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Each sphincter is associated with the lumen (opening) it surrounds. As long as the sphincter muscle is contracted, its length is shortened and the lumen is constricted (closed). Relaxation of the muscle causes it to lengthen, opening the lumen and allowing the passage of liquids, solids, or gases.
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that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the
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Functional sphincters do not have this localised muscle thickening and achieve their sphincteric action through muscle contraction around (extrinsic) or within (intrinsic) the structure.
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and other stomach contents from pushing up and into the oesophagus, but opens to let swallowed food pass into the stomach.
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Emanuel, Linda L.; Ferris, Frank D.; von Gunten, Charles F.; Hauser, Joshua M.; Von Roenn, Jamie H. (February 11, 2010).
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Anatomical sphincters have a localised and often circular muscle thickening to facilitate their action as a sphincter.
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Circular muscle that normally maintains constriction of a natural body passage or orifice
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Sphincters can be further classified into functional and anatomical sphincters:
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The lower esophageal sphincter, or cardiac sphincter, at the upper portion
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sphincter (or cardiac sphincter), which resides at the top of the
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Sphincters can also be voluntarily or involuntarily controlled:
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Many sphincters are used every day in the normal course of
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Vander, Arthur; Sherman, James; Luciano, Dorothy (1994).
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contents of the stomach from moving upward into the
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394:Human Physiology: The Mechanism of Body Function
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183:Involuntary sphincters are stimulated by
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240:upper oesophageal sphincters
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357:function to control the
229:orbicularis oculi muscle
355:precapillary sphincters
340:external anal sphincter
336:internal anal sphincter
277:at the junction of the
100:precapillary sphincters
231:, a muscle around the
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102:. Sphincters relax at
365:in response to local
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334:from the body, the
275:ileocecal sphincter
216:, belonging to the
214:pupillary sphincter
317:urethral sphincter
313:sphincter urethrae
210:sphincter pupillae
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106:, often releasing
346:and the outer is
290:sphincter of Oddi
268:pyloric sphincter
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353:The microscopic
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344:involuntary
200:Diagram of
143:oesophageal
118:Functioning
27:Identifiers
374:References
96:human body
369:activity.
367:metabolic
363:capillary
348:voluntary
304:into the
261:esophagus
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139:digestion
128:blowholes
87:sphincter
22:Sphincter
445:Category
430:Medscape
306:duodenum
298:pancreas
192:Examples
326:At the
253:stomach
220:in the
147:stomach
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257:acidic
249:cardia
112:faeces
108:fluids
91:muscle
359:blood
332:feces
321:urine
315:, or
294:liver
212:, or
151:acids
104:death
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338:and
328:anus
311:The
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218:iris
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233:eye
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57:FMA
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