sphincter

n.
A ringlike muscle that normally maintains constriction of a body passage or orifice and that relaxes as required by normal physiological functioning.

[Late Latin sphinctēr, from Greek sphinktēr, from sphingein, to bind tight.]

sphincteral sphinc'ter·al adj.

A band of muscle encircling one of the body's ‘tubes’, and so able to alter the ‘bore’ by contracting/relaxing. In the alimentary tract there are sphincters at the exit from the stomach, between the small and large intestine, and at the anus; another regulates the flow of bile and pancreatic juice into the duodenum. In the urogenital tract, there are sphincters at the exit from the bladder. They occur also in the walls of small arterial blood vessels, regulating the flow into the capillaries beyond, according to local requirements. Those which assist retention of the excreta are partly under voluntary control; all the others, formed only of smooth muscle, are regulated by the autonomic nervous system; in general, sympathetic nerves constrict them; in the gut, parasympathetic nerves relax them. The thin sheet of circular muscle of the iris which constricts the pupil of the eye is also known as a sphincter — it is stimulated by parasympathetic nerves, in response to light and as part of accommodation for near vision.

— Stuart Judge

See alimentary system; autonomic nervous system; bladder.

n

A circular band of muscle fibers that constricts a passage or closes a natural opening in the body.

A circular muscle the contraction of which can close an opening. Sphincter muscles in blood vessels play an important role in shunting blood from one part of the body to another.

A circular muscle that constricts a passage or closes a natural orifice. When relaxed, a sphincter allows materials to pass through the opening. When contracted, it closes the opening. The principal abnormalities relate to function. Failure to open may be because of spasm or achalasia, due usually to failure of parasympathetic nerve supply. Failure to close usually due to absence of sympathetic nerve supply. The important sphincters are the anal, ileal, pharyngoesophageal, pupillary, pyloric, reticulo-omasal, teat, urethral, vaginal and vesical.

• cardiac s. — the functional sphincter at the gastric end of the esophagus.
• s. control — is by the autonomic nervous system.
• esophageal s. — see cardiac sphincter.
• s. of Oddi — bile duct sphincter.
• pupillary s. — a ring of smooth muscle around the pupillary border of the iris.

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Dansk (Danish)
n. - ringmuskel, lukkemuskel

Nederlands (Dutch)
sluitspier

Français (French)
n. - sphincter

Deutsch (German)
n. - Schließmuskel

Ελληνική (Greek)
n. - (ανατ.) σφιγκτήρας (μυς)

Italiano (Italian)
sfintere

Português (Portuguese)
n. - esfíncter (m)

Русский (Russian)
сфинктер, сжиматель

Español (Spanish)
n. - esfínter

Svenska (Swedish)
n. - ringmuskel, sfinkter, slutmuskel

中文（简体）(Chinese (Simplified))
括约肌

中文（繁體）(Chinese (Traditional))
n. - 括約肌

한국어 (Korean)
n. - 괄약근, 늘옴치근

日本語 (Japanese)
n. - 括約筋

العربيه (Arabic)
‏(الاسم) عضله عاصرة‏

עברית (Hebrew)
n. - ‮(שריר) טבעתי, סוגר, פי הטבעת‬

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