Sphincter
Sphincter
Circular muscle that normally maintains constriction of a natural body passage or orifice
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,[citation needed] some microscopically small, in particular the millions of precapillary sphincters.[1] Sphincters relax at death, often releasing fluids and faeces.[2]