Look up sphincter in Wiktionary, the free dictionary.
A sphincter is a circular muscle 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 human body, some microscopically small, in particular the millions of precapillary sphincters.[1] Sphincters relax at death, often releasing fluids and fæces.[2]
Contents
1Functions
2Classifications
3Examples
4References
Functions
Sphincters control the passage of liquids and solids. This is evident, for example, in the blowholes of numerous marine mammals.
Many sphincters are used every day in the normal course of digestion. For example, the lower oesophageal sphincter (or cardiac sphincter), which resides at the top of the stomach, keep stomach acids and other stomach contents from pushing up and into the oesophagus. During contraction of sphincter/circular muscles, the lumen (opening) associated with the sphincter constricts (closes). This constriction is caused by the shortening of the sphincter muscle. Relaxation of a sphincter muscle causes it to lengthen, opening the lumen.
Classifications
Sphincters can be further classified into functional and anatomical sphincters:
Anatomical sphincters have a localised and often circular muscle thickening to facilitate their action as a sphincter.
Functional sphincters do not have this localised muscle thickening and achieve their sphincteric action through muscle contraction around (extrinsic) or within (intrinsic) the structure.
Sphincters can also be voluntarily or involuntarily controlled:
Voluntary sphincters are supplied by somatic nerves.
Involuntary sphincters are stimulated by autonomic nerves.
Examples
Diagram of Ileocaecal valve and sphincter
The sphincter pupillae, or pupillary sphincter, belonging to the iris in the eye.
The orbicularis oculi muscle, a muscle around the eye.
The upper and lower oesophageal sphincters.
The lower sphincter, or cardiac sphincter, at the upper portion (cardia) of the stomach. This sphincter prevents the acidic contents of the stomach from moving upward into the esophagus.
The pyloric sphincter, at the lower end of the stomach.
The ileocecal sphincter at the junction of the small intestine (ileum) and the large intestine, which functions to limit the reflux of colonic contents back into the ileum.
The sphincter of Oddi, or Glisson's sphincter, controlling secretions from the liver, pancreas and gall bladder into the duodenum.
The sphincter urethrae, or urethral sphincter, controlling the exit of urine from the body.
At the anus, there are two sphincters which control the exit of feces from the body (see internal anal sphincter and external anal sphincter). The inner sphincter is involuntary and the outer is voluntary.
The microscopic precapillary sphincters function to control the blood flow into each capillary in response to local metabolic activity.[1]
The preputial sphincter, belonging to the human foreskin.
References
^ abVander, Arthur; Sherman, James; Luciano, Dorothy (1994). Human Physiology: The Mechanism of Body Function (Sixth Edition, International Edition). McGraw Hill, Inc. pp. 437–440. ISBN 0-07-113761-0.
^"Medscape Log In".
UpToDate Contents
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English Journal
Acute lumbosacral nerve stimulation does not affect anorectal motor function in a rodent model.
Devane LA1, Evers J1, Scott MS2, Knowles CH2, O'Connell P1,3, Jones JF1.
Neurogastroenterology and motility : the official journal of the European Gastrointestinal Motility Society.Neurogastroenterol Motil.2016 Mar;28(3):358-63. doi: 10.1111/nmo.12733. Epub 2015 Nov 26.
BACKGROUND: Sacral nerve stimulation has become a first line treatment for fecal incontinence, however, its effect on the motor function of the anorectum is uncertain. The aim of this study was to apply acute lumbosacral nerve stimulation in an animal model and to determine its effect on the externa
The effect of Flos Lonicerae Japonicae extract on gastro-intestinal motility function.
Nam Y1, Lee JM2, Wang Y3, Ha HS4, Sohn UD5.
Journal of ethnopharmacology.J Ethnopharmacol.2016 Feb 17;179:280-90. doi: 10.1016/j.jep.2015.12.056. Epub 2015 Dec 29.
ETHNOPHARMACOLOGICAL RELEVANCE: Flos Lonicerae Japonicae is a well-known herb of traditional Chinese medicine that has been used for heat-clearing, detoxification, anti-inflammation, throat pain and gastro-intestinal (GI) disorder. In order to verify the effect of Flos Lonicerae Japonicae on GI diso
The Annals of otology, rhinology, and laryngology.Ann Otol Rhinol Laryngol.2016 Feb 11. pii: 0003489416629978. [Epub ahead of print]
INTRODUCTION: Understanding of swallowing pressures after total laryngectomy (TL) and what constitutes a "functional" swallow are limited. Mobile structures are altered or removed after TL, with consequent effects on pressure profiles. High-resolution manometry (HRM) can characterize these pressures
… This classification was based on several traditional morphological features such as mesenterial arrangement, basal disc, acontium, and sphinctermuscle. …
The Tohoku Journal of Experimental Medicine 247(1), 41-49, 2019
… <p>Esophageal achalasia is a disease characterized by the impaired esophageal peristalsis and non-relaxation of the lower esophageal sphinctermuscle with unknown causes. …
sphincter /sphinc·ter/ (sfingk´ter) [L.] a ringlike muscle which closes a natural orifice or passage.sphinc´teralsphincter´ic anal sphincter , sphincter a´ni sphincter muscle of anus (external or internal). cardiac sphincter , cardioesophageal sphincter ...
A sphincter muscle is one that encircles the passages and openings of the body. Involved in many bodily functions, sphincter... ... 10 most extreme places on Earth Top 10 amazing movie makeup transformations Can ...