WordNet

make ones way by force; "He muscled his way into the office"
animal tissue consisting predominantly of contractile cells (同)muscular_tissue
one of the contractile organs of the body (同)musculus
authority or power or force (especially when used in a coercive way); "the senators used their muscle to get the party leader to resign"
describing a circle; moving in a circle; "the circular motion of the wheel" (同)rotary, orbitual
an advertisement (usually printed on a page or in a leaflet) intended for wide distribution; "he mailed the circular to all subscribers" (同)handbill, bill, broadside, broadsheet, flier, flyer, throwaway

PrepTutorEJDIC

〈U〉(動物体の組織としての)『筋肉』,筋(きん);〈C〉(体の各部を動かす)筋肉 / 〈U〉力,(特に)筋力,腕力 / 《俗に》(…に)強引に割り込む《+『in on』(『into, through』)+『名』》
『円形の』,丸い / 回転して動く / 循環的な,旋回する;回遊する / (公衆に配布する)案内状,広告ビラ
筋肉の,筋力のある / 力ずくの

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/06/07 05:25:18」(JST)

wiki en

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.^[2]

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 esophageal sphincter (or cardiac sphincter), which resides at the top of the stomach, keeps stomach acids and other stomach contents from pushing up and into the esophagus. 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

^ ^a ^b Vander, 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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5. 成人における便失禁：疫学および評価 fecal incontinence in adults etiology and evaluation

English Journal

Circular RNA WDR77 target FGF-2 to regulate vascular smooth muscle cells proliferation and migration by sponging miR-124.

Chen J1, Cui L2, Yuan J3, Zhang Y3, Sang H3.
Biochemical and biophysical research communications.Biochem Biophys Res Commun.2017 Dec 9;494(1-2):126-132. doi: 10.1016/j.bbrc.2017.10.068. Epub 2017 Oct 16.
PMID 29042195

Magnetic Resonance Signal Intensity Ratio Measurement Before Uterine Artery Embolization: Ability to Predict Fibroid Size Reduction.

Duvnjak S1,2, Ravn P3, Green A4, Andersen PE5,6.
Cardiovascular and interventional radiology.Cardiovasc Intervent Radiol.2017 Dec;40(12):1839-1844. doi: 10.1007/s00270-017-1721-2. Epub 2017 Jun 8.
PMID 28597064

Structural Destabilization of Tropomyosin Induced by the Cardiomyopathy-linked Mutation R21H.

Ly T1, Krieger I2, Tolkatchev D1, Krone C1, Moural T3, Samatey FA4, Kang C3, Kostyukova AS1.
Protein science : a publication of the Protein Society.Protein Sci.2017 Nov 6. doi: 10.1002/pro.3341. [Epub ahead of print]
PMID 29105867

Japanese Journal

Developmental morphological changes in protrusions in Artemia intestinal circular muscles

Ueno Masaki,Kimura Taketoshi
Crustacean research (43), 25-30, 2014-12-15
… This study describes the electron microscopic features of protrusions on the intestinal circular muscle surface of Artemia nauplius larvae and adults. … The budding form of the protrusion from the circular muscle surface was observed, and junctions were detected both at the parts in contact among the protrusions and the connection between the protrusion and the circular muscle cell. …
NAID 110009878446

Role of various kinases in muscarinic M3 receptor-mediated contraction of longitudinal muscle of rat colon

Anderson Jr. Charles D.,Kendig Derek M.,Al-Qudah Mohammad,Mahavadi Sunila,Murthy Karnam S.,Grider John R.
Journal of Smooth Muscle
… The longitudinal muscle layer in gut is the functional opponent to the circular muscle layer during peristalsis. … The contractile activity of the longitudinal muscle is largely mediated by cholinergic neural input from myenteric plexus. … Phosphorylation of myosin light chain (MLC20) by MLC kinase (MLCK) is a prerequisite for contraction in both circular and longitudinal muscle cells. …
NAID 130005065375

飼料パーム油と中鎖脂肪酸トリグリセリドがニホンナマズ <I>Silurus asotus</I> 稚魚の成長と脂肪酸組成に及ぼす影響

Roslianah Asdari, Amal Biswas,山本慎一 [他],荒木秀雄,川島健, Roshada Hashim,滝井健二
水産増殖 62(1), 45-54, 2014
カゼインを含む半精製飼料に魚油（FO， PO および 8PO：2MCT 混合油を10%ずつ配合し，等脂質，窒素およびエネルギー含量の FO， PO および MCT 飼料を調製した。100<I> l</I> 容円型黒色水槽に平均体重7.3 g の稚魚を20尾ずつ収容して各試験区を設け，所定の飼料を 1 日 2 回飽食給与して8週間飼育した。なお，試験区は各飼料につき …
NAID 130005062544