Friday, June 7, 2013

sphincter muscles

I got into an argument with someone last weekend about the number of sphincters in the human body. She (with a PhD in physical therapy who took anatomy) argued that there were only 4, I argued that there were a lot more and about 12 large/primary ones that she should know about.  

"sphincter is an anatomical structure, 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 50 types in the human body, some microscopically small, in particular the millions of precapillary sphincters."
Examples: 

The sphincter pupillae, or pupillary sphincter, belonging to the iris in the eye.
The orbicularis oculi muscle, a muscle around the eye.

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 oesophagus.
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 liverpancreas 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.

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