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.

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.

anal sphincter

either of two sphincters (the internal and external anal sphincters) that open and close to control the evacuation of feces from the anus.

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.

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.


relating to the anus.

anal abscess
acute, purulent infections in the area of the anus, usually caused by gram-negative organisms. In dogs, these most often arise from the anal sacs.
anal atresia, atresia ani
congenital absence or stenosis of the anus manifested by an absence of feces and a gradual development of abdominal distention. Fistulae may develop between the rectum and urogenital tract. The anomalous development can occur in several forms and may be accompanied by similar atresia at higher levels of the intestine. There is usually normal development of sphincters. A dimple is usually evident at the point at which surgical intervention is required.
anal canal
the short, terminal, retroperitoneal segment of the intestinal tract between the rectum and anus.
anal constriction
a congenital constriction combined with vulvar constriction occurs in Jersey cattle.
anal fibroma
occurs in cattle and excision effected for esthetic reasons.
anal fistula
see perianal fistula.
anal fold
see anal fold.
anal furunculosis
see perianal fistula.
anal membrane
the dorsal part of the cloacal membrane in the embryo; when it eventually breaks down the dorsal passage becomes the rectoanal passage.
anal-perineal laceration
see rectovaginal fistula.
anal prolapse
the protrusion of a small amount of mucosa through the anus.
anal reflex
the pursing of the anal orifice when the perineum is stimulated; indicative of an animal with intact sacral segments of the spinal cord.
anal sac
see anal sacs.
Enlarge picture
Anal sacs in the dog. By permission from McCurnin D, Poffenbarger EM, Small Animal Physical Diagnosis and Clinical Procedures, Saunders, 1991
anal sacculitis
inflammation of the anal sacs.
anal sphincter
the internal anal sphincter is formed from smooth muscle of the anal canal while the external anal sphincter, which is larger and of greater importance in fecal continence, consists of striated muscle.
anal sphincter hypertrophy
occurs in aged dogs and may give rise to difficult and painful defecation.
anal stenosis
scar formation after perianal fistulae, trauma, severe anal sac disease, or treatment for neoplasia may result in a reduced lumen and particularly a loss of the capacity to dilate with passage of feces. Straining, passage of ribbon-like feces and constipation result.
anal ulceration
inflammation and ulceration of the perianal skin which may be associated with anal sac disease. Seen most commonly in German shepherd dogs.
References in periodicals archive ?
Surgery typically involves cutting a small part of the anal sphincter muscle to prevent spasms.
Major Finding: Nineteen percent of women who had vaginal delivery and anal sphincter laceration met the criteria for AI according to the EPIQ.
Fresh stool leaks without warning around impacted stool due to reduced sensation and involuntary relaxation of the anal sphincter.
Occult anal sphincter injuries-myth or reality Electronic version]?
Important methods that were used included monitoring contractions of the anal sphincter, pelvic floor, abdomen, and legs.
An anal sphincter tear was also more likely to occur in women who had an episiotomy or a forceps assisted birth than women who did not receive these procedures.
These little sacs, around the size of a kidney bean, sit on either side of and just below the anus, between the skin and the anal sphincter muscle.
The external genitalia and the urogenital diaphragm are found within the urogenital triangle, while the anal triangle is composed of the centrally placed anal canal encircled by the external anal sphincter and flanked laterally and posteriorly by the ischiorectal fossae (Figure 3).
San Francisco, CA; 650-616-2200) announced that the United States Patent and Trademark Office has issued a patent (United States 6,395,736) that covers methods of treating anorectal disorders by administering certain concentrations of topical potassium channel openers to the anorectal region in order to decrease abnormally high pressure of the anal sphincter muscle.
Measuring resting pressure in the anal sphincter, the researchers found that GTN effectively reduced the pressure, producing a "chemical sphincterotomy.