Birth Definitions

Anus Definition


The anus is a short, tubular structure that serves as the exit for the gastrointestinal tract. It is located at the junction of the rectum and the sigmoid colon. It is a muscular tube about 20 cm long and 2.5 cm in diameter, lined with mucous membrane. The mucous membrane is covered with epithelium, which is continuous with the lining of the anal canal. The main function of the anus is to allow for the expulsion of feces.

The word “anus” comes from the Latin word for “ring,” which describes its shape. The anus is surrounded by two sphincter muscles: the internal anal sphincter and the external anal sphincter. The main function of the anus is to control the expulsion of feces from the body. The anal sphincters are two muscles that surround the opening of the anus. These muscles control the release of feces. The internal anal sphincter is controlled by the autonomic nervous system, while the external anal sphincter is under voluntary control.

Significance in Childbirth and After

During labor and childbirth, the anus acts as a birth canal for babies. When a woman is giving birth vaginally, her baby’s head presses down on her rectum, causing it to bulge out slightly. This pressure forces the baby’s head to move through her birth canal and into the world. During this process there is a risk of tearing or other injury to the mother’s perineum (the area between the vagina and rectum), although this can be avoided by waiting for the body to naturally expel the baby, or by perineum massage.

Once the baby is born, the anus of the baby needs to be checked to find out if the baby does not have a condition known as imperforate anus. This condition is characterized by the absence of an anal opening, an anal opening that is in the wrong place, stool passing through places other than the anus, a swollen abdomen, or a fistula between the baby’s rectum and their reproductive system or urinary tract. 

Other Related Terms

There are a few terms that are closely associated with anus: 

  • Perineum: The area between the vagina and rectum where most vaginal deliveries occur. 
  • Anal sphincter: A ring of muscle that surrounds and controls the opening of the anus.
  • Meconium: A black, tarry substance that is present in the intestines of newborns.

This image shows how often the term ‘Anus’ is used in relation to other, similar birth terms:

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