- sphincter
- A muscle that encircles a duct, tube, or orifice in such a way that its contraction constricts the lumen or orifice. SYN: musculus s. [TA], s. muscle [TA]. [G. sphinkter, a band or lace]- anatomic s. an accumulation of muscular circular fibers or specially arranged oblique fibers the function of which is to reduce partially or totally the lumen of a tube, the orifice of an organ, or the cavity of a viscus; the closing component of a pylorus.- s. angularis, angular s. thickening of the circular muscular layer forming a proposed intermediate s. at the level of the angular notch of the stomach. While the thickening of the circular muscle may indicate the commencement of the pyloric antrum, true functional sphincteric activity distinct from the other peristaltic contractions of the stomach is not observed although some of these may in fact temporarily close off the antrum from the remainder of the stomach lumen. SYN: antral s., midgastric transverse s., s. antri, s. intermedius, s. of antrum, s. of gastric antrum.- s. ani tertius the third s. of the anorectum, a physiological s. at the sigmoidorectal junction.- s. antri SYN: s. angularis.- anular s. a short thickening of circular muscular fibers, similar to a ring; a ring-shaped s. as opposed to a segmental s..- artificial s. a s. produced by surgical procedures to reduce speed of flow in the digestive system or to maintain continence of the intestine.- basal s. the thickening of the circular muscular coat at the base of the ileal papilla at the terminal ileum. SYN: sphincteroid tract of ileum.- bicanalicular s. a s. encircling two canals, such as the terminal portions of the common bile duct and the main pancreatic duct.- canalicular s. a s. located somewhere along the course of an organ, a tube, or a duct, as opposed to ostial s..- s. of (common) bile duct [TA] smooth muscle s. of the common bile duct immediately proximal to the hepatopancreatic ampulla and organized into a superior and inferior s.; it is this s. that controls the flow of bile in the duodenum. SYN: musculus s. ductus choledochi [TA], musculus s. ductus biliaris, Boyden s., choledochal s., s. muscle of common bile duct.- external anal s. [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. SYN: musculus s. ani externus [TA], external s. muscle of anus.- external urethral s. [TA] muscle that constricts membranous urethra to retain urine in bladder; nerve supply, pudendal. SYN: s. urethrae externus [TA], Guthrie muscle, musculus constrictor urethrae, musculus s. urethrae externus, s. muscle of urethra, Wilson muscle (1).- external urethral s. of female [TA] composed of striated (voluntary) muscle and more properly a urogenital s., part forms a true anular s. around the urethra, part extends superiorly to the neck of the bladder, part passing anterior to the urethra that attaches to the ischial rami (compressor urethrae muscle) and a bandlike part that encircles both the urethra and the vagina (urethrovaginal s.). SYN: musculus s. urethrae externus femininae [TA].- external urethral s. of male [TA] composed of striated (voluntary) muscle, includes a tubelike portion that encircles the membranous urethra, but also has a large, troughlike portion that ascends the anterior aspect of the prostatic urethra to the neck of the bladder and a part that passes anteriorly to the membranous urethra and attaches to the ischial rami on each side (compressor urethrae muscle). SYN: musculus s. urethrae externus masculinae [TA].- first duodenal s. the s. supposedly located at the level of the aboral extremity of the duodenal bulb.- functional s. SYN: physiologic s..- s. of hepatopancreatic ampulla [TA] the smooth muscle s. of the hepatopancreatic ampulla within the duodenal papilla. SYN: musculus s. ampullae hepatopancreaticae [TA], musculus s. ampullae biliaropancreaticae, musculus s. ampullae, s. of ampulla, s. of biliaropancreatic ampulla, Glisson s., hepatopancreatic s., Oddi s..- Hyrtl s. a band, generally incomplete, of circular muscular fibers in the rectum about 10 cm above the anus (upper rectal ampulla).- ileal s. a thickening of circular musculature at the free margin of the ileal papilla. SYN: ileocecocolic s., marginal s., operculum ilei, Varolius s..- ileocecocolic s. SYN: ileal s..- iliopelvic s. SYN: midsigmoid s..- inferior esophageal s. a physiologic s. at the level of the esophagogastric junction; this is in fact an extrinsic s. formed by the surrounding musculature of the esophageal hiagus of the right crus of the diaphragm; causes a normally occurring constriction at the esophagogastric junction observable with a barium swallow. SYN: s. constrictor cardiae.- s. intermedius SYN: s. angularis.- internal anal s. [TA] a smooth muscle ring, formed by an increase of the circular fibers of the rectum, situated at the upper end of the anal canal, internal to the outer voluntary external anal s.. This s. is maximally contracted when the rectal ampulla is “at rest”—empty or relaxed to accommodate a distending fecal mass. It is inhibited with filling of the ampulla, increased distension, and peristalsis. SYN: musculus s. ani internus [TA], internal s. muscle of anus.- internal urethral s. [TA] the complete collar of smooth muscle cells of the neck of the urinary bladder that extends distally to surround the preprostatic portion of the male urethra. There is not comparable structure in the neck of the female bladder; the internal urethral s. may exist to prevent reflux of semen into the bladder. SYN: musculus s. urethrae internus, preprostatic s., supracollicular s., anulus urethralis, muscular s. supracollicularis, musculus s. vesicae, preprostate urethral s., proximal urethral s., s. muscle of urinary bladder, s. vesicae.- lower esophageal s. (LES) musculature of the gastroesophageal junction that is tonically active except during swallowing.- macroscopic s. a s. visible to the naked eye.- mediocolic s. a physiological s. located midway in the ascending colon.- microscopic s. a s. visible only under the microscope.- midgastric transverse s. SYN: s. angularis.- myovascular s. a s. having a muscular and a vascular (usually venous) component. See myovenous s..- myovenous s. a s. having a muscular and a venous component, e.g., at the pharyngoesophageal junction and anal canal.- Nélaton s. See transverse folds of rectum, under fold. SYN: Nélaton fibers.- O'Beirne s. SYN: rectosigmoid s..- s. oris SYN: orbicularis oris (muscle).- s. of pancreatic duct [TA] smooth muscle s. of the main pancreatic duct immediately proximal to the hepatoduodenal ampulla. SYN: musculus s. ductus pancreatici, pancreatic s., s. muscle of pancreatic duct.- pathologic s. a thickening of circular musculature caused by disease.- pelvirectal s. SYN: rectosigmoid s..- physiologic s. a section of a tubular structure that acts as if it has a band of circular muscle to constrict it, although no such specialized structure can be found on morphologic examination. SYN: functional s., radiologic s..- prepyloric s. a band of circular muscular fibers in the wall of the stomach near the gastroduodenal pylorus.- s. pupillae [TA] a ring of smooth muscle fibers surrounding the pupillary border of the iris. SYN: musculus s. pupillae [TA], s. muscle of pupil.- pyloric s. [TA] a thickening of the circular layer of the gastric musculature encircling the gastroduodenal junction. SYN: musculus s. pylori [TA], s. muscle of pylorus.- radiologic s. SYN: physiologic s..- rectosigmoid s. a circular band of muscular fibers at the rectosigmoid junction. SYN: O'Beirne s., O'Beirne valve, pelvirectal s..- smooth muscular s. SYN: lissosphincter.- striated muscular s. SYN: rhabdosphincter.- superior esophageal s. SYN: inferior constrictor (muscle) of pharynx. See inferior constrictor (muscle) of pharynx.- s. of third portion of duodenum a physiologic s. supposedly located at the horizontal (inferior) portion of the duodenum.- urethrovaginal s. [TA] voluntary, bandlike part of external urethral s. of female that encircles both urethra and vagina superior to the perineal membrane. SYN: musculus s. urethrovaginalis [TA].- s. vaginae SYN: bulbospongiosus (muscle).- Varolius s. SYN: ileal s..- s. vesicae biliaris the s. of the gallbladder, at the transition between the neck of the gallbladder and the cystic duct.
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sphinc·ter 'sfiŋ(k)-tər n an annular muscle surrounding and able to contract or close a bodily opening see anal sphincter, cardiac sphincter, precapillary sphincter, pyloric sphinctersphinc·ter·al -t(ə-)rəl adj* * *
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 opening between the stomach and duodenum (pyloric sphincter).* * *
sphinc·ter (sfingkґtər) [L., from Gr. sphinktēr that which binds tight] a ringlike band of muscle fibers that constricts a passage or closes a natural orifice; called also musculus sphincter [TA]. sphincteral, sphincteric adj
Medical dictionary. 2011.
