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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[TA]
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.
either of two sphincters (the internal and external anal sphincters) that open and close to control the evacuation of feces from the anus.
anal sphincterA 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 sphincterThe 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.
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.
the short, terminal, retroperitoneal segment of the intestinal tract between the rectum and anus.
a congenital constriction combined with vulvar constriction occurs in Jersey cattle.
occurs in cattle and excision effected for esthetic reasons.
see perianal fistula.
see anal fold.
see perianal fistula.
the dorsal part of the cloacal membrane in the embryo; when it eventually breaks down the dorsal passage becomes the rectoanal passage.
see rectovaginal fistula.
the protrusion of a small amount of mucosa through the anus.
the pursing of the anal orifice when the perineum is stimulated; indicative of an animal with intact sacral segments of the spinal cord.
see anal sacs.
inflammation of the anal sacs.
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.
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.
inflammation and ulceration of the perianal skin which may be associated with anal sac disease. Seen most commonly in German shepherd dogs.