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Diagram of the Anus

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Updated: September 14, 2006

The anus is the end of the line for the alimentary canal. During defecation, waste passes from the rectum, through the anal canal, and out through the anus.
Diagram of the Anus, © Donna Myers 2006 (coloncancer.guide@about.com)

Anus

© Donna Myers 2006
To put it bluntly, the anus is the hole poop passes through on its way out of the body. Entry and exit are regulated by muscles called external and internal sphincters.

The external anal sphincter keeps the exit closed throughout the day. If you've ever made a conscious effort to close the flood gates during a bout of diarrhea, the external anal sphincter is the muscle you were controlling.

The internal anal sphincter is an involuntary muscle, which means it does its job on its own without any orders from you. What is its job? The internal anal sphincter helps keep poop from leaving the body before its time and also helps escort it out when the time is right.
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