Dominic Stone
The anus, or butthole, is the external opening of the rectum, located inside the intergluteal cleft. It is the final part of the gastrointestinal tract, where food waste completes its journey through the digestive tract and exits the body. The anus is surrounded by two muscular rings, the internal and external anal sphincters, which control the release of stool. These muscles work together with nerves and mucous membranes to facilitate healthy bowel movements that can be controlled.
| Characteristics | Values |
|---|---|
| Definition | The anus is the external opening of the rectum located inside the intergluteal cleft. |
| Function | The primary function of the anus is to control the exit of feces from the body during an act of defecation. It also functions as a sexual organ and an intake orifice for treatment (e.g., suppository, edema). |
| Structure | The anus is surrounded by two muscular rings, the internal and external anal sphincters, which control defecation. |
| Innervation | The anal sphincters are innervated by the pudendal nerve, which sends signals to control the closure of the sphincters and prevent stool leakage. |
| Blood Supply | The anus receives blood from the inferior rectal artery. |
| Tissue | The anus is lined with mucous membranes and the tissue changes from mucosa to normal skin at the pectinate line. |
| Sensitivity | The anus is highly sensitive to pain and other sensations, especially in the lower two-thirds below the pectinate line. |
| Common Conditions | Common conditions affecting the anus include hemorrhoids, fissures, infections, and in some cases, cancer. |
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What You'll Learn
The anus is a muscle and an organ
The anus is the final part of the gastrointestinal tract, and it is located at the end of the large intestine. It is the external opening of the rectum, which is the last few inches of the large intestine. The anus has several functions, including eliminating waste, acting as a sexual organ, and serving as an intake orifice for treatments such as suppositories.
The anus is surrounded by two muscular rings, the internal and external anal sphincters, which control defecation. These sphincters are circular muscles that maintain constriction of the orifice and relax as needed during normal physiological functions, such as passing stool. The internal sphincter is involuntary, relaxing in response to intra-rectal pressure, while the external sphincter is under voluntary control. Together, these muscles work to control the release of stool and maintain continence.
In addition to the sphincter muscles, other muscles also play a role in the anus's function. For example, the puborectalis muscle creates an angle in the rectum, helping to keep stool in until defecation. During a bowel movement, muscles in the abdominal wall contract, increasing pressure in the rectum and aiding in pushing stool out. Pelvic floor muscles are also involved in the process, working with the anal sphincter to control the expulsion of stool.
While the anus is indeed a muscle, it is also considered an organ. As the final part of the gastrointestinal tract, it plays a crucial role in eliminating waste from the body. The anus has a complex structure, with various parts working together to facilitate bowel movements and protect the body from infections. The muscles, nerves, and mucous membranes in the anus coordinate to enable healthy and controlled defecation.
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The internal anal sphincter is involuntary
The anus is the final part of the gastrointestinal tract and is the external opening of the rectum. The anal sphincter is a group of muscles at the end of the rectum that surrounds the anus and controls the release of stool. There are two types of anal sphincters: the internal anal sphincter and the external anal sphincter. The internal anal sphincter is involuntary, while the external anal sphincter is under voluntary control.
The internal anal sphincter is a specialised thickened portion of the inner circular layer of smooth muscle of the large intestine. It extends from the pectinate line (anorectal junction) proximally to just proximal to the anal orifice distally. Its muscle fibres are arranged in a spiral manner. The internal anal sphincter is contracted in its resting state but reflexively relaxes in certain contexts, most notably during defecation.
The defecation cycle begins with the recto-anal inhibitory reflex (RAIR), where the internal anal sphincter relaxes. This allows a small amount of rectal contents to descend into the anal canal, where specialised mucosa samples whether it is gas, liquid, or solid. The internal anal sphincter also relaxes in response to intra-rectal pressure, which is caused by the rectum filling with faeces and pushing against the walls of the anal canal. This relaxation of the internal anal sphincter allows faeces to enter the canal.
The internal and external anal sphincters work together to produce a bowel movement. When stool moves through the digestive tract, it triggers the internal anal sphincter to relax, which in turn makes the external anal sphincter contract. This response is called the defecation reflex. The internal anal sphincter contributes 55% of the resting pressure of the anal canal and is crucial for bowel continence, especially for liquids and gases.
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The external anal sphincter is voluntary
The human anus is the external opening of the rectum, located inside the intergluteal cleft. The anal sphincter is a group of muscles at the end of the rectum, which surrounds the anus and controls the release of stool. There are two muscles that make up the anal sphincter: the internal anal sphincter and the external anal sphincter.
The anal sphincter reflex is a process that occurs when stool moves through the digestive tract, triggering the internal anal sphincter to relax and the external anal sphincter to contract. This response is called the defecation reflex. If there is a loss of muscle control in the sphincter muscles, faecal incontinence may occur.
Several diseases, conditions, and injuries can affect the external anal sphincter. For example, anismus is a functional disorder of the pelvic floor muscles, including the external anal sphincter, caused by a problem with the way these muscles contract and relax during defecation. Anal fissures are tears in the lining of the anus that often extend into the internal anal sphincter. They are caused by overstretching the anal canal, which can occur when passing a very hard or large bowel movement.
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Pelvic floor muscles and anal sex
The anus is the external opening of the rectum, located inside the intergluteal cleft. The anal sphincter is a group of muscles at the end of the rectum that surrounds the anus and controls the release of stool. There are two types of anal sphincters: internal and external. The internal sphincter is involuntary, while the external sphincter is voluntary. These muscles are essential for maintaining continence and controlling defecation.
The pelvic floor muscles are a group of muscles that support the bladder, bowel, and uterus. They stretch from the pubic bone in the front of the body to the tailbone (coccyx) in the back. These muscles also wrap around the openings of the vagina, anus, and urethra. The pelvic floor muscles help with essential bodily functions, including stabilising the core, assisting with urination, defecation, and sexual function.
When it comes to anal sex, the pelvic floor muscles play a crucial role in both men and women. In men, strong pelvic floor muscles are important for erectile function and ejaculation. In women, voluntary contractions of the pelvic floor muscles contribute to sexual sensation and arousal. Additionally, strong pelvic floor muscles in women can help prevent pelvic organ prolapse, which is a condition where the pelvic organs, such as the uterus, rectum, and bladder, bulge into the vagina or protrude from its opening. This condition is more common after menopause.
To maintain healthy pelvic floor muscles, it is important to exercise them regularly. Kegel exercises, for example, can help strengthen these muscles and improve muscle control. It is important to ensure that you are exercising the correct muscles when performing Kegels. Consulting a healthcare provider or a physical therapist can provide guidance on properly contracting and relaxing the pelvic floor muscles.
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Conditions and injuries of the anal sphincter
The anal sphincter is a group of muscles at the end of the rectum, which is located at the last few inches of the large intestine. The anal sphincter surrounds the anus and controls the release of stool, thereby maintaining continence. There are two muscles: the internal anal sphincter and the external anal sphincter.
Several diseases, conditions, and injuries can affect the anal sphincter. Anal fissures, for example, are tears in the lining of the anus that often extend into the internal anal sphincter. They are caused by overstretching the anal canal, which can occur when passing a very hard or large bowel movement. Symptoms of an anal fissure include pain and/or a sensation of tearing during a bowel movement, and there may be bright red blood in the toilet or on the toilet paper. Anal fissures may be treated with topical medications, medications that help relax the sphincter muscle, or surgery.
Another condition that can affect the anal sphincter is anismus, a functional disorder of the pelvic floor muscles, including the external anal sphincter. It is caused by a problem with the way these muscles contract and relax during defecation. Anismus is often treated with pelvic floor exercises and injections of botulinum toxin (Botox).
Sphincter injuries refer to tears or damage to the muscle that surrounds the anal canal, which can result in a decreased ability to control bowel movements and contribute to symptoms of accidental bowel leakage. These injuries can occur as a result of anal or rectal surgery, obstetrical trauma, or other trauma to the rectum. Treatment options for sphincter injuries include surgical repair of the anal sphincter muscle and biofeedback therapy, a treatment used to help strengthen the muscles of the anus and pelvic floor to decrease incidents of accidental bowel leakage.
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Frequently asked questions
The butthole, or anus, is the external opening of the rectum located inside the intergluteal cleft. It is the final part of the gastrointestinal tract.
The anus is surrounded by muscles, nerves, and mucous membranes. Two muscular rings, the internal and external anal sphincters, control the release of stool. The external sphincter is a skeletal muscle that can be controlled consciously, while the internal sphincter is a smooth muscle that is not under voluntary control.
The primary function of the butthole is to control the exit of feces from the body during defecation. Muscles, nerves, and mucous membranes in the anus work together to facilitate healthy bowel movements that can be controlled.
