SPHINCTER

A 'sphincter' is a structure, usually a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. There are over 40 different sphincters in the human body; some of these sphincters are microscopic in size.

Contents

Categories of Sphincter

Examples of sphincters

Categories of Sphincter

★ Anatomical Sphincters:

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★ Type one: A thickening of a smooth muscle that functions as a sphincter, for instance: internal Anal Sphincter.

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★ Type two: A specific skeletal muscle that functions as a sphincter, for instance: External Anal Sphincter.

★ Physiological Sphincters:

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★ A structure that controls an internal passage but is not anatomical, for instance: Cardia/lower esophageal Sphincter.

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★ The Sphincter is basically the hole that cuts off your poo.

Examples of sphincters

★ The ''sphincter pupillae'', or pupillary sphincter, belonging to the iris in the eye.

★ The orbicularis oris muscle, a muscle around the mouth.

★ The upper esophageal sphincter

★ The cardia/lower esophageal sphincter, or cardiac sphincter at the upper portion 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, which prevents the backup of non-digested material into the small intestine.

★ 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 voluntary.
Sphincters prove effective in the mediation of the entrance or release of liquids and fluids; this is evident in the blowholes of numerous marine mammals, for example.