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The rectum is the last part of the bowel and is located within the pelvic cavity. It is the most distal segment of the large intestine and has an important role as a temporary store of faeces. The rectum has two flexures: the sacral flexure (dorsal bend) and the perineal flexure (ventral bend). The rectum is surrounded by several muscles, including the internal and external anal sphincters, which control the release of stool. The puborectalis muscle wraps around the lower rectum and relaxes to allow the rectum to straighten and pass stool. The rectum also has a muscle layer (lamina muscularis mucosae) and the typical inner circular and outer longitudinal musculature.
| Characteristics | Values |
|---|---|
| Location | The rectum is the last part of the bowel, located at the last few inches of the large intestine (colon) |
| Function | The rectum temporarily stores faeces, stretching to accommodate stool from the colon. It is also part of the continence organ, playing a role in defecation. |
| Muscles | The anal sphincter is a group of muscles at the end of the rectum, consisting of the internal anal sphincter and the external anal sphincter. The puborectalis muscle wraps around the lower rectum and helps to keep stool in. |
| Blood Supply | The rectum receives arterial supply through three main arteries: the superior rectal artery, the middle rectal artery, and the inferior rectal artery. |
| Innervation | The rectum receives sympathetic supply from the lumbar splanchnic nerves and superior and inferior hypogastric plexuses. Parasympathetic supply is from S2-4 via the pelvic splanchnic nerves and inferior hypogastric plexuses. |
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What You'll Learn
- The anal sphincter is a group of muscles at the end of the rectum
- The rectum is formed of the usual layers of the large intestine, including a muscle layer
- The puborectalis muscle wraps around the lower rectum, creating an angle to keep stool in
- The rectum is surrounded by the levator ani muscle, which forms the perineal flexure
- The internal and external anal sphincter muscles work together to control the release of stool
The anal sphincter is a group of muscles at the end of the rectum
The anal sphincter is made up of two muscles: the internal anal sphincter and the external anal sphincter. The internal anal sphincter is located inside the rectum, while the external anal sphincter goes around the outside of the end of the anal canal. These muscles work together to control the release of stool. When the rectum is full, the internal anal sphincter relaxes automatically, and the external sphincter can be squeezed to hold stool in until a person is ready to release it.
The rectum has an important role in storing faeces temporarily. It is continuous proximally with the sigmoid colon and terminates into the anal canal. The rectum receives arterial supply through three main arteries: the superior rectal artery, the middle rectal artery, and the inferior rectal artery. It also receives sensory and autonomic innervation.
The rectum has two flexures: the sacral flexure (dorsal bend) and the perineal flexure (ventral bend). The transition to the anal canal occurs at the perineal flexure. The rectum is similar in structure to the rest of the large intestine, with mucosa, submucosa, muscularis, and serosa/adventitia layers. The muscularis layer includes inner circular and outer longitudinal musculature, with the sphincter ani externus muscle being part of the sphincter system.
The anal sphincter muscles may be damaged if a person has trouble holding in stool or urine, or if they experience pain in the rectum. Conditions such as Crohn's disease can also affect the anal sphincter, and surgery may be required to repair or remove the sphincter in some cases.
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The rectum is formed of the usual layers of the large intestine, including a muscle layer
The rectum is the last part of the bowel and is located within the pelvic cavity. It is the most distal segment of the large intestine, where faeces are temporarily stored. The rectum is morphologically similar to the rest of the large intestine, with the usual layers of mucosa, submucosa, muscularis, and serosa/adventitia.
The rectum has a muscle layer, the muscularis, which has an inner circular and outer longitudinal musculature. The Auerbach's plexus lies between these two layers. The outer longitudinal musculature continues as the corrugator cutis ani muscle, which inserts at the skin around the anus. The inner circular musculature continues as the sphincter ani externus muscle, which is part of the anal sphincter.
The anal sphincter is a group of muscles at the end of the rectum that controls the release of stool. It consists of two muscles: the internal anal sphincter and the external anal sphincter. The internal anal sphincter is located inside the rectum, while the external anal sphincter surrounds the outside end of the anal canal. These muscles work together to maintain continence and control the release of stool.
In addition to the anal sphincter muscles, other muscles also play a role in the process of defecation. The puborectalis muscle wraps around the lower rectum and creates an angle in the rectum to keep stool in. During a bowel movement, the puborectalis muscle relaxes and contracts, straightening the rectum and allowing stool to pass. Muscles in the abdominal wall contract, increasing pressure in the rectum and helping to push stool down.
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The puborectalis muscle wraps around the lower rectum, creating an angle to keep stool in
The rectum is located at the last few inches of the large intestine. The anal sphincter, a group of muscles at the end of the rectum, surrounds the anus and controls the release of stool. The anal sphincter comprises two muscles: the internal anal sphincter and the external anal sphincter.
The puborectalis muscle is a loop of muscle that wraps around the lower rectum. It forms the pelvic floor and surrounds the rectum posteriorly and laterally to create an angle between the anus and rectum to help preserve continence. The contraction of the puborectalis muscle pushes the rectum forward and upward, making the angle between the rectum and anal canal more acute and preventing the passage of its contents. This process works less well when stool contents are watery since the stool can more easily slip around this angle.
During defaecation, the puborectalis muscle relaxes, reducing the sling effect and, therefore, the anorectal angle. The rectum straightens as a result, facilitating rectal emptying as the anal sphincters relax. This whole process is entirely dependent on the nervous innervation of the rectum and anus. During normal rectal emptying, the following changes are observed:
- As straining begins, abdominal pressure produces a slight concavity of the anterior rectal wall.
- The pelvic floor descends.
- The anorectal angle widens.
- The anal canal begins to open, shortens and becomes funnel-shaped.
In dyssynergic types of constipation, there is a paradoxical contraction of pelvic floor muscles (i.e. puborectalis muscle and external anal sphincter) leading to a significantly impaired ability to expel stool during attempts to defecate.
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The rectum is surrounded by the levator ani muscle, which forms the perineal flexure
The rectum is the last part of the bowel, receiving stool from the colon. It is located within the pelvic cavity and is the most posterior of the pelvic viscera. The rectum is the most distal segment of the large intestine and acts as a temporary store of faeces. It is continuous proximally with the sigmoid colon and terminates into the anal canal. The anal canal is the last two inches of the large intestine.
The rectum has two flexures: the sacral flexure, which is a dorsal bend resulting from the concave form of the sacrum, and the perineal flexure, which is a ventral bend caused by the encirclement of the rectum by the levator ani muscle. The perineal flexure is the point of transition to the anal canal. The rectum is supplied by three main arteries: the superior rectal artery, the middle rectal artery, and the inferior rectal artery. It receives sympathetic nervous supply from the lumbar splanchnic nerves and superior and inferior hypogastric plexuses.
The rectum plays an important role in the mechanism of defecation. When the rectum is full, nerves trigger the urge to have a bowel movement, and the internal anal sphincter relaxes automatically. The external sphincter is under conscious control, allowing an individual to hold in stool until they are ready to release it. During a bowel movement, the rectum contracts, and stool is pushed through the anus and out of the body.
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The internal and external anal sphincter muscles work together to control the release of stool
The rectum is the last part of the bowel, located at the end of the large intestine. It is a temporary storage site for faeces and is responsible for absorbing electrolytes and water from stool. The rectum is also involved in the decomposition of indigestible food by anaerobic bacteria.
The anal sphincter is a group of muscles at the end of the rectum that controls the release of stool. It consists of two muscles: the internal anal sphincter and the external anal sphincter. These muscles work together to maintain continence and control the release of stool. The internal anal sphincter is located inside the rectum, while the external anal sphincter surrounds the outside of the end of the anal canal.
When the rectum is full, nerves trigger the urge to have a bowel movement. The internal anal sphincter relaxes automatically, and the external sphincter can be consciously contracted to hold stool in. The puborectalis muscle, a loop of muscle that wraps around the lower rectum, also helps to keep stool in by creating an angle in the rectum and contracting when the external sphincter is squeezed.
During a bowel movement, the rectum contracts and several muscles work together in a coordinated way to push stool out through the anus. Muscles in the abdominal wall contract, increasing pressure in the rectum and aiding in the expulsion of stool. The internal and external anal sphincters relax, along with the pelvic floor muscles, to allow stool to pass out of the body.
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Frequently asked questions
The rectum is the last part of the bowel, located at the end of the large intestine. It is a temporary store of faeces before they are eliminated through the anal canal.
The rectum is formed by the typical inner circular and outer longitudinal musculature. The internal anal sphincter and the external anal sphincter are part of the rectum. The puborectalis muscle is also a loop of muscle that wraps around the lower rectum.
The rectal muscles, along with the pelvic floor muscles, control the release of stool. The internal anal sphincter contracts to keep stool in and relaxes when the rectum is full. The external anal sphincter can be squeezed to hold stool in.
Fecal incontinence, or the involuntary release of stool, can occur due to damage to the anal sphincter muscles or flare-ups of IBD. Anal fissures, tears in the lining of the anus, can also extend into the internal anal sphincter and cause pain during bowel movements.
