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sphincter

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sphincter

Anatomy a ring of muscle surrounding the opening of a hollow organ or body and contracting to close it
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

sphincter

[′sfiŋk·tər]
(anatomy)
A muscle that surrounds and functions to close an orifice.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Sphincter

 

a ringlike muscle that constricts to close a natural orifice such as the oral or anal opening, or to narrow the passage from one part of a hollow tubular organ to another, for example, from the stomach and bile duct to the duodenum and from the bladder to the urethra. The sphincter is always in a tonic state. The orbicular muscle of the iris is a sphincter. Some sphincters consist of striated muscle and others of smooth muscle innervated by the autonomic nervous system.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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References in periodicals archive
To keep the acidic stomach contents away from its delicate tissue, the esophagus relies only on gravity and a sphincter muscle at the lower end.
In patients with dyssynergic defecation and loss of stool, the goal of neuromuscular training is two-fold: 1) to correct the dyssynergia or incoordination of the abdominal, rectal, puborectalis, and anal sphincter muscles to achieve a normal and complete evacuation; and 2) to enhance rectal sensory perception in patients with impaired rectal sensation (Markland et al., 2008).
Proper management would have enabled diagnosis of the cancer at a stage when radical surgery could have been avoided and the sphincter muscle preserved, eliminating the need for a permanent colostomy.
Most incontinence in women is triggered by problems with the bladder and sphincter muscles, which can weaken with age.
Nevertheless they were able to induce regeneration of the mouse's own urethral sphincter muscle."
These include loss of muscle tone of the sphincter muscle of the oesophagus, hairball obstruction, intestinal parasites, gastric ulcers, etc.
Interventions to reduce sphincter tone include Botox injections, surgical incision of the sphincter muscle or a urethral stent to keep the sphincter open.
"A person must be able to squeeze the sphincter muscle to prevent urine from leaking out and the detrusor muscle must stay relaxed so that the bladder can expand.
Normal urination requires the proper function of the urinary sphincter muscle (which controls the flow of urine out of the body) and the detrusor muscle in the bladder wall.
Genital tract trauma is one of the most common obstetric morbidity after vaginal delivery.1 Long term perineal morbidity is associated with failure to rec-ognize or to repair perineal tears adequately, as well as trauma to the external anal sphincter can lead to major physical, psychological and social problems.2 There is a wide variety in the reported incidence of anal sphincter muscle injury from childbirth, with the true incidence likely to be approximately 11% of postpartum women.3 As far as risk factors are con-cerned both mother and fetus are being blamed for it.
When the stool is too soft, the sphincter muscle doesn't apply enough pressure to empty the sacs as the dog expels feces.
In addition, certain foods and drinks--chocolate; tomatoes; raw onions; garlic; black pepper; vinegar; peppermint; fatty or spicy foods, and caffeinated, carbonated, or alcoholic beverages--relax the sphincter muscle, making reflux more likely.
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