anal sphincter

sphincter /sphinc·ter/ (sfingk´ter) [L.] a ringlike muscle which closes a natural orifice or passage.sphinc´teralsphincter´ic

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anal sphincter , sphincter a´ni sphincter muscle of anus (external or internal).

cardiac sphincter , cardioesophageal sphincter muscle fibers about the opening of the esophagus into the stomach.

external sphincter of female urethra  external sphincter muscle of female urethra.

external sphincter of male urethra  external sphincter muscle of male urethra.

gastroesophageal sphincter  the terminal few centimeters of the esophagus, which prevents reflux of gastric contents into the esophagus.

hepatic sphincter  a thickened portion of the muscular coat of the hepatic veins near their entrance into the inferior vena cava.

internal sphincter of urethra  internal sphincter muscle of urethra.

O'Beirne's sphincter  a band of muscle at the junction of the sigmoid colon and rectum.

sphincter of Oddi  the sheath of muscle fibers investing the associated bile and pancreatic passages as they traverse the wall of the duodenum.

pharyngoesophageal sphincter  a region of higher muscular tone at the junction of the pharynx and esophagus, which is involved in movements of swallowing.

precapillary sphincter  a smooth muscle fiber encircling a true capillary where it originates from the arterial capillary, which can open and close the capillary entrance.

pyloric sphincter  see under muscle.

rectal sphincter  an incomplete band or thickening of the muscle fibers in the rectum a few inches above the anus in the upper part of the rectal ampulla.

tubal sphincter  an encircling band of muscle fibers at the junction of the uterine tube and the uterus.

vesical sphincter  internal sphincter muscle of urethra.

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anal sphincter

n.

Either of the two sphincter muscles of the anus. See under external and internal sphincter muscle of anus.

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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.

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sphincter [sfingk´ter]

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.

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anal

relating to the anus.

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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.

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.