Table of ContentsView AllTable of ContentsAnatomyFunctionConditions
Table of ContentsView All
View All
Table of Contents
Anatomy
Function
Conditions
The anal sphincter muscles may be damaged if you have trouble holding in stool and/or urine (or it leaks out) or if you have pain in your rectum.
This article will go over the anatomy of the anal sphincter and its function. You will also learn about conditions that affect the anal sphincter and what happens if the anal sphincter is damaged.
Dorling Kindersley / Getty Images
Anatomy of Anal Sphincters
The rectum of an adult is, on average, about 4.7 inches long. The lower part of the rectum is the anal sphincter.
The anal sphincter consists of two muscles:
Thepudendal nerveis a major nerve in the pelvis. It tells the muscles that control pelvic organs and genitals to move.
One of the nerve’s jobs is to send messages to its branches that tell the anal sphincter to close and prevent stool and urine from leaking out. This is calledanal sphincter innervation.
The Pudendal Nerve and What it Does
Function of Anal Sphincters
Theanal sphincter reflexis a process that occurs when stool moving through the digestive tract triggers the internal anal sphincter to relax, which in turn makes the external anal sphincter contract. This response is also called the defecation reflex.
The internal anal sphincter and external anal sphincter work together to produce a bowel movement but in different ways.
If there is a loss of muscle control in the sphincter muscles,fecal incontinencemay occur.
Thin muscle
Keeps rectum closed when not ready for bowel movement; relaxes with adequate pressure
External Anal SphincterThick muscleCan be voluntarily clenched/unclenched (e.g., holding a bowel movement until you reach a restroom)Conscious activation allows stool to pass from the body
Thick muscle
Can be voluntarily clenched/unclenched (e.g., holding a bowel movement until you reach a restroom)
Conscious activation allows stool to pass from the body
Improving Tightening of Your Anal Sphincter
Diseases and Conditions
Several diseases, conditions, and injuries can affect the anal sphincter. Symptoms of these conditions can vary, but generally speaking, signs that you may have a problem with your anal sphincter can include:
Anal Stenosis
Anal stenosis is not a common condition, but it can be related toinflammatory bowel disease (IBD). It is more common in Crohn’s disease than in ulcerative colitis.
In anal stenosis, the internal anal sphincter becomes narrowed to the point where it is difficult to have a bowel movement. Other symptoms include pain and bleeding.
Anal stenosis can occur after surgery—especially hemorrhoid removal—or be associated with laxative overuse or infections.
This condition may be treated with stool softeners or fiber supplements. Surgery to correct the problem may also be necessary.
Anismus
Symptoms of anismus include:
Anismus is often treated with pelvic floor exercises. Injections of Botulinum toxin (Botox) can also help.
Anal Fissure
Symptoms of an anal fissure include pain and/or a sensation of tearing during a bowel movement. There may be bright red blood in the toilet or on the toilet paper. These symptoms usually occur with every bowel movement. Because the damage can be made worse with each bowel movement, it is not uncommon for the condition to become chronic.
Anal fissures may be treated with topical medications, medications that help relax the sphincter muscle, or surgery.
Anorectal Malformation
An anorectal malformation is a condition that occurs in around 1 out of every 5,000 births. This birth defect causes the anus to develop abnormally.
Anorectal malformations can be mild to severe and can affect the sphincter and/or other parts of the rectum and anus. Surgery is required to correct them.
Anal Crohn’s Disease
Because Crohn’s disease can affect any part of the digestive tract from the mouth to the anus, it can also affect the anal sphincter. It’s estimated that as many as one-third of patients with Crohn’s disease will have complications in theperianal area(the part of the body around the anus).
People with Crohn’s disease may develop problems in the anal sphincter, including:
Anal Crohn’s disease can be managed in a few different ways depending on the symptoms and complications. In many cases, antibiotics are prescribed to treat infection, and surgery is sometimes also necessary.
Hemorrhoids (Piles)
Ahemorrhoidis a vein around the anus that becomes swollen. Almost anyone can develop hemorrhoids, and they are a particular problem for older adults, people who are pregnant, and people who have chronic diarrhea or constipation.
Hemorrhoids can be internal or external. Internal hemorrhoids are above the internal anal sphincter. External hemorrhoids are below the external anal sphincter.
Sometimes, the internal anal sphincter traps hemorrhoids. This condition is called strangulated hemorrhoids and can be very painful.
Hemorrhoids can usually be managed at home with topical medication and regular sitz baths. Surgery is often the best way to correct a strangulated hemorrhoid.
Fecal Incontinence
Some people with IBD have incontinence—the involuntary release of stool from the rectum.This can happen because of a flare-up of the disease or damage to the muscles of the anal sphincter.
Fecal incontinence can be very distressing, and getting the inflammation from IBD under control is important to prevent it.
A damaged anal sphincter might need to be fixed with surgery. Sometimes, a surgeon can just tighten the sphincter to fix the problem.In other cases, a surgery called an analsphincterotomycan be done to remove the sphincter.
The amount of time this repair might last depends on how well surgery goes and whether there are any complications. One study found that anal sphincter repairs to help prevent fecal incontinence were still helping patients at least three years after they had the procedure.
How to Treat Fecal Incontinence From IBD
Summary
The anal sphincter is a pair of muscles at the end of the rectum that controls the release of stool. When these muscles become damaged, you may have difficulty controlling your bowel movements.
Several conditions can affect the anal sphincter muscles, including anal fissure, anal Crohn’s disease, hemorrhoids, fecal incontinence, and others. These conditions range from mild to severe. Some can be corrected with home care while others require surgery.
13 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Keef KD, Co CA.Control of motility in the internal anal sphincter.J Neurogastroenterol Motil. 2019;25(2):189-204. doi:10.5056/jnm18172Chiarelli M, Guttadauro A, Maternini M, et al.The clinical and therapeutic approach to anal stenosis.Ann Ital Chir.2018;89:237-241.Pisano U, Irvine L, Szczachor J, Jawad A, MacLeod A, Lim M.Anismus, physiology, radiology: Is it time for some pragmatism? A comparative study of radiological and anorectal physiology findings in patients with anismus.Ann Coloproctol. 2016;32(5):170-174. doi:10.3393/ac.2016.32.5.170Johns Hopkins Medicine.Anal fissures.Wood RJ, Levitt MA.Anorectal malformations.Clin Colon Rectal Surg. 2018;31(2):61-70. doi:10.1055/s-0037-1609020Kelley KA, Kaur T, Tsikitis VL.Perianal Crohn’s disease: challenges and solutions.Clin Exp Gastroenterol.2017;10:39-46. doi:10.2147/CEG.S108513Vogel JD, Johnson EK, Morris AM, et al.Clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula.Dis Colon Rectum. 2016;59(12):1117-1133. doi:10.1097/DCR.0000000000000733Johns Hopkins Medicine.Hemorrhoids.Davis BR, Lee-Kong SA, Migaly J, Feingold DL, Steele SR.The American Society of Colon and Rectal Surgeons clinical practice guidelines for the management of hemorrhoids.Dis Colon Rectum. 2018;61(3):284-292. doi:10.1097/DCR.0000000000001030Barros LL, Farias AQ, Rezaie A.Gastrointestinal motility and absorptive disorders in patients with inflammatory bowel diseases: Prevalence, diagnosis and treatment.World J Gastroenterol.2019;25(31):4414-4426. doi:10.3748/wjg.v25.i31.4414North Carolina Surgery UNC Health Care.Anal sphincter repair.Lu Y, Lin A.Lateral Internal Sphincterotomy.JAMA. 2021;325(7):702. doi:10.1001/jama.2020.16708Berg MR, Gregussen H, Sahlin Y.Long-term outcome of sphincteroplasty with separate suturing of the internal and the external anal sphincter.Tech Coloproctol. 2019;23(12):1163-1172. doi:10.1007/s10151-019-02122-7Additional ReadingBrisinda G, Vanella S, Cadeddu F, et al.Surgical treatment of anal stenosis.World J Gastroenterol. 2009;15(16):1921-1928. doi:10.3748/wjg.15.1921Lewis RT, Maron DJ.Anorectal Crohn’s disease.Surg Clin North Am. 2010 Feb;90(1):83-97, Table of Contents. doi:10.1016/j.suc.2009.09.004MedlinePlus.Hemorrhoids.
13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Keef KD, Co CA.Control of motility in the internal anal sphincter.J Neurogastroenterol Motil. 2019;25(2):189-204. doi:10.5056/jnm18172Chiarelli M, Guttadauro A, Maternini M, et al.The clinical and therapeutic approach to anal stenosis.Ann Ital Chir.2018;89:237-241.Pisano U, Irvine L, Szczachor J, Jawad A, MacLeod A, Lim M.Anismus, physiology, radiology: Is it time for some pragmatism? A comparative study of radiological and anorectal physiology findings in patients with anismus.Ann Coloproctol. 2016;32(5):170-174. doi:10.3393/ac.2016.32.5.170Johns Hopkins Medicine.Anal fissures.Wood RJ, Levitt MA.Anorectal malformations.Clin Colon Rectal Surg. 2018;31(2):61-70. doi:10.1055/s-0037-1609020Kelley KA, Kaur T, Tsikitis VL.Perianal Crohn’s disease: challenges and solutions.Clin Exp Gastroenterol.2017;10:39-46. doi:10.2147/CEG.S108513Vogel JD, Johnson EK, Morris AM, et al.Clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula.Dis Colon Rectum. 2016;59(12):1117-1133. doi:10.1097/DCR.0000000000000733Johns Hopkins Medicine.Hemorrhoids.Davis BR, Lee-Kong SA, Migaly J, Feingold DL, Steele SR.The American Society of Colon and Rectal Surgeons clinical practice guidelines for the management of hemorrhoids.Dis Colon Rectum. 2018;61(3):284-292. doi:10.1097/DCR.0000000000001030Barros LL, Farias AQ, Rezaie A.Gastrointestinal motility and absorptive disorders in patients with inflammatory bowel diseases: Prevalence, diagnosis and treatment.World J Gastroenterol.2019;25(31):4414-4426. doi:10.3748/wjg.v25.i31.4414North Carolina Surgery UNC Health Care.Anal sphincter repair.Lu Y, Lin A.Lateral Internal Sphincterotomy.JAMA. 2021;325(7):702. doi:10.1001/jama.2020.16708Berg MR, Gregussen H, Sahlin Y.Long-term outcome of sphincteroplasty with separate suturing of the internal and the external anal sphincter.Tech Coloproctol. 2019;23(12):1163-1172. doi:10.1007/s10151-019-02122-7Additional ReadingBrisinda G, Vanella S, Cadeddu F, et al.Surgical treatment of anal stenosis.World J Gastroenterol. 2009;15(16):1921-1928. doi:10.3748/wjg.15.1921Lewis RT, Maron DJ.Anorectal Crohn’s disease.Surg Clin North Am. 2010 Feb;90(1):83-97, Table of Contents. doi:10.1016/j.suc.2009.09.004MedlinePlus.Hemorrhoids.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Keef KD, Co CA.Control of motility in the internal anal sphincter.J Neurogastroenterol Motil. 2019;25(2):189-204. doi:10.5056/jnm18172Chiarelli M, Guttadauro A, Maternini M, et al.The clinical and therapeutic approach to anal stenosis.Ann Ital Chir.2018;89:237-241.Pisano U, Irvine L, Szczachor J, Jawad A, MacLeod A, Lim M.Anismus, physiology, radiology: Is it time for some pragmatism? A comparative study of radiological and anorectal physiology findings in patients with anismus.Ann Coloproctol. 2016;32(5):170-174. doi:10.3393/ac.2016.32.5.170Johns Hopkins Medicine.Anal fissures.Wood RJ, Levitt MA.Anorectal malformations.Clin Colon Rectal Surg. 2018;31(2):61-70. doi:10.1055/s-0037-1609020Kelley KA, Kaur T, Tsikitis VL.Perianal Crohn’s disease: challenges and solutions.Clin Exp Gastroenterol.2017;10:39-46. doi:10.2147/CEG.S108513Vogel JD, Johnson EK, Morris AM, et al.Clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula.Dis Colon Rectum. 2016;59(12):1117-1133. doi:10.1097/DCR.0000000000000733Johns Hopkins Medicine.Hemorrhoids.Davis BR, Lee-Kong SA, Migaly J, Feingold DL, Steele SR.The American Society of Colon and Rectal Surgeons clinical practice guidelines for the management of hemorrhoids.Dis Colon Rectum. 2018;61(3):284-292. doi:10.1097/DCR.0000000000001030Barros LL, Farias AQ, Rezaie A.Gastrointestinal motility and absorptive disorders in patients with inflammatory bowel diseases: Prevalence, diagnosis and treatment.World J Gastroenterol.2019;25(31):4414-4426. doi:10.3748/wjg.v25.i31.4414North Carolina Surgery UNC Health Care.Anal sphincter repair.Lu Y, Lin A.Lateral Internal Sphincterotomy.JAMA. 2021;325(7):702. doi:10.1001/jama.2020.16708Berg MR, Gregussen H, Sahlin Y.Long-term outcome of sphincteroplasty with separate suturing of the internal and the external anal sphincter.Tech Coloproctol. 2019;23(12):1163-1172. doi:10.1007/s10151-019-02122-7
Keef KD, Co CA.Control of motility in the internal anal sphincter.J Neurogastroenterol Motil. 2019;25(2):189-204. doi:10.5056/jnm18172
Chiarelli M, Guttadauro A, Maternini M, et al.The clinical and therapeutic approach to anal stenosis.Ann Ital Chir.2018;89:237-241.
Pisano U, Irvine L, Szczachor J, Jawad A, MacLeod A, Lim M.Anismus, physiology, radiology: Is it time for some pragmatism? A comparative study of radiological and anorectal physiology findings in patients with anismus.Ann Coloproctol. 2016;32(5):170-174. doi:10.3393/ac.2016.32.5.170
Johns Hopkins Medicine.Anal fissures.
Wood RJ, Levitt MA.Anorectal malformations.Clin Colon Rectal Surg. 2018;31(2):61-70. doi:10.1055/s-0037-1609020
Kelley KA, Kaur T, Tsikitis VL.Perianal Crohn’s disease: challenges and solutions.Clin Exp Gastroenterol.2017;10:39-46. doi:10.2147/CEG.S108513
Vogel JD, Johnson EK, Morris AM, et al.Clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula.Dis Colon Rectum. 2016;59(12):1117-1133. doi:10.1097/DCR.0000000000000733
Johns Hopkins Medicine.Hemorrhoids.
Davis BR, Lee-Kong SA, Migaly J, Feingold DL, Steele SR.The American Society of Colon and Rectal Surgeons clinical practice guidelines for the management of hemorrhoids.Dis Colon Rectum. 2018;61(3):284-292. doi:10.1097/DCR.0000000000001030
Barros LL, Farias AQ, Rezaie A.Gastrointestinal motility and absorptive disorders in patients with inflammatory bowel diseases: Prevalence, diagnosis and treatment.World J Gastroenterol.2019;25(31):4414-4426. doi:10.3748/wjg.v25.i31.4414
North Carolina Surgery UNC Health Care.Anal sphincter repair.
Lu Y, Lin A.Lateral Internal Sphincterotomy.JAMA. 2021;325(7):702. doi:10.1001/jama.2020.16708
Berg MR, Gregussen H, Sahlin Y.Long-term outcome of sphincteroplasty with separate suturing of the internal and the external anal sphincter.Tech Coloproctol. 2019;23(12):1163-1172. doi:10.1007/s10151-019-02122-7
Brisinda G, Vanella S, Cadeddu F, et al.Surgical treatment of anal stenosis.World J Gastroenterol. 2009;15(16):1921-1928. doi:10.3748/wjg.15.1921Lewis RT, Maron DJ.Anorectal Crohn’s disease.Surg Clin North Am. 2010 Feb;90(1):83-97, Table of Contents. doi:10.1016/j.suc.2009.09.004MedlinePlus.Hemorrhoids.
Brisinda G, Vanella S, Cadeddu F, et al.Surgical treatment of anal stenosis.World J Gastroenterol. 2009;15(16):1921-1928. doi:10.3748/wjg.15.1921
Lewis RT, Maron DJ.Anorectal Crohn’s disease.Surg Clin North Am. 2010 Feb;90(1):83-97, Table of Contents. doi:10.1016/j.suc.2009.09.004
MedlinePlus.Hemorrhoids.
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