sphincter

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 It might be outdated or ideologically biased.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.