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The rectum is the final straight portion of the large intestine, connecting the colon to the anus. It acts as a temporary storage site for faeces, collecting and holding waste until it is time to release it. The rectum is made up of layers of muscles and tissues, with glands on the inside that secrete and absorb. The rectum has two flexures: the sacral flexure and the perineal flexure, which marks the transition from rectum to anus. The rectum holds waste and absorbs water and electrolytes, solidifying the waste. The rectum's muscles contract and shorten to move waste through, and it stretches to accommodate more waste. The anal sphincter, a group of muscles at the end of the rectum, controls the release of stool.
| Characteristics | Values |
|---|---|
| Location | Between the colon and the anus |
| Length | 10-15 cm (4.7-5.9 inches) |
| Width | 3 inches |
| Shape | Slight "S" shape |
| Structure | Mucosa, submucosa, muscularis, and serosa/adventitia |
| Muscles | Internal and external anal sphincters, corrugator cutis ani, puborectalis, levator ani, and sphincter ani externus |
| Function | Collects and holds solid waste, absorbs water and electrolytes, and facilitates defecation |
| Disorders | Proctitis, rectal ulcers, perianal abscess, hemorrhoids, anal fissures, yeast infections, STIs, abscesses, fistulas, Crohn's disease, incontinence |
| Examinations | Digital rectal exam, anoscopy, barium enema, defecography, blood tests, CT scans, anal manometry, electrophysiological studies, magnetic resonance proctography |
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What You'll Learn
- The rectum is the final straight portion of the large intestine
- The rectum has two flexures: the sacral flexure and the perineal flexure
- The rectum has three or four chambers that help control the movement of contents
- The rectum holds solid waste and absorbs water until it's time to release it
- The rectum has an internal and external anal sphincter to control the release of stool
The rectum is the final straight portion of the large intestine
The rectum is made up of the same layers of muscles and tissues as the colon, with glands on the inside that secrete and absorb. It is between 10 and 15 centimetres long, or about 5 or 6 inches, and can stretch wider than the rest of the intestine to accommodate more waste. It has a slight "S" shape, with two bends: the sacral flexure, which follows the curve of the spine, and the anorectal flexure, which marks the transition from rectum to anus.
The rectum has three or four chambers that help to control the movement of contents through it. The last chamber, the rectal ampulla, is the final reservoir for waste before it is expelled. When this chamber fills, nerve fibres in the rectal wall communicate to the central nervous system that it is time to defecate.
The rectum is supplied by the superior rectal artery and has a microanatomy similar to the rest of the gastrointestinal tract. It possesses a mucosa with a lining of mucus-secreting goblet cells, which rests on a lamina propria, with a layer of smooth muscle called muscularis mucosa. This sits on an underlying submucosa of connective tissue, surrounded by a muscularis propria of two bands of muscle: an inner circular band and an outer longitudinal one.
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The rectum has two flexures: the sacral flexure and the perineal flexure
The rectum is the last part of the large intestine, which connects the sigmoid colon to the anal canal. The anal sphincter, a group of muscles at the end of the rectum, surrounds the anus and controls the release of stool. The rectum has two major flexures: the sacral flexure and the perineal flexure (also known as the anorectal flexure).
The sacral flexure is an anteroposterior curve with concavity anteriorly, which follows the curve of the sacrum and coccyx. The rectum first follows the concavity of the sacrum at the sacral flexure. The sacral flexure results from the concave form of the sacrum.
The perineal flexure is an anteroposterior curve with anterior convexity. This flexure is formed by the tone of the puborectalis muscle and contributes significantly to faecal continence. The perineal flexure is the point of transition to the anal canal (anorectal junction). It is caused by the encirclement of the rectum by the levator ani muscle (puborectal sling).
The rectum is located within the pelvic cavity, between the abdomen and the pelvic floor muscles. It is supported by the pelvic floor muscles, which also aid in the process of defecation and continence. The rectum receives arterial supply through three main arteries: the superior rectal artery, the middle rectal artery, and the inferior rectal artery. The venous drainage of the rectum is carried out by the superior, middle, and inferior rectal veins.
The rectum plays an important role in the defecation process. It acts as a reservoir for stool, collecting and holding it until it is time to release it. The rectum also absorbs water and electrolytes from the stool, further solidifying the waste. When the rectum is full, nerves trigger the urge to have a bowel movement, and the internal anal sphincter relaxes automatically. The external anal sphincter is under conscious control, allowing the individual to hold in the stool until they are ready to defecate.
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The rectum has three or four chambers that help control the movement of contents
The rectum is the last part of the large intestine and is located between the sigmoid colon and the anal canal. The anal sphincter, a group of muscles at the end of the rectum, surrounds the anus and controls the release of stool. The rectum is about 10 to 16 cm long and has a slight "S" shape, with two bends. The rectum has three or four chambers that help control the movement of contents through it. The chambers are separated by permanent transverse folds, also known as Houston's valves, which provide support to the rectal contents.
The last chamber, called the rectal ampulla, is the final reservoir for stool before it exits the body. When this chamber fills, nerve fibres in the rectal wall communicate to the central nervous system that it's time to defecate. The rectal ampulla is quite stretchable, allowing it to serve as a reservoir during defecation. As the pressure in the ampulla increases, it leads to the relaxation of the corrugator cutis ani muscle and the sphincter ani internus muscle, making it more challenging to hold in the stool.
The primary function of the rectum is to collect and hold stool until it's time to release it. It can stretch and expand to accommodate waste as it enters from the colon. While holding the waste, the rectum absorbs remaining water and electrolytes, further solidifying the waste. It also secretes mucus to facilitate smooth passage. The rectum plays a crucial role in the defecation process, including water resorption and electrolyte resorption from the stool.
The rectum is susceptible to various disorders that can affect its inside lining, muscles, or nerves, causing pain and disrupting its normal function. Common conditions include proctitis, rectal ulcers, perianal abscess, and anorectal malformations. These conditions can result in inflammation, pain, bleeding, and other discomforts.
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The rectum holds solid waste and absorbs water until it's time to release it
The rectum is the final straight portion of the large intestine, which lies between the colon and the anus. It is about 4.7 to 6 inches long and acts as a temporary storage site for solid waste, or faeces, before it is released through the anus. The rectum receives faecal material from the descending colon through regular muscle contractions called peristalsis.
The rectum has a higher concentration of goblet cells in its mucosa than other parts of the gastrointestinal tract. The goblet cells secrete mucus, and the rectum also absorbs water and electrolytes (sodium, potassium, chloride) from the stool, further solidifying the waste. The rectum can stretch to accommodate more waste, acting as a reservoir. The three or four chambers of the rectum help to control the movement of contents through it. The last chamber, called the rectal ampulla, is the final reservoir for faeces before it comes out. When this chamber fills, nerve fibres in the rectal wall (stretch receptors) communicate to the central nervous system that it's time to defecate.
The anal sphincter is a group of muscles at the end of the rectum that control the release of stool. There are two muscles: the internal anal sphincter and the external anal sphincter. The internal anal sphincter is located inside the rectum, and the external anal sphincter surrounds the outside end of the anal canal. 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 the stool to be held in until a toilet is reached.
The rectum supports defecation through contraction. The urge to voluntarily defecate occurs when rectal pressure increases beyond 18 mmHg, and reflex expulsion occurs at 55 mmHg. In addition to the contraction of the rectal muscles and relaxation of the external anal sphincter, abdominal muscle contraction and relaxation of the puborectalis muscle are also involved in the process of defecation.
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The rectum has an internal and external anal sphincter to control the release of stool
The rectum is the final straight portion of the large intestine, which is located between the colon and the anus. The rectum is about 4.7 inches long and acts as a temporary storage site for feces. The primary function of the rectum is to collect and hold stool until it is time to release it. The rectum holds the waste and absorbs the remaining water until it is time to release it. The rectum has an internal and external anal sphincter to control the release of stool.
The anal sphincter is a group of muscles at the end of the rectum. The rectum is located at the last few inches of the large intestine (colon). 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. 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.
The internal anal sphincter relaxes automatically when the rectum is full, triggering the urge to have a bowel movement. The external anal sphincter, on the other hand, is under conscious control, allowing individuals to hold in their stool until they are ready to release it. These muscles work together to prevent fecal incontinence and maintain continence.
Damage to the anal sphincter muscles can lead to fecal incontinence, which is the involuntary release of stool from the rectum. This can be distressing and may require surgery to repair the sphincter muscle. Conditions such as Crohn's disease and inflammatory bowel disease can also affect the anal sphincter and lead to incontinence.
The rectum has three or four chambers that help control the movement of contents through it. The last chamber, called the rectal ampulla, is the final reservoir for stool before it comes out. When this chamber fills, nerve fibres communicate to the central nervous system that it is time to defecate. The rectum supports defecation through contraction, and the intra-abdominal pressure is increased through the voluntary tension of the diaphragm and abdominal muscles.
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Frequently asked questions
The rectum is the final straight portion of the large intestine in humans and some other mammals. It is located between the colon and the anus.
The rectum acts as a temporary storage site for feces. It collects and holds poop until it's time to release it.
The rectum has muscles that contract and shorten to move waste through. The rectum supports defecation through these contractions.
The rectum has an inner circular and an outer longitudinal musculature. The outer longitudinal musculature continues as the corrugator cutis ani muscle, which inserts at the skin around the anus. The rectum also has a muscularis mucosa layer.
The anal sphincter is a group of muscles at the end of the rectum that controls the release of stool. It includes the internal anal sphincter and the external anal sphincter. These muscles may be damaged if there is trouble holding in stool, leading to fecal incontinence.
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