
Farlex Partner Medical Dictionary © Farlex 2012

anal sphincter

A hybrid anatomic structure designed to control the anal opening, which is composed of an internal sphincter and an external spincter. Anal sphincter defects can be induced by forceps delivery.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

anal sphincter

The double muscular ring surrounding the anal canal which, in conjunction with the thick, well-vascularized lining of the canal, produces a watertight seal except during defaecation.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
References in periodicals archive ?
Risk factors for primary and subsequent anal sphincter lacerations: a comparison of cohorts by parity and prior mode of delivery.
The patient regained his muscle power of the lower limbs soon postoperatively after extubation in the intensive care unit, as well as the anal sphincter function.
Hypertrophic myopathy of the internal anal sphincter: a rarely recognized cause of proctalgia.
Women's experience of anal incontinence following a history of obstetric anal sphincter injury: A literature review.
In this study, perineal body thickness, anal sphincter maximum squeezing pressure, mean resting pressure (MRP), external anal sphincter defect (EASD) and sphincter angle were evaluated.
The aims of this study were to prospectively describe the effect of pregnancy and delivery in women without clinical signs of anal sphincter tears, on endosonographic morphology of the anal sphincter and on anal sphincter pressures, and to highlight any differences in these findings between nulliparous and multiparous, Black African and Indian women.
Incidence of obstetric anal sphincter injuries after training to protect the perineum: cohort study.
Raised anal resting pressures caused by hyper tonicity of the internal anal sphincter (IAS) and ischemia of anal canal have been suggested as factors that are important in pathogenesis of anal fissures.3,8
It has been shown that the resting tone of internal anal sphincter is higher in patients of chronic anal fissure.
Their removal can risk damage to the anal sphincter.
Indeed, obstetric anal sphincter injuries (OASIS), (1) with their short-and long-term consequences, merit clinical attention, as spotlighted in Dr.