Rectum: Structure, Function & Sample Questions

Rectum is the largest portion of the large intestine. It is a component of the digestive system. It connects the anus to the gastrointestinal (GI) tract. 

• It is where the body stores excrement before evacuation and is located after the final segment of the colon, known as the sigmoid colon. 
• The end of the large intestine that joins the colon to the anus is known as the rectum. 
• It is where stools are stored before being expelled from the body.

Read More: Digestion and Absorption

Key Terms: Rectum, Digestive tract, Large intestine, Anal canal, Veins, Skin, Tissue, Muscle, Intestine

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Structure of Rectum

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There are two flexures in the rectum.

• Sacral Flexure: Dorsal bend, sometimes referred to as sacral flexion extends from the concave shape of the sacrum.
• Perineal Flexure: The lavatory ani muscle encircles the rectum, causing a perineal flexure, also known as the ventral bend.

The middle rectal fold, known as Kohlrausch's valve, is the strongest one and is situated about 7 cm from the anus.

 

• It is made up of three constant transverse folds termed Houston's valves. 
• The rectal ampulla serves as a reservoir and is extremely extensible throughout the faeces process. 
• The superior rectal artery, middle rectal artery, and inferior rectal artery are the three arteries that make up the rectum.
• The superior, intermediate, and inferior rectal veins, among others, are responsible for carrying out the venous drainage that occurs in the rectum. 
• Superior rectal veins aid the lower part of the rectum drain into the internal iliac vein.
• The middle and inferior rectal veins help the top section of the rectum drain into the portal venous system.
• The mucosa, submucosa, muscularis, and serosa make up the rectum's interior framework.
• The mucosa is made up of the usual intestinal epithelium, which includes many goblet cells and straightforward columnar erythrocytes. 
• However, near the anal transitional zone, this epithelium flattens down to become the stratified squamous epithelium. 
• After the epithelium layer, there is the connective tissue layer, which is composed of lymphatic, muscle, and blood arteries.
• The next layer is the submucosa layer, which is made up of loose connective tissue and contains Meissner's plexus, blood arteries, and lymph follicles. 
• This layer is thickened in the transverse folds and is made up of a network of veins.
• The muscularis layer, which is the final one, is made up of Auerbach's plexus and sits between the inner circular and outer longitudinal musculature. 
• The corrugator cutis ani muscle, which is located in the skin around the anus, is continued by the outside longitudinal musculature and the inner circular or ring musculature in the sphincter system.

Read More: Digestion And Absorption MCQ

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Microscopic Anatomy

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The mucosa, submucosa, muscularis, and serosa/adventitia of the rectum have the same histological characteristics as those of the rest of the large intestine. The acronym "M.S.M.S." makes it simple to recall these layers.

• The mucosa has the usual intestinal epithelium, which includes many goblet cells and straightforward columnar enterocytes. 
• The columnar epithelium gradually flattens at the anal transitional zone and transforms into the stratified squamous non-keratinized epithelium. 
• The connective tissue layer (lamina propria) with blood and lymphatic vessels and a muscle layer follows the epithelium layer (lamina muscularis mucosae).
• The Meissner's plexus, lymph follicles, and blood arteries are all present in the submucosa, which also has loose connective tissue. 
• It is thicker in the transverse folds and possesses an extensive network of veins (rectal venous plexus). 
• The Auerbach's plexus is located between the muscularis' usual inner circular and outer longitudinal musculature. 
• The sphincter system's sphincter ani externus muscle continues the ring musculature. 
• Meanwhile the corrugator cutis ani muscle, which inserts at the skin around the anus, continues the outer longitudinal musculature.

Read More: Digestion and Absorption Revision Notes

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Anal Canal

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The transition of the interior surface of the anal canal, the terminal segment of the digestive tract, from a mucous membrane layer (endodermal) to one of skin-like tissue, distinguishes it from the rectum (ectodermal). 

• The anal canal measures 2.5 to 4 cm (1 to 1.5 inches) in length and has a smaller diameter than the rectum it joins. 
• The canal is divided into three sections: the anal hole itself; the bottom section, which has internal and external constrictive muscles (sphincters) to control faeces evacuation.
• The very top section has longitudinal folds known as rectal columns.

Read More: Absorption

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Clinical Significance of Human Rectum

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Examinations for faecal impaction, prostate malignancy, and faecal incontinence are required in order to make a diagnosis. CT and MRI scans are the medical imaging procedures used to check the rectum. It is possible to insert an ultrasonic probe into the rectum to see the adjacent structures as the prostate. 

• Vasectomy and sigmoidoscopy are endoscopic procedures used to observe the rectum in its natural state. 
• Biopsies are performed in order to diagnose specific disorders, such as cancer.
• A medical thermometer must be placed through the anus into the rectum to measure its temperature. 
• No more than one inch should be added to the thermometer's length. 
• Rectal temperature is typically found to be between 36 and 38 degrees Celsius.

A few clinical diagnoses of rectal issues are described below– 

1. Constipation, one of the major disorders identified, is frequently experienced by persons who lead various lifestyles and consume an unbalanced diet. 

• This includes insufficient hydration or access to water, a diet lacking in fibre, inactivity, and a variety of other factors. 
• These factors may include local diseases, sluggish colon transit time, or illnesses that may damage the nerves that govern bowel movement. 
• Constipation can be brought on by taking drugs like opiates, having a serious sickness, or having diabetes mellitus. 
• High calcium levels or low thyroid function might also contribute to constipation.

2. The linings of the rectum can potentially lead to recurrent rectal cancer. 

• Although the typical causes of rectal cancer are unknown, some doctors believe that there are several risk factors, including age of more than 50, a high-fat diet, smoking, family history, and inflammatory bowel disease.

3. Rectal prolapse can happen after childbirth because of the weaker pelvic floor.

• This is nothing more than the rectum protruding into the external region, or anus.

Read More: Gastric

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Function

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The rectum is the final step located in the anal canal before the evacuation of the faeces. Similar to the colon, the rectum absorbs electrolytes and anaerobic microorganisms break down food that cannot be digested. The rectum measures between 10 and 15 cm, while the colon in a human body is around five feet long overall. Water is absorbed, which causes the stools to thicken and combine with the mucus.

• The rectum is thought to be a component of the continence organ and is primarily responsible for the defecation process. 
• Stretch receptors are found in the rectal ampulla. When faeces enter the ampulla, signals are conveyed to the brain via the central nervous system, which in turn causes the urge to urinate. 
• In order to start or stop the defecation process, the person can now relax or tense the levator ani muscle and the sphincter ani externus. 
• However, the effort required to contain the faeces will grow as well as the abdominal pressure from the diaphragm's and abdominal muscles' voluntary contractions.
• This causes a size reduction of the rectum.

Read More: Indigestion

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Rectal Problems

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1. Rectal Itching: While the itching might cause the skin to grow thick and white, it is not an indication of a serious disorder at first. The skin may initially appear red. There are various causes of itching, including

• After the excrement, the area was not properly cleaned.
• Antibiotics that may result in constipation and diarrhoea.
• Using hot water and potent soap to clean the anus.
• Using perfumed soaps, toilet paper, or ointments.
• Haemorrhoids.
• Bacteria or viruses can cause an infection. The most typical source of itching in youngsters is pinworm.
• Tomatoes, spicy foods, coffee, tea, and foods high in vitamin C4 are a few examples of such foods.
• Some people may experience itching even when travelling for longer lengths of time.

2. Rectal pain: Rectal pain is brought on by a number of factors, including:

• Veins in the lower abdomen that are enlarged or swollen.
• Anal fissures and rectal prolapse are two structural issues.
• Sexually transmitted illnesses cause infection.
• Disease of the rectus.
• Bowel cramps.

3. Rectal Bleeding: Numerous people report experiencing minor rectal bleeding. 

• Due to constipation, haemorrhoids and anal fissures can bleed. 
• This kind of bleeding may result in intestinal discomfort. 
• There may be bleeding anywhere along the digestive tract. 
• The stomach bleeding seems dark and sticky. 
• Near the rectum, blood that exits the digestive tract quickly may appear red. 
• Sometimes the food we eat can affect how coloured the stools are. 
• For example, beets, diarrhoea, and iron supplements can make stools appear red, while blue food colouring can make stools appear black.

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Things to Remember

• Haemorrhoids, in which the veins in the area of the anus and rectum are inflamed, might develop as a result of spending the majority of time in the bathroom.
• Consuming foods high in fibre helps to keep the colon healthy by preventing disorders like diverticulitis and hemorrhoids. 
• Fruits, whole grains, vegetables, nuts, seeds, beans, and legumes are all rich sources of fibre.
• Skin cancer called melanoma, which develops when the skin is not exposed to sunlight, can develop there.
• One should see a doctor if they experience pain in the anal region and blood in the faeces.
• A colonoscopy must be completed by a person who has reached the age of 50 in order to learn about the condition of the colon.